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[gnutls.git] / doc / protocol / draft-ietf-tls-rfc2246-bis-06.txt

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                                                              Tim Dierks |\r
                                                                  Google |\r
                                                           Eric Rescorla |\r
INTERNET-DRAFT                                                RTFM, Inc. |\r
<draft-ietf-tls-rfc2246-bis-06.txt>  March 2004 (Expires September 2004) |\r
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                            The TLS Protocol\r
                              Version 1.1                                |\r
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Status of this Memo\r
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   This document is an Internet-Draft and is in full conformance with    |\r
   all provisions of Section 10 of RFC2026.  Internet-Drafts are working |\r
   documents of the Internet Engineering Task Force (IETF), its areas,   |\r
   and its working groups.  Note that other groups may also distribute   |\r
   working documents as Internet-Drafts.                                 |\r
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   Internet-Drafts are draft documents valid for a maximum of six months |\r
   and may be updated, replaced, or obsoleted by other documents at any  |\r
   time.  It is inappropriate to use Internet-Drafts as reference        |\r
   material or to cite them other than as "work in progress."            |\r
\r
\r
   To learn the current status of any Internet-Draft, please check the   |\r
   "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow   |\r
   Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),         |\r
   munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or         |\r
   ftp.isi.edu (US West Coast).\r
Copyright Notice\r
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   Copyright (C) The Internet Society (1999-2004).  All Rights Reserved. |\r
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Abstract\r
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   This document specifies Version 1.1 of the Transport Layer Security   |\r
   (TLS) protocol. The TLS protocol provides communications security\r
   over the Internet. The protocol allows client/server applications to\r
   communicate in a way that is designed to prevent eavesdropping,\r
   tampering, or message forgery.\r
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Table of Contents\r
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   1.       Introduction                                              3\r
   2.       Goals                                                     4\r
   3.       Goals of this document                                    5\r
   4.       Presentation language                                     5\r
   4.1.     Basic block size                                          6\r
   4.2.     Miscellaneous                                             6\r
   4.3.     Vectors                                                   6\r
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Dierks & Rescorla            Standards Track                     [Page 1] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
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   4.4.     Numbers                                                   7\r
   4.5.     Enumerateds                                               7\r
   4.6.     Constructed types                                         8\r
   4.6.1.   Variants                                                  9\r
   4.7.     Cryptographic attributes                                 10\r
   4.8.     Constants                                                11\r
   5.       HMAC and the pseudorandom function                       11\r
   6.       The TLS Record Protocol                                  13\r
   6.1.     Connection states                                        14\r
   6.2.     Record layer                                             16\r
   6.2.1.   Fragmentation                                            16\r
   6.2.2.   Record compression and decompression                     17\r
   6.2.3.   Record payload protection                                18\r
   6.2.3.1. Null or standard stream cipher                           19\r
   6.2.3.2. CBC block cipher                                         19\r
   6.3.     Key calculation                                          21\r
   6.3.1.   Export key generation example                            22\r
   7.       The TLS Handshake Protocol                               23\r
   7.1.     Change cipher spec protocol                              24\r
   7.2.     Alert protocol                                           24\r
   7.2.1.   Closure alerts                                           25\r
   7.2.2.   Error alerts                                             26\r
   7.3.     Handshake Protocol overview                              29\r
   7.4.     Handshake protocol                                       32\r
   7.4.1.   Hello messages                                           33\r
   7.4.1.1. Hello request                                            33\r
   7.4.1.2. Client hello                                             34\r
   7.4.1.3. Server hello                                             36\r
   7.4.2.   Server certificate                                       37\r
   7.4.3.   Server key exchange message                              39\r
   7.4.4.   Certificate request                                      41\r
   7.4.5.   Server hello done                                        42\r
   7.4.6.   Client certificate                                       43\r
   7.4.7.   Client key exchange message                              43\r
   7.4.7.1. RSA encrypted premaster secret message                   44\r
   7.4.7.2. Client Diffie-Hellman public value                       45\r
   7.4.8.   Certificate verify                                       45\r
   7.4.9.   Finished                                                 46\r
   8.       Cryptographic computations                               47\r
   8.1.     Computing the master secret                              47\r
   8.1.1.   RSA                                                      48\r
   8.1.2.   Diffie-Hellman                                           48\r
   9.       Mandatory Cipher Suites                                  48\r
   10.      Application data protocol                                48\r
   A.       Protocol constant values                                 49\r
   A.1.     Record layer                                             49\r
   A.2.     Change cipher specs message                              50\r
   A.3.     Alert messages                                           50\r
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   A.4.     Handshake protocol                                       51\r
   A.4.1.   Hello messages                                           51\r
   A.4.2.   Server authentication and key exchange messages          52\r
   A.4.3.   Client authentication and key exchange messages          53\r
   A.4.4.   Handshake finalization message                           54\r
   A.5.     The CipherSuite                                          54\r
   A.6.     The Security Parameters                                  56\r
   B.       Glossary                                                 57\r
   C.       CipherSuite definitions                                  61\r
   D.       Implementation Notes                                     64\r
   D.1.     Temporary RSA keys                                       64\r
   D.2.     Random Number Generation and Seeding                     64\r
   D.3.     Certificates and authentication                          65\r
   D.4.     CipherSuites                                             65\r
   E.       Backward Compatibility With SSL                          66\r
   E.1.     Version 2 client hello                                   67\r
   E.2.     Avoiding man-in-the-middle version rollback              68\r
   F.       Security analysis                                        69\r
   F.1.     Handshake protocol                                       69\r
   F.1.1.   Authentication and key exchange                          69\r
   F.1.1.1. Anonymous key exchange                                   69\r
   F.1.1.2. RSA key exchange and authentication                      70\r
   F.1.1.3. Diffie-Hellman key exchange with authentication          71\r
   F.1.2.   Version rollback attacks                                 71\r
   F.1.3.   Detecting attacks against the handshake protocol         72\r
   F.1.4.   Resuming sessions                                        72\r
   F.1.5.   MD5 and SHA                                              72\r
   F.2.     Protecting application data                              72\r
   F.3.     Final notes                                              73\r
   G.       Patent Statement                                         74\r
            Security Considerations                                  75\r
            References                                               75\r
            Credits                                                  77\r
            Comments                                                 78\r
            Full Copyright Statement                   80\r
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Change history                                                           |\r
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   Note: Change bars in this draft are from RFC 2246, not draft-00       |\r
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   26-Jun-03 ekr@rtfm.com                                                |\r
    * Incorporated Last Call comments from Franke Marcus, Jack Lloyd,    |\r
    Brad Wetmore, and others.                                            |\r
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   22-Apr-03 ekr@rtfm.com                                                |\r
    * coverage of the Vaudenay, Boneh-Brumley, and KPR attacks           |\r
    * cleaned up IV text a bit.                                          |\r
    * Added discussion of Denial of Service attacks.                     |\r
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Dierks & Rescorla            Standards Track                     [Page 3] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
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                                                                         |\r
   11-Feb-02 ekr@rtfm.com                                                |\r
    * Clarified the behavior of empty certificate lists [Nelson Bolyard] |\r
    * Added text explaining the security implications of authenticate    |\r
      then encrypt.                                                      |\r
    * Cleaned up the explicit IV text.                                   |\r
    * Added some more acknowledgement names                              |\r
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   02-Nov-02 ekr@rtfm.com                                                |\r
    * Changed this to be TLS 1.1.                                        |\r
    * Added fixes for the Rogaway and Vaudenay CBC attacks               |\r
    * Separated references into normative and informative                |\r
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   01-Mar-02 ekr@rtfm.com                                                |\r
    * Tightened up the language in F.1.1.2 [Peter Watkins]               |\r
    * Fixed smart quotes [Bodo Moeller]                                  |\r
    * Changed handling of padding errors to prevent CBC-based attack     |\r
      [Bodo Moeller]                                                     |\r
    * Fixed certificate_list spec in the appendix [Aman Sawrup]          |\r
    * Fixed a bug in the V2 definitions [Aman Sawrup]                    |\r
    * Fixed S 7.2.1 to point out that you don't need a close notify      |\r
      if you just sent some other fatal alert [Andreas Sterbenz]         |\r
    * Marked alert 41 reserved [Andreas Sterbenz]                        |\r
    * Changed S 7.4.2 to point out that 512-bit keys cannot be used for  |\r
      signing [Andreas Sterbenz]                                         |\r
    * Added reserved client key types from SSLv3 [Andreas Sterbenz]      |\r
    * Changed EXPORT40 to "40-bit EXPORT" in S 9 [Andreas Sterbenz]      |\r
    * Removed RSA patent statement [Andreas Sterbenz]                    |\r
    * Removed references to BSAFE and RSAREF [Andreas Sterbenz]          |\r
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   14-Feb-02 ekr@rtfm.com                                                |\r
    * Re-converted to I-D from RFC                                       |\r
    * Made RSA/3DES the mandatory cipher suite.                          |\r
    * Added discussion of the EncryptedPMS encoding and PMS version number|\r
      issues to 7.4.7.1                                                  |\r
    * Removed the requirement in 7.4.1.3 that the Server random must be  |\r
      different from the Client random, since these are randomly generated|\r
      and we don't expect servers to reject Server random values which   |\r
      coincidentally are the same as the Client random.                  |\r
    * Replaced may/should/must with MAY/SHOULD/MUST where appropriate.   |\r
      In many cases, shoulds became MUSTs, where I believed that was the |\r
      actual sense of the text. Added an RFC 2119 bulletin.              |\r
   * Clarified the meaning of "empty certificate" message. [Peter Gutmann]|\r
   * Redid the CertificateRequest grammar to allow no distinguished names.|\r
     [Peter Gutmann]                                                     |\r
   * Removed the reference to requiring the master secret to generate    |\r
     the CertificateVerify in F.1.1 [Bodo Moeller]                       |\r
   * Deprecated EXPORT40.                                                |\r
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   * Fixed a bunch of errors in the SSLv2 backward compatible client hello.|\r
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1. Introduction\r
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   The primary goal of the TLS Protocol is to provide privacy and data\r
   integrity between two communicating applications. The protocol is\r
   composed of two layers: the TLS Record Protocol and the TLS Handshake\r
   Protocol. At the lowest level, layered on top of some reliable\r
   transport protocol (e.g., TCP[TCP]), is the TLS Record Protocol. The\r
   TLS Record Protocol provides connection security that has two basic\r
   properties:\r
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     - - The connection is private. Symmetric cryptography is used for\r
       data encryption (e.g., DES [DES], RC4 [RC4], etc.) The keys for\r
       this symmetric encryption are generated uniquely for each\r
       connection and are based on a secret negotiated by another\r
       protocol (such as the TLS Handshake Protocol). The Record\r
       Protocol can also be used without encryption.\r
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     - - The connection is reliable. Message transport includes a\r
       message integrity check using a keyed MAC. Secure hash functions\r
       (e.g., SHA, MD5, etc.) are used for MAC computations. The Record\r
       Protocol can operate without a MAC, but is generally only used in\r
       this mode while another protocol is using the Record Protocol as\r
       a transport for negotiating security parameters.\r
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   The TLS Record Protocol is used for encapsulation of various higher\r
   level protocols. One such encapsulated protocol, the TLS Handshake\r
   Protocol, allows the server and client to authenticate each other and\r
   to negotiate an encryption algorithm and cryptographic keys before\r
   the application protocol transmits or receives its first byte of\r
   data. The TLS Handshake Protocol provides connection security that\r
   has three basic properties:\r
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     - - The peer's identity can be authenticated using asymmetric, or\r
       public key, cryptography (e.g., RSA [RSA], DSS [DSS], etc.). This\r
       authentication can be made optional, but is generally required\r
       for at least one of the peers.\r
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     - - The negotiation of a shared secret is secure: the negotiated    |\r
       secret is unavailable to eavesdroppers, and for any authenticated\r
       connection the secret cannot be obtained, even by an attacker who\r
       can place himself in the middle of the connection.\r
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     - - The negotiation is reliable: no attacker can modify the\r
       negotiation communication without being detected by the parties\r
       to the communication.\r
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   One advantage of TLS is that it is application protocol independent.\r
   Higher level protocols can layer on top of the TLS Protocol\r
   transparently. The TLS standard, however, does not specify how\r
   protocols add security with TLS; the decisions on how to initiate TLS\r
   handshaking and how to interpret the authentication certificates\r
   exchanged are left up to the judgment of the designers and\r
   implementors of protocols which run on top of TLS.\r
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1.1 Requirements Terminology                                             |\r
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   Keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT" and   |\r
   "MAY" that appear in this document are to be interpreted as described |\r
   in RFC 2119 [REQ].                                                    |\r
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2. Goals\r
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   The goals of TLS Protocol, in order of their priority, are:\r
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    1. Cryptographic security: TLS should be used to establish a secure\r
       connection between two parties.\r
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    2. Interoperability: Independent programmers should be able to\r
       develop applications utilizing TLS that will then be able to\r
       successfully exchange cryptographic parameters without knowledge\r
       of one another's code.\r
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    3. Extensibility: TLS seeks to provide a framework into which new\r
       public key and bulk encryption methods can be incorporated as\r
       necessary. This will also accomplish two sub-goals: to prevent\r
       the need to create a new protocol (and risking the introduction\r
       of possible new weaknesses) and to avoid the need to implement an\r
       entire new security library.\r
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    4. Relative efficiency: Cryptographic operations tend to be highly\r
       CPU intensive, particularly public key operations. For this\r
       reason, the TLS protocol has incorporated an optional session\r
       caching scheme to reduce the number of connections that need to\r
       be established from scratch. Additionally, care has been taken to\r
       reduce network activity.\r
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3. Goals of this document\r
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   This document and the TLS protocol itself are based on the SSL 3.0\r
   Protocol Specification as published by Netscape. The differences\r
   between this protocol and SSL 3.0 are not dramatic, but they are\r
   significant enough that TLS 1.0 and SSL 3.0 do not interoperate\r
   (although TLS 1.0 does incorporate a mechanism by which a TLS\r
   implementation can back down to SSL 3.0). This document is intended\r
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   primarily for readers who will be implementing the protocol and those\r
   doing cryptographic analysis of it. The specification has been\r
   written with this in mind, and it is intended to reflect the needs of\r
   those two groups. For that reason, many of the algorithm-dependent\r
   data structures and rules are included in the body of the text (as\r
   opposed to in an appendix), providing easier access to them.\r
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   This document is not intended to supply any details of service\r
   definition nor interface definition, although it does cover select\r
   areas of policy as they are required for the maintenance of solid\r
   security.\r
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4. Presentation language\r
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   This document deals with the formatting of data in an external\r
   representation. The following very basic and somewhat casually\r
   defined presentation syntax will be used. The syntax draws from\r
   several sources in its structure. Although it resembles the\r
   programming language "C" in its syntax and XDR [XDR] in both its\r
   syntax and intent, it would be risky to draw too many parallels. The\r
   purpose of this presentation language is to document TLS only, not to\r
   have general application beyond that particular goal.\r
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4.1. Basic block size\r
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   The representation of all data items is explicitly specified. The\r
   basic data block size is one byte (i.e. 8 bits). Multiple byte data\r
   items are concatenations of bytes, from left to right, from top to\r
   bottom. From the bytestream a multi-byte item (a numeric in the\r
   example) is formed (using C notation) by:\r
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       value = (byte[0] << 8*(n-1)) | (byte[1] << 8*(n-2)) |\r
               ... | byte[n-1];\r
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   This byte ordering for multi-byte values is the commonplace network\r
   byte order or big endian format.\r
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4.2. Miscellaneous\r
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   Comments begin with "/*" and end with "*/".\r
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   Optional components are denoted by enclosing them in "[[ ]]" double\r
   brackets.\r
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   Single byte entities containing uninterpreted data are of type\r
   opaque.\r
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4.3. Vectors\r
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   A vector (single dimensioned array) is a stream of homogeneous data\r
   elements. The size of the vector may be specified at documentation\r
   time or left unspecified until runtime. In either case the length\r
   declares the number of bytes, not the number of elements, in the\r
   vector. The syntax for specifying a new type T' that is a fixed\r
   length vector of type T is\r
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       T T'[n];\r
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   Here T' occupies n bytes in the data stream, where n is a multiple of\r
   the size of T. The length of the vector is not included in the\r
   encoded stream.\r
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   In the following example, Datum is defined to be three consecutive\r
   bytes that the protocol does not interpret, while Data is three\r
   consecutive Datum, consuming a total of nine bytes.\r
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       opaque Datum[3];      /* three uninterpreted bytes */\r
       Datum Data[9];        /* 3 consecutive 3 byte vectors */\r
\r
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   Variable length vectors are defined by specifying a subrange of legal\r
   lengths, inclusively, using the notation <floor..ceiling>.  When\r
   encoded, the actual length precedes the vector's contents in the byte\r
   stream. The length will be in the form of a number consuming as many\r
   bytes as required to hold the vector's specified maximum (ceiling)\r
   length. A variable length vector with an actual length field of zero\r
   is referred to as an empty vector.\r
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       T T'<floor..ceiling>;\r
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   In the following example, mandatory is a vector that must contain\r
   between 300 and 400 bytes of type opaque. It can never be empty. The\r
   actual length field consumes two bytes, a uint16, sufficient to\r
   represent the value 400 (see Section 4.4). On the other hand, longer\r
   can represent up to 800 bytes of data, or 400 uint16 elements, and it\r
   may be empty. Its encoding will include a two byte actual length\r
   field prepended to the vector. The length of an encoded vector must\r
   be an even multiple of the length of a single element (for example, a\r
   17 byte vector of uint16 would be illegal).\r
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       opaque mandatory<300..400>;\r
             /* length field is 2 bytes, cannot be empty */\r
       uint16 longer<0..800>;\r
             /* zero to 400 16-bit unsigned integers */\r
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4.4. Numbers\r
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   The basic numeric data type is an unsigned byte (uint8). All larger\r
   numeric data types are formed from fixed length series of bytes\r
   concatenated as described in Section 4.1 and are also unsigned. The\r
   following numeric types are predefined.\r
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       uint8 uint16[2];\r
       uint8 uint24[3];\r
       uint8 uint32[4];\r
       uint8 uint64[8];\r
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   All values, here and elsewhere in the specification, are stored in\r
   "network" or "big-endian" order; the uint32 represented by the hex\r
   bytes 01 02 03 04 is equivalent to the decimal value 16909060.\r
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4.5. Enumerateds\r
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   An additional sparse data type is available called enum. A field of\r
   type enum can only assume the values declared in the definition.\r
   Each definition is a different type. Only enumerateds of the same\r
   type may be assigned or compared. Every element of an enumerated must\r
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   be assigned a value, as demonstrated in the following example.  Since\r
   the elements of the enumerated are not ordered, they can be assigned\r
   any unique value, in any order.\r
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       enum { e1(v1), e2(v2), ... , en(vn) [[, (n)]] } Te;\r
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   Enumerateds occupy as much space in the byte stream as would its\r
   maximal defined ordinal value. The following definition would cause\r
   one byte to be used to carry fields of type Color.\r
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       enum { red(3), blue(5), white(7) } Color;\r
\r
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   One may optionally specify a value without its associated tag to\r
   force the width definition without defining a superfluous element.\r
   In the following example, Taste will consume two bytes in the data\r
   stream but can only assume the values 1, 2 or 4.\r
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       enum { sweet(1), sour(2), bitter(4), (32000) } Taste;\r
\r
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   The names of the elements of an enumeration are scoped within the\r
   defined type. In the first example, a fully qualified reference to\r
   the second element of the enumeration would be Color.blue. Such\r
   qualification is not required if the target of the assignment is well\r
   specified.\r
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       Color color = Color.blue;     /* overspecified, legal */\r
       Color color = blue;           /* correct, type implicit */\r
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   For enumerateds that are never converted to external representation,\r
   the numerical information may be omitted.\r
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       enum { low, medium, high } Amount;\r
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4.6. Constructed types\r
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   Structure types may be constructed from primitive types for\r
   convenience. Each specification declares a new, unique type. The\r
   syntax for definition is much like that of C.\r
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       struct {\r
         T1 f1;\r
         T2 f2;\r
         ...\r
         Tn fn;\r
       } [[T]];\r
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   The fields within a structure may be qualified using the type's name\r
   using a syntax much like that available for enumerateds. For example,\r
   T.f2 refers to the second field of the previous declaration.\r
   Structure definitions may be embedded.\r
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4.6.1. Variants\r
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   Defined structures may have variants based on some knowledge that is\r
   available within the environment. The selector must be an enumerated\r
   type that defines the possible variants the structure defines. There\r
   must be a case arm for every element of the enumeration declared in\r
   the select. The body of the variant structure may be given a label\r
   for reference. The mechanism by which the variant is selected at\r
   runtime is not prescribed by the presentation language.\r
\r
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       struct {\r
           T1 f1;\r
           T2 f2;\r
           ....\r
           Tn fn;\r
           select (E) {\r
               case e1: Te1;\r
               case e2: Te2;\r
               ....\r
               case en: Ten;\r
           } [[fv]];\r
       } [[Tv]];\r
\r
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   For example:\r
\r
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       enum { apple, orange } VariantTag;\r
       struct {\r
           uint16 number;\r
           opaque string<0..10>; /* variable length */\r
       } V1;\r
       struct {\r
           uint32 number;\r
           opaque string[10];    /* fixed length */\r
       } V2;\r
       struct {\r
           select (VariantTag) { /* value of selector is implicit */\r
               case apple: V1;   /* VariantBody, tag = apple */\r
               case orange: V2;  /* VariantBody, tag = orange */\r
           } variant_body;       /* optional label on variant */\r
       } VariantRecord;\r
\r
\r
   Variant structures may be qualified (narrowed) by specifying a value\r
   for the selector prior to the type. For example, a\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 11] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
       orange VariantRecord\r
\r
\r
   is a narrowed type of a VariantRecord containing a variant_body of\r
   type V2.\r
\r
\r
4.7. Cryptographic attributes\r
\r
\r
   The four cryptographic operations digital signing, stream cipher\r
   encryption, block cipher encryption, and public key encryption are\r
   designated digitally-signed, stream-ciphered, block-ciphered, and\r
   public-key-encrypted, respectively. A field's cryptographic\r
   processing is specified by prepending an appropriate key word\r
   designation before the field's type specification. Cryptographic keys\r
   are implied by the current session state (see Section 6.1).\r
\r
\r
   In digital signing, one-way hash functions are used as input for a\r
   signing algorithm. A digitally-signed element is encoded as an opaque\r
   vector <0..2^16-1>, where the length is specified by the signing\r
   algorithm and key.\r
\r
\r
   In RSA signing, a 36-byte structure of two hashes (one SHA and one\r
   MD5) is signed (encrypted with the private key). It is encoded with\r
   PKCS #1 block type 0 or type 1 as described in [PKCS1].\r
\r
\r
   In DSS, the 20 bytes of the SHA hash are run directly through the\r
   Digital Signing Algorithm with no additional hashing. This produces\r
   two values, r and s. The DSS signature is an opaque vector, as above,\r
   the contents of which are the DER encoding of:\r
\r
\r
       Dss-Sig-Value  ::=  SEQUENCE  {\r
            r       INTEGER,\r
            s       INTEGER\r
       }\r
\r
\r
   In stream cipher encryption, the plaintext is exclusive-ORed with an\r
   identical amount of output generated from a cryptographically-secure\r
   keyed pseudorandom number generator.\r
\r
\r
   In block cipher encryption, every block of plaintext encrypts to a\r
   block of ciphertext. All block cipher encryption is done in CBC\r
   (Cipher Block Chaining) mode, and all items which are block-ciphered\r
   will be an exact multiple of the cipher block length.\r
\r
\r
   In public key encryption, a public key algorithm is used to encrypt\r
   data in such a way that it can be decrypted only with the matching\r
   private key. A public-key-encrypted element is encoded as an opaque\r
   vector <0..2^16-1>, where the length is specified by the signing\r
   algorithm and key.\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 12] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   An RSA encrypted value is encoded with PKCS #1 block type 2 as\r
   described in [PKCS1].\r
\r
\r
   In the following example:\r
\r
\r
       stream-ciphered struct {\r
           uint8 field1;\r
           uint8 field2;\r
           digitally-signed opaque hash[20];\r
       } UserType;\r
\r
\r
   The contents of hash are used as input for the signing algorithm,\r
   then the entire structure is encrypted with a stream cipher. The\r
   length of this structure, in bytes would be equal to 2 bytes for\r
   field1 and field2, plus two bytes for the length of the signature,\r
   plus the length of the output of the signing algorithm. This is known\r
   due to the fact that the algorithm and key used for the signing are\r
   known prior to encoding or decoding this structure.\r
\r
\r
4.8. Constants\r
\r
\r
   Typed constants can be defined for purposes of specification by\r
   declaring a symbol of the desired type and assigning values to it.\r
   Under-specified types (opaque, variable length vectors, and\r
   structures that contain opaque) cannot be assigned values. No fields\r
   of a multi-element structure or vector may be elided.\r
\r
\r
   For example,\r
\r
\r
       struct {\r
           uint8 f1;\r
           uint8 f2;\r
       } Example1;\r
\r
\r
       Example1 ex1 = {1, 4};  /* assigns f1 = 1, f2 = 4 */\r
\r
\r
5. HMAC and the pseudorandom function\r
\r
\r
   A number of operations in the TLS record and handshake layer required\r
   a keyed MAC; this is a secure digest of some data protected by a\r
   secret. Forging the MAC is infeasible without knowledge of the MAC\r
   secret. The construction we use for this operation is known as HMAC,\r
   described in [HMAC].\r
\r
\r
   HMAC can be used with a variety of different hash algorithms. TLS\r
   uses it in the handshake with two different algorithms: MD5 and\r
   SHA-1, denoting these as HMAC_MD5(secret, data) and HMAC_SHA(secret,\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 13] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   data). Additional hash algorithms can be defined by cipher suites and\r
   used to protect record data, but MD5 and SHA-1 are hard coded into\r
   the description of the handshaking for this version of the protocol.\r
\r
\r
   In addition, a construction is required to do expansion of secrets\r
   into blocks of data for the purposes of key generation or validation.\r
   This pseudo-random function (PRF) takes as input a secret, a seed,\r
   and an identifying label and produces an output of arbitrary length.\r
\r
\r
   In order to make the PRF as secure as possible, it uses two hash\r
   algorithms in a way which should guarantee its security if either\r
   algorithm remains secure.\r
\r
\r
   First, we define a data expansion function, P_hash(secret, data)\r
   which uses a single hash function to expand a secret and seed into an\r
   arbitrary quantity of output:\r
\r
\r
       P_hash(secret, seed) = HMAC_hash(secret, A(1) + seed) +\r
                              HMAC_hash(secret, A(2) + seed) +\r
                              HMAC_hash(secret, A(3) + seed) + ...\r
\r
\r
   Where + indicates concatenation.\r
\r
\r
   A() is defined as:\r
       A(0) = seed\r
       A(i) = HMAC_hash(secret, A(i-1))\r
\r
\r
   P_hash can be iterated as many times as is necessary to produce the\r
   required quantity of data. For example, if P_SHA-1 was being used to\r
   create 64 bytes of data, it would have to be iterated 4 times\r
   (through A(4)), creating 80 bytes of output data; the last 16 bytes\r
   of the final iteration would then be discarded, leaving 64 bytes of\r
   output data.\r
\r
\r
   TLS's PRF is created by splitting the secret into two halves and\r
   using one half to generate data with P_MD5 and the other half to\r
   generate data with P_SHA-1, then exclusive-or'ing the outputs of\r
   these two expansion functions together.\r
\r
\r
   S1 and S2 are the two halves of the secret and each is the same\r
   length. S1 is taken from the first half of the secret, S2 from the\r
   second half. Their length is created by rounding up the length of the\r
   overall secret divided by two; thus, if the original secret is an odd\r
   number of bytes long, the last byte of S1 will be the same as the\r
   first byte of S2.\r
\r
\r
       L_S = length in bytes of secret;\r
       L_S1 = L_S2 = ceil(L_S / 2);\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 14] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   The secret is partitioned into two halves (with the possibility of\r
   one shared byte) as described above, S1 taking the first L_S1 bytes\r
   and S2 the last L_S2 bytes.\r
\r
\r
   The PRF is then defined as the result of mixing the two pseudorandom\r
   streams by exclusive-or'ing them together.\r
\r
\r
       PRF(secret, label, seed) = P_MD5(S1, label + seed) XOR\r
                                  P_SHA-1(S2, label + seed);\r
\r
\r
   The label is an ASCII string. It should be included in the exact form\r
   it is given without a length byte or trailing null character.  For\r
   example, the label "slithy toves" would be processed by hashing the\r
   following bytes:\r
\r
\r
       73 6C 69 74 68 79 20 74 6F 76 65 73\r
\r
\r
   Note that because MD5 produces 16 byte outputs and SHA-1 produces 20\r
   byte outputs, the boundaries of their internal iterations will not be\r
   aligned; to generate a 80 byte output will involve P_MD5 being\r
   iterated through A(5), while P_SHA-1 will only iterate through A(4).\r
\r
\r
6. The TLS Record Protocol\r
\r
\r
   The TLS Record Protocol is a layered protocol. At each layer,\r
   messages may include fields for length, description, and content.\r
   The Record Protocol takes messages to be transmitted, fragments the\r
   data into manageable blocks, optionally compresses the data, applies\r
   a MAC, encrypts, and transmits the result. Received data is\r
   decrypted, verified, decompressed, and reassembled, then delivered to\r
   higher level clients.\r
\r
\r
   Four record protocol clients are described in this document: the\r
   handshake protocol, the alert protocol, the change cipher spec\r
   protocol, and the application data protocol. In order to allow\r
   extension of the TLS protocol, additional record types can be         |\r
   supported by the record protocol. Any new record types SHOULD\r
   allocate type values immediately beyond the ContentType values for\r
   the four record types described here (see Appendix A.2). If a TLS\r
   implementation receives a record type it does not understand, it      |\r
   SHOULD just ignore it. Any protocol designed for use over TLS MUST be\r
   carefully designed to deal with all possible attacks against it.\r
   Note that because the type and length of a record are not protected   |\r
   by encryption, care SHOULD be taken to minimize the value of traffic\r
   analysis of these values.\r
\r
\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 15] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
6.1. Connection states\r
\r
\r
   A TLS connection state is the operating environment of the TLS Record\r
   Protocol. It specifies a compression algorithm, encryption algorithm,\r
   and MAC algorithm. In addition, the parameters for these algorithms\r
   are known: the MAC secret and the bulk encryption keys for the        |\r
   connection in both the read and the write directions. Logically,\r
   there are always four connection states outstanding: the current read\r
   and write states, and the pending read and write states. All records\r
   are processed under the current read and write states. The security\r
   parameters for the pending states can be set by the TLS Handshake\r
   Protocol, and the Handshake Protocol can selectively make either of\r
   the pending states current, in which case the appropriate current\r
   state is disposed of and replaced with the pending state; the pending\r
   state is then reinitialized to an empty state. It is illegal to make\r
   a state which has not been initialized with security parameters a\r
   current state. The initial current state always specifies that no\r
   encryption, compression, or MAC will be used.\r
\r
\r
   The security parameters for a TLS Connection read and write state are\r
   set by providing the following values:\r
\r
\r
   connection end\r
       Whether this entity is considered the "client" or the "server" in\r
       this connection.\r
\r
\r
   bulk encryption algorithm\r
       An algorithm to be used for bulk encryption. This specification\r
       includes the key size of this algorithm, how much of that key is\r
       secret, whether it is a block or stream cipher, the block size of\r
       the cipher (if appropriate), and whether it is considered an\r
       "export" cipher.\r
\r
\r
   MAC algorithm\r
       An algorithm to be used for message authentication. This\r
       specification includes the size of the hash which is returned by\r
       the MAC algorithm.\r
\r
\r
   compression algorithm\r
       An algorithm to be used for data compression. This specification\r
       must include all information the algorithm requires to do\r
       compression.\r
\r
\r
   master secret\r
       A 48 byte secret shared between the two peers in the connection.\r
\r
\r
   client random\r
       A 32 byte value provided by the client.\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 16] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   server random\r
       A 32 byte value provided by the server.\r
\r
\r
   These parameters are defined in the presentation language as:\r
\r
\r
       enum { server, client } ConnectionEnd;\r
\r
\r
       enum { null, rc4, rc2, des, 3des, des40 } BulkCipherAlgorithm;\r
\r
\r
       enum { stream, block } CipherType;\r
\r
\r
       enum { true, false } IsExportable;\r
\r
\r
       enum { null, md5, sha } MACAlgorithm;\r
\r
\r
       enum { null(0), (255) } CompressionMethod;\r
\r
\r
       /* The algorithms specified in CompressionMethod,\r
          BulkCipherAlgorithm, and MACAlgorithm may be added to. */\r
\r
\r
       struct {\r
           ConnectionEnd          entity;\r
           BulkCipherAlgorithm    bulk_cipher_algorithm;\r
           CipherType             cipher_type;\r
           uint8                  key_size;\r
           uint8                  key_material_length;\r
           IsExportable           is_exportable;\r
           MACAlgorithm           mac_algorithm;\r
           uint8                  hash_size;\r
           CompressionMethod      compression_algorithm;\r
           opaque                 master_secret[48];\r
           opaque                 client_random[32];\r
           opaque                 server_random[32];\r
       } SecurityParameters;\r
\r
\r
   The record layer will use the security parameters to generate the     |\r
   following four items:\r
\r
\r
       client write MAC secret\r
       server write MAC secret\r
       client write key\r
       server write key\r
\r
\r
   The client write parameters are used by the server when receiving and\r
   processing records and vice-versa. The algorithm used for generating\r
   these items from the security parameters is described in section 6.3.\r
\r
\r
   Once the security parameters have been set and the keys have been\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 17] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   generated, the connection states can be instantiated by making them   |\r
   the current states. These current states MUST be updated for each\r
   record processed. Each connection state includes the following\r
   elements:\r
\r
\r
   compression state\r
       The current state of the compression algorithm.\r
\r
\r
   cipher state\r
       The current state of the encryption algorithm. This will consist  |\r
       of the scheduled key for that connection. For stream ciphers,     |\r
       this will also contain whatever the necessary state information   |\r
       is to allow the stream to continue to encrypt or decrypt data.\r
\r
\r
   MAC secret\r
       The MAC secret for this connection as generated above.\r
\r
\r
   sequence number\r
       Each connection state contains a sequence number, which is\r
       maintained separately for read and write states. The sequence     |\r
       number MUST be set to zero whenever a connection state is made\r
       the active state. Sequence numbers are of type uint64 and may not |\r
       exceed 2^64-1. Sequence numbers do not wrap. If a TLS             |\r
       implementation would need to wrap a sequence number it must       |\r
       renegotiate instead. A sequence number is incremented after each\r
       record: specifically, the first record which is transmitted under |\r
       a particular connection state MUST use sequence number 0.\r
\r
\r
6.2. Record layer\r
\r
\r
   The TLS Record Layer receives uninterpreted data from higher layers\r
   in non-empty blocks of arbitrary size.\r
\r
\r
6.2.1. Fragmentation\r
\r
\r
   The record layer fragments information blocks into TLSPlaintext\r
   records carrying data in chunks of 2^14 bytes or less. Client message\r
   boundaries are not preserved in the record layer (i.e., multiple      |\r
   client messages of the same ContentType MAY be coalesced into a       |\r
   single TLSPlaintext record, or a single message MAY be fragmented     |\r
   across several records).                                              |\r
\r
\r
\r
       struct {\r
           uint8 major, minor;\r
       } ProtocolVersion;\r
\r
\r
       enum {\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 18] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
           change_cipher_spec(20), alert(21), handshake(22),\r
           application_data(23), (255)\r
       } ContentType;\r
\r
\r
       struct {\r
           ContentType type;\r
           ProtocolVersion version;\r
           uint16 length;\r
           opaque fragment[TLSPlaintext.length];\r
       } TLSPlaintext;\r
\r
\r
   type\r
       The higher level protocol used to process the enclosed fragment.\r
\r
\r
   version\r
       The version of the protocol being employed. This document         |\r
       describes TLS Version 1.1, which uses the version { 3, 2 }. The   |\r
       version value 3.2 is historical: TLS version 1.1 is a minor       |\r
       modification to the TLS 1.0 protocol, which was itself a minor    |\r
       modification to the SSL 3.0 protocol, which bears the version\r
       value 3.0. (See Appendix A.1).\r
\r
\r
   length\r
       The length (in bytes) of the following TLSPlaintext.fragment.\r
       The length should not exceed 2^14.\r
\r
\r
   fragment\r
       The application data. This data is transparent and treated as an\r
       independent block to be dealt with by the higher level protocol\r
       specified by the type field.\r
\r
\r
 Note: Data of different TLS Record layer content types MAY be           |\r
       interleaved. Application data is generally of lower precedence    |\r
       for transmission than other content types and therefore handshake |\r
       records may be held if application data is pending.  However,     |\r
       records MUST be delivered to the network in the same order as     |\r
       they are protected by the record layer.                           |\r
\r
\r
6.2.2. Record compression and decompression\r
\r
\r
   All records are compressed using the compression algorithm defined in\r
   the current session state. There is always an active compression\r
   algorithm; however, initially it is defined as\r
   CompressionMethod.null. The compression algorithm translates a\r
   TLSPlaintext structure into a TLSCompressed structure. Compression\r
   functions are initialized with default state information whenever a\r
   connection state is made active.\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 19] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   Compression must be lossless and may not increase the content length\r
   by more than 1024 bytes. If the decompression function encounters a\r
   TLSCompressed.fragment that would decompress to a length in excess of\r
   2^14 bytes, it should report a fatal decompression failure error.\r
\r
\r
       struct {\r
           ContentType type;       /* same as TLSPlaintext.type */\r
           ProtocolVersion version;/* same as TLSPlaintext.version */\r
           uint16 length;\r
           opaque fragment[TLSCompressed.length];\r
       } TLSCompressed;\r
\r
\r
   length\r
       The length (in bytes) of the following TLSCompressed.fragment.\r
       The length should not exceed 2^14 + 1024.\r
\r
\r
   fragment\r
       The compressed form of TLSPlaintext.fragment.\r
\r
\r
 Note: A CompressionMethod.null operation is an identity operation; no\r
       fields are altered.\r
\r
\r
   Implementation note:\r
       Decompression functions are responsible for ensuring that\r
       messages cannot cause internal buffer overflows.\r
\r
\r
6.2.3. Record payload protection\r
\r
\r
   The encryption and MAC functions translate a TLSCompressed structure\r
   into a TLSCiphertext. The decryption functions reverse the process.\r
   The MAC of the record also includes a sequence number so that\r
   missing, extra or repeated messages are detectable.\r
\r
\r
       struct {\r
           ContentType type;\r
           ProtocolVersion version;\r
           uint16 length;\r
           select (CipherSpec.cipher_type) {\r
               case stream: GenericStreamCipher;\r
               case block: GenericBlockCipher;\r
           } fragment;\r
       } TLSCiphertext;\r
\r
\r
   type\r
       The type field is identical to TLSCompressed.type.\r
\r
\r
   version\r
       The version field is identical to TLSCompressed.version.\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 20] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   length\r
       The length (in bytes) of the following TLSCiphertext.fragment.\r
       The length may not exceed 2^14 + 2048.\r
\r
\r
   fragment                                                              |\r
       The encrypted form of TLSCompressed.fragment, with the MAC.\r
\r
\r
6.2.3.1. Null or standard stream cipher\r
\r
\r
   Stream ciphers (including BulkCipherAlgorithm.null - see Appendix\r
   A.6) convert TLSCompressed.fragment structures to and from stream\r
   TLSCiphertext.fragment structures.\r
\r
\r
       stream-ciphered struct {\r
           opaque content[TLSCompressed.length];\r
           opaque MAC[CipherSpec.hash_size];\r
       } GenericStreamCipher;\r
\r
\r
   The MAC is generated as:\r
\r
\r
       HMAC_hash(MAC_write_secret, seq_num + TLSCompressed.type +\r
                     TLSCompressed.version + TLSCompressed.length +\r
                     TLSCompressed.fragment));\r
\r
\r
   where "+" denotes concatenation.\r
\r
\r
   seq_num\r
       The sequence number for this record.\r
\r
\r
   hash\r
       The hashing algorithm specified by\r
       SecurityParameters.mac_algorithm.\r
\r
\r
   Note that the MAC is computed before encryption. The stream cipher\r
   encrypts the entire block, including the MAC. For stream ciphers that\r
   do not use a synchronization vector (such as RC4), the stream cipher\r
   state from the end of one record is simply used on the subsequent\r
   packet. If the CipherSuite is TLS_NULL_WITH_NULL_NULL, encryption\r
   consists of the identity operation (i.e., the data is not encrypted\r
   and the MAC size is zero implying that no MAC is used).\r
   TLSCiphertext.length is TLSCompressed.length plus\r
   CipherSpec.hash_size.\r
\r
\r
6.2.3.2. CBC block cipher\r
\r
\r
   For block ciphers (such as RC2 or DES), the encryption and MAC\r
   functions convert TLSCompressed.fragment structures to and from block\r
   TLSCiphertext.fragment structures.\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 21] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
       block-ciphered struct {\r
           opaque IV[CipherSpec.block_length];                           |\r
           opaque content[TLSCompressed.length];\r
           opaque MAC[CipherSpec.hash_size];\r
           uint8 padding[GenericBlockCipher.padding_length];\r
           uint8 padding_length;\r
       } GenericBlockCipher;\r
\r
\r
   The MAC is generated as described in Section 6.2.3.1.\r
\r
\r
   IV                                                                    |\r
       Unlike previous versions of SSL and TLS, TLS 1.1 uses an explicit |\r
       IV in order to prevent the attacks described by [CBCATT].         |\r
       We recommend the following equivalently strong procedures.        |\r
       For clarity we use the following notation.                        |\r
\r
\r
       IV -- the transmitted value of the IV field in the                |\r
           GenericBlockCipher structure.                                 |\r
       CBC residue -- the last ciphertext block of the previous record   |\r
       mask -- the actual value which the cipher XORs with the           |\r
           plaintext prior to encryption of the first cipher block       |\r
           of the record.                                                |\r
\r
\r
       In prior versions of TLS, there was no IV field and the CBC residue|\r
       and mask were one and the same.                                   |\r
\r
\r
\r
       (1) Generate a cryptographically strong random string R of        |\r
           length CipherSpec.block_length. Place R                       |\r
           in the IV field. Set the mask to R. Thus, the first           |\r
           cipher block will be encrypted as E(R XOR Data).              |\r
\r
\r
       (2) Generate a cryptographically strong random number R of        |\r
           length CipherSpec.block_length and prepend it to the plaintext|\r
           prior to encryption. In                                       |\r
           this case either:                                             |\r
\r
\r
           (a)   The cipher may use a fixed mask such as zero.           |\r
           (b) The CBC residue from the previous record may be used      |\r
               as the mask. This preserves maximum code compatibility    |\r
            with TLS 1.0 and SSL 3. It also has the advantage that       |\r
            it does not require the ability to quickly reset the IV,     |\r
            which is known to be a   problem on some systems.            |\r
\r
\r
            In either case, the data (R || data) is fed into the         |\r
            encryption process. The first cipher block (containing       |\r
            E(mask XOR R) is placed in the IV field. The first           |\r
            block of content contains E(IV XOR data)                     |\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 22] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
       The following alternative procedure MAY be used: However, it has  |\r
       not been demonstrated to be equivalently cryptographically strong |\r
       to the above procedures. The sender prepends a fixed block F to   |\r
       the plaintext (or alternatively a block generated with a weak     |\r
       PRNG). He then encrypts as in (2) above, using the CBC residue    |\r
       from the previous block as the mask for the prepended block. Note |\r
       that in this case the mask for the first record transmitted by    |\r
       the application (the Finished) MUST be generated using a          |\r
       cryptographically strong PRNG.                                    |\r
\r
\r
       The decryption operation for all three alternatives is the same.  |\r
       The receiver decrypts the entire GenericBlockCipher structure and |\r
       then discards the first cipher block, corresponding to the IV     |\r
       component.                                                        |\r
\r
\r
   padding\r
       Padding that is added to force the length of the plaintext to be\r
       an integral multiple of the block cipher's block length. The      |\r
       padding MAY be any length up to 255 bytes long, as long as it\r
       results in the TLSCiphertext.length being an integral multiple of\r
       the block length. Lengths longer than necessary might be\r
       desirable to frustrate attacks on a protocol based on analysis of\r
       the lengths of exchanged messages. Each uint8 in the padding data |\r
       vector MUST be filled with the padding length value. The receiver |\r
       MUST check this padding and SHOULD use the bad_record_mac alert   |\r
       to indicate padding errors.\r
\r
\r
   padding_length\r
       The padding length MUST be such that the total size of the        |\r
       GenericBlockCipher structure is a multiple of the cipher's block\r
       length. Legal values range from zero to 255, inclusive. This\r
       length specifies the length of the padding field exclusive of the\r
       padding_length field itself.\r
\r
\r
   The encrypted data length (TLSCiphertext.length) is one more than the\r
   sum of TLSCompressed.length, CipherSpec.hash_size, and\r
   padding_length.\r
\r
\r
 Example: If the block length is 8 bytes, the content length\r
          (TLSCompressed.length) is 61 bytes, and the MAC length is 20   |\r
          bytes, the length before padding is 82 bytes (this does not    |\r
          include the IV, which may or may not be encrypted, as          |\r
          discussed above). Thus, the padding length modulo 8 must be\r
          equal to 6 in order to make the total length an even multiple\r
          of 8 bytes (the block length). The padding length can be 6,\r
          14, 22, and so on, through 254. If the padding length were the\r
          minimum necessary, 6, the padding would be 6 bytes, each\r
          containing the value 6.  Thus, the last 8 octets of the\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 23] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
          GenericBlockCipher before block encryption would be xx 06 06\r
          06 06 06 06 06, where xx is the last octet of the MAC.\r
\r
\r
 Note: With block ciphers in CBC mode (Cipher Block Chaining),           |\r
       it is critical that the entire plaintext of the record be known   |\r
       before any ciphertext is transmitted. Otherwise it is possible    |\r
       for the attacker to mount the attack described in [CBCATT].       |\r
\r
\r
 Implementation Note: Canvel et. al. [CBCTIME] have demonstrated a       |\r
       timing attack on CBC padding based on the time required to        |\r
       compute the MAC. In order to defend against this attack,          |\r
       implementations MUST ensure that record processing time is        |\r
       essentially the same whether or not the padding is correct.  In   |\r
       general, the best way to to do this is to compute the MAC even if |\r
       the padding is incorrect, and only then reject the packet. For    |\r
       instance, if the pad appears to be incorrect the implementation   |\r
       might assume a zero-length pad and then compute the MAC. This     |\r
       leaves a small timing channel, since MAC performance depends to   |\r
       some extent on the size of the data fragment, but it is not       |\r
       believed to be large enough to be exploitable due to the large    |\r
       block size of existing MACs and the small size of the timing      |\r
       signal.\r
\r
\r
6.3. Key calculation\r
\r
\r
   The Record Protocol requires an algorithm to generate keys, and MAC   |\r
   secrets from the security parameters provided by the handshake\r
   protocol.\r
\r
\r
   The master secret is hashed into a sequence of secure bytes, which    |\r
   are assigned to the MAC secrets and keys required by the current\r
   connection state (see Appendix A.6). CipherSpecs require a client\r
   write MAC secret, a server write MAC secret, a client write key, and  |\r
   a server write key, which are generated from the master secret in     |\r
   that order. Unused values are empty.\r
\r
\r
   When generating keys and MAC secrets, the master secret is used as an\r
   entropy source, and the random values provide unencrypted salt        |\r
   material for exportable ciphers.\r
\r
\r
   To generate the key material, compute\r
\r
\r
       key_block = PRF(SecurityParameters.master_secret,\r
                          "key expansion",\r
                          SecurityParameters.server_random +\r
                          SecurityParameters.client_random);\r
\r
\r
   until enough output has been generated. Then the key_block is\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 24] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   partitioned as follows:\r
\r
\r
       client_write_MAC_secret[SecurityParameters.hash_size]\r
       server_write_MAC_secret[SecurityParameters.hash_size]\r
       client_write_key[SecurityParameters.key_material_length]\r
       server_write_key[SecurityParameters.key_material_length]\r
\r
\r
\r
   Implementation note:\r
       The cipher spec which is defined in this document which requires\r
       the most material is 3DES_EDE_CBC_SHA: it requires 2 x 24 byte    |\r
       keys, 2 x 20 byte MAC secrets, for a total 88 bytes of key        |\r
       material.\r
\r
\r
   Exportable encryption algorithms (for which CipherSpec.is_exportable\r
   is true) require additional processing as follows to derive their\r
   final write keys:\r
\r
\r
       final_client_write_key =\r
       PRF(SecurityParameters.client_write_key,\r
                                  "client write key",\r
                                  SecurityParameters.client_random +\r
                                  SecurityParameters.server_random);\r
       final_server_write_key =\r
       PRF(SecurityParameters.server_write_key,\r
                                  "server write key",\r
                                  SecurityParameters.client_random +\r
                                  SecurityParameters.server_random);\r
\r
\r
6.3.1. Export key generation example\r
\r
\r
   TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5 requires five random bytes for\r
   each of the two encryption keys and 16 bytes for each of the MAC\r
   keys, for a total of 42 bytes of key material. The PRF output is\r
   stored in the key_block. The key_block is partitioned, and the write\r
   keys are salted because this is an exportable encryption algorithm.\r
\r
\r
       key_block               = PRF(master_secret,\r
                                     "key expansion",\r
                                     server_random +\r
                                     client_random)[0..41]\r
       client_write_MAC_secret = key_block[0..15]\r
       server_write_MAC_secret = key_block[16..31]\r
       client_write_key        = key_block[32..36]\r
       server_write_key        = key_block[37..41]\r
       final_client_write_key  = PRF(client_write_key,\r
                                     "client write key",\r
                                     client_random +\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 25] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
                                     server_random)[0..15]\r
       final_server_write_key  = PRF(server_write_key,\r
                                     "server write key",\r
                                     client_random +\r
                                     server_random)[0..15]\r
\r
\r
\r
7. The TLS Handshake Protocol\r
\r
\r
   The TLS Handshake Protocol consists of a suite of three sub-protocols\r
   which are used to allow peers to agree upon security parameters for\r
   the record layer, authenticate themselves, instantiate negotiated\r
   security parameters, and report error conditions to each other.\r
\r
\r
   The Handshake Protocol is responsible for negotiating a session,\r
   which consists of the following items:\r
\r
\r
   session identifier\r
       An arbitrary byte sequence chosen by the server to identify an\r
       active or resumable session state.\r
\r
\r
   peer certificate\r
       X509v3 [X509] certificate of the peer. This element of the state\r
       may be null.\r
\r
\r
   compression method\r
       The algorithm used to compress data prior to encryption.\r
\r
\r
   cipher spec\r
       Specifies the bulk data encryption algorithm (such as null, DES,\r
       etc.) and a MAC algorithm (such as MD5 or SHA). It also defines\r
       cryptographic attributes such as the hash_size. (See Appendix A.6\r
       for formal definition)\r
\r
\r
   master secret\r
       48-byte secret shared between the client and server.\r
\r
\r
   is resumable\r
       A flag indicating whether the session can be used to initiate new\r
       connections.\r
\r
\r
   These items are then used to create security parameters for use by\r
   the Record Layer when protecting application data. Many connections\r
   can be instantiated using the same session through the resumption\r
   feature of the TLS Handshake Protocol.\r
\r
\r
7.1. Change cipher spec protocol\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 26] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
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\r
\r
   The change cipher spec protocol exists to signal transitions in\r
   ciphering strategies. The protocol consists of a single message,\r
   which is encrypted and compressed under the current (not the pending)\r
   connection state. The message consists of a single byte of value 1.\r
\r
\r
       struct {\r
           enum { change_cipher_spec(1), (255) } type;\r
       } ChangeCipherSpec;\r
\r
\r
   The change cipher spec message is sent by both the client and server\r
   to notify the receiving party that subsequent records will be\r
   protected under the newly negotiated CipherSpec and keys. Reception\r
   of this message causes the receiver to instruct the Record Layer to\r
   immediately copy the read pending state into the read current state.  |\r
   Immediately after sending this message, the sender MUST instruct the\r
   record layer to make the write pending state the write active state.\r
   (See section 6.1.) The change cipher spec message is sent during the\r
   handshake after the security parameters have been agreed upon, but\r
   before the verifying finished message is sent (see section 7.4.9).\r
\r
\r
7.2. Alert protocol\r
\r
\r
   One of the content types supported by the TLS Record layer is the\r
   alert type. Alert messages convey the severity of the message and a\r
   description of the alert. Alert messages with a level of fatal result\r
   in the immediate termination of the connection. In this case, other\r
   connections corresponding to the session may continue, but the        |\r
   session identifier MUST be invalidated, preventing the failed session\r
   from being used to establish new connections. Like other messages,\r
   alert messages are encrypted and compressed, as specified by the\r
   current connection state.\r
\r
\r
       enum { warning(1), fatal(2), (255) } AlertLevel;\r
\r
\r
       enum {\r
           close_notify(0),\r
           unexpected_message(10),\r
           bad_record_mac(20),\r
           decryption_failed(21),\r
           record_overflow(22),\r
           decompression_failure(30),\r
           handshake_failure(40),\r
           no_certificate_RESERVED (41),                                 |\r
           bad_certificate(42),\r
           unsupported_certificate(43),\r
           certificate_revoked(44),\r
           certificate_expired(45),\r
           certificate_unknown(46),\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 27] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
           illegal_parameter(47),\r
           unknown_ca(48),\r
           access_denied(49),\r
           decode_error(50),\r
           decrypt_error(51),\r
           export_restriction(60),\r
           protocol_version(70),\r
           insufficient_security(71),\r
           internal_error(80),\r
           user_canceled(90),\r
           no_renegotiation(100),\r
           (255)\r
       } AlertDescription;\r
\r
\r
       struct {\r
           AlertLevel level;\r
           AlertDescription description;\r
       } Alert;\r
\r
\r
7.2.1. Closure alerts\r
\r
\r
   The client and the server must share knowledge that the connection is\r
   ending in order to avoid a truncation attack. Either party may\r
   initiate the exchange of closing messages.\r
\r
\r
   close_notify\r
       This message notifies the recipient that the sender will not send |\r
       any more messages on this connection. The session MUST not be     |\r
       resumed if any connection is terminated without proper\r
       close_notify messages with level equal to warning.\r
\r
\r
   Either party may initiate a close by sending a close_notify alert.\r
   Any data received after a closure alert is ignored.\r
\r
\r
   Unless some other fatal alert has been transmitted, each party is     |\r
   required to send a close_notify alert before closing the write side   |\r
   of the connection. The other party MUST respond with a close_notify   |\r
   alert of its own and close down the connection immediately,\r
   discarding any pending writes. It is not required for the initiator\r
   of the close to wait for the responding close_notify alert before\r
   closing the read side of the connection.\r
\r
\r
   If the application protocol using TLS provides that any data may be\r
   carried over the underlying transport after the TLS connection is\r
   closed, the TLS implementation must receive the responding\r
   close_notify alert before indicating to the application layer that\r
   the TLS connection has ended. If the application protocol will not\r
   transfer any additional data, but will only close the underlying      |\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 28] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   transport connection, then the implementation MAY choose to close the\r
   transport without waiting for the responding close_notify. No part of\r
   this standard should be taken to dictate the manner in which a usage\r
   profile for TLS manages its data transport, including when\r
   connections are opened or closed.\r
\r
\r
   NB: It is assumed that closing a connection reliably delivers\r
       pending data before destroying the transport.\r
\r
\r
7.2.2. Error alerts\r
\r
\r
   Error handling in the TLS Handshake protocol is very simple. When an\r
   error is detected, the detecting party sends a message to the other\r
   party. Upon transmission or receipt of an fatal alert message, both   |\r
   parties immediately close the connection. Servers and clients MUST    |\r
   forget any session-identifiers, keys, and secrets associated with a\r
   failed connection. The following error alerts are defined:\r
\r
\r
   unexpected_message\r
       An inappropriate message was received. This alert is always fatal\r
       and should never be observed in communication between proper\r
       implementations.\r
\r
\r
   bad_record_mac\r
       This alert is returned if a record is received with an incorrect  |\r
       MAC. This alert also SHOULD be returned if a TLSCiphertext        |\r
       decrypted in an invalid way: either it wasn't an even multiple of |\r
       the block length, or its padding values, when checked, weren't    |\r
       correct. This message is always fatal.\r
\r
\r
   decryption_failed\r
       This alert MAY be returned if a TLSCiphertext decrypted in an     |\r
       invalid way: either it wasn't an even multiple of the block       |\r
       length, or its padding values, when checked, weren't correct.     |\r
       This message is always fatal.                                     |\r
\r
\r
       NB: Differentiating between bad_record_mac and decryption_failed  |\r
       alerts may permit certain attacks against CBC mode as used in TLS |\r
       [CBCATT]. It is preferable to uniformly use the bad_record_mac    |\r
       alert to hide the specific type of the error.                     |\r
\r
\r
\r
   record_overflow\r
       A TLSCiphertext record was received which had a length more than\r
       2^14+2048 bytes, or a record decrypted to a TLSCompressed record\r
       with more than 2^14+1024 bytes. This message is always fatal.\r
\r
\r
   decompression_failure\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 29] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
       The decompression function received improper input (e.g. data\r
       that would expand to excessive length). This message is always\r
       fatal.\r
\r
\r
   handshake_failure\r
       Reception of a handshake_failure alert message indicates that the\r
       sender was unable to negotiate an acceptable set of security\r
       parameters given the options available. This is a fatal error.\r
\r
\r
   no_certificate_RESERVED                                               |\r
       This alert was used in SSLv3 but not in TLS. It should not be     |\r
       sent by compliant implementations.                                |\r
\r
\r
   bad_certificate\r
       A certificate was corrupt, contained signatures that did not\r
       verify correctly, etc.\r
\r
\r
   unsupported_certificate\r
       A certificate was of an unsupported type.\r
\r
\r
   certificate_revoked\r
       A certificate was revoked by its signer.\r
\r
\r
   certificate_expired\r
       A certificate has expired or is not currently valid.\r
\r
\r
   certificate_unknown\r
       Some other (unspecified) issue arose in processing the\r
       certificate, rendering it unacceptable.\r
\r
\r
   illegal_parameter\r
       A field in the handshake was out of range or inconsistent with\r
       other fields. This is always fatal.\r
\r
\r
   unknown_ca\r
       A valid certificate chain or partial chain was received, but the\r
       certificate was not accepted because the CA certificate could not |\r
       be located or couldn't be matched with a known, trusted CA.  This\r
       message is always fatal.\r
\r
\r
   access_denied\r
       A valid certificate was received, but when access control was\r
       applied, the sender decided not to proceed with negotiation.\r
       This message is always fatal.\r
\r
\r
   decode_error\r
       A message could not be decoded because some field was out of the\r
       specified range or the length of the message was incorrect. This\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 30] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
       message is always fatal.\r
\r
\r
   decrypt_error\r
       A handshake cryptographic operation failed, including being\r
       unable to correctly verify a signature, decrypt a key exchange,\r
       or validate a finished message.\r
\r
\r
   export_restriction\r
       A negotiation not in compliance with export restrictions was\r
       detected; for example, attempting to transfer a 1024 bit\r
       ephemeral RSA key for the RSA_EXPORT handshake method. This\r
       message is always fatal.\r
\r
\r
   protocol_version\r
       The protocol version the client has attempted to negotiate is\r
       recognized, but not supported. (For example, old protocol\r
       versions might be avoided for security reasons). This message is\r
       always fatal.\r
\r
\r
   insufficient_security\r
       Returned instead of handshake_failure when a negotiation has\r
       failed specifically because the server requires ciphers more\r
       secure than those supported by the client. This message is always\r
       fatal.\r
\r
\r
   internal_error\r
       An internal error unrelated to the peer or the correctness of the\r
       protocol makes it impossible to continue (such as a memory\r
       allocation failure). This message is always fatal.\r
\r
\r
   user_canceled\r
       This handshake is being canceled for some reason unrelated to a\r
       protocol failure. If the user cancels an operation after the\r
       handshake is complete, just closing the connection by sending a\r
       close_notify is more appropriate. This alert should be followed\r
       by a close_notify. This message is generally a warning.\r
\r
\r
   no_renegotiation\r
       Sent by the client in response to a hello request or by the\r
       server in response to a client hello after initial handshaking.\r
       Either of these would normally lead to renegotiation; when that\r
       is not appropriate, the recipient should respond with this alert;\r
       at that point, the original requester can decide whether to\r
       proceed with the connection. One case where this would be\r
       appropriate would be where a server has spawned a process to\r
       satisfy a request; the process might receive security parameters\r
       (key length, authentication, etc.) at startup and it might be\r
       difficult to communicate changes to these parameters after that\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 31] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
       point. This message is always a warning.\r
\r
\r
   For all errors where an alert level is not explicitly specified, the  |\r
   sending party MAY determine at its discretion whether this is a fatal\r
   error or not; if an alert with a level of warning is received, the\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 32] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   receiving party MAY decide at its discretion whether to treat this as |\r
   a fatal error or not. However, all messages which are transmitted     |\r
   with a level of fatal MUST be treated as fatal messages.\r
\r
\r
7.3. Handshake Protocol overview\r
\r
\r
   The cryptographic parameters of the session state are produced by the\r
   TLS Handshake Protocol, which operates on top of the TLS Record\r
   Layer. When a TLS client and server first start communicating, they\r
   agree on a protocol version, select cryptographic algorithms,\r
   optionally authenticate each other, and use public-key encryption\r
   techniques to generate shared secrets.\r
\r
\r
   The TLS Handshake Protocol involves the following steps:\r
\r
\r
     - - Exchange hello messages to agree on algorithms, exchange random\r
       values, and check for session resumption.\r
\r
\r
     - - Exchange the necessary cryptographic parameters to allow the\r
       client and server to agree on a premaster secret.\r
\r
\r
     - - Exchange certificates and cryptographic information to allow\r
       the client and server to authenticate themselves.\r
\r
\r
     - - Generate a master secret from the premaster secret and\r
       exchanged random values.\r
\r
\r
     - - Provide security parameters to the record layer.\r
\r
\r
     - - Allow the client and server to verify that their peer has\r
       calculated the same security parameters and that the handshake\r
       occurred without tampering by an attacker.\r
\r
\r
   Note that higher layers should not be overly reliant on TLS always\r
   negotiating the strongest possible connection between two peers:\r
   there are a number of ways a man in the middle attacker can attempt\r
   to make two entities drop down to the least secure method they\r
   support. The protocol has been designed to minimize this risk, but\r
   there are still attacks available: for example, an attacker could\r
   block access to the port a secure service runs on, or attempt to get\r
   the peers to negotiate an unauthenticated connection. The fundamental\r
   rule is that higher levels must be cognizant of what their security\r
   requirements are and never transmit information over a channel less\r
   secure than what they require. The TLS protocol is secure, in that\r
   any cipher suite offers its promised level of security: if you\r
   negotiate 3DES with a 1024 bit RSA key exchange with a host whose\r
   certificate you have verified, you can expect to be that secure.\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 33] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   However, you SHOULD never send data over a link encrypted with 40 bit |\r
   security unless you feel that data is worth no more than the effort\r
   required to break that encryption.\r
\r
\r
   These goals are achieved by the handshake protocol, which can be\r
   summarized as follows: The client sends a client hello message to\r
   which the server must respond with a server hello message, or else a\r
   fatal error will occur and the connection will fail. The client hello\r
   and server hello are used to establish security enhancement\r
   capabilities between client and server. The client hello and server\r
   hello establish the following attributes: Protocol Version, Session\r
   ID, Cipher Suite, and Compression Method. Additionally, two random\r
   values are generated and exchanged: ClientHello.random and\r
   ServerHello.random.\r
\r
\r
   The actual key exchange uses up to four messages: the server\r
   certificate, the server key exchange, the client certificate, and the\r
   client key exchange. New key exchange methods can be created by\r
   specifying a format for these messages and defining the use of the\r
   messages to allow the client and server to agree upon a shared        |\r
   secret. This secret MUST be quite long; currently defined key\r
   exchange methods exchange secrets which range from 48 to 128 bytes in\r
   length.\r
\r
\r
   Following the hello messages, the server will send its certificate,\r
   if it is to be authenticated. Additionally, a server key exchange\r
   message may be sent, if it is required (e.g. if their server has no\r
   certificate, or if its certificate is for signing only). If the\r
   server is authenticated, it may request a certificate from the\r
   client, if that is appropriate to the cipher suite selected. Now the\r
   server will send the server hello done message, indicating that the\r
   hello-message phase of the handshake is complete. The server will\r
   then wait for a client response. If the server has sent a certificate\r
   request message, the client must send the certificate message. The\r
   client key exchange message is now sent, and the content of that\r
   message will depend on the public key algorithm selected between the\r
   client hello and the server hello. If the client has sent a\r
   certificate with signing ability, a digitally-signed certificate\r
   verify message is sent to explicitly verify the certificate.\r
\r
\r
   At this point, a change cipher spec message is sent by the client,\r
   and the client copies the pending Cipher Spec into the current Cipher\r
   Spec. The client then immediately sends the finished message under\r
   the new algorithms, keys, and secrets. In response, the server will\r
   send its own change cipher spec message, transfer the pending to the\r
   current Cipher Spec, and send its finished message under the new\r
\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 34] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   Cipher Spec. At this point, the handshake is complete and the client\r
   and server may begin to exchange application layer data. (See flow\r
   chart below.)\r
\r
\r
      Client                                               Server\r
\r
\r
      ClientHello                  -------->\r
                                                      ServerHello\r
                                                     Certificate*\r
                                               ServerKeyExchange*\r
                                              CertificateRequest*\r
                                   <--------      ServerHelloDone\r
      Certificate*\r
      ClientKeyExchange\r
      CertificateVerify*\r
      [ChangeCipherSpec]\r
      Finished                     -------->\r
                                               [ChangeCipherSpec]\r
                                   <--------             Finished\r
      Application Data             <------->     Application Data\r
\r
\r
             Fig. 1 - Message flow for a full handshake\r
\r
\r
   * Indicates optional or situation-dependent messages that are not\r
   always sent.\r
\r
\r
  Note: To help avoid pipeline stalls, ChangeCipherSpec is an\r
       independent TLS Protocol content type, and is not actually a TLS\r
       handshake message.\r
\r
\r
   When the client and server decide to resume a previous session or\r
   duplicate an existing session (instead of negotiating new security\r
   parameters) the message flow is as follows:\r
\r
\r
   The client sends a ClientHello using the Session ID of the session to\r
   be resumed. The server then checks its session cache for a match.  If\r
   a match is found, and the server is willing to re-establish the\r
   connection under the specified session state, it will send a\r
   ServerHello with the same Session ID value. At this point, both       |\r
   client and server MUST send change cipher spec messages and proceed\r
   directly to finished messages. Once the re-establishment is complete, |\r
   the client and server MAY begin to exchange application layer data.\r
   (See flow chart below.) If a Session ID match is not found, the\r
   server generates a new session ID and the TLS client and server\r
   perform a full handshake.\r
\r
\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 35] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
      Client                                                Server\r
\r
\r
      ClientHello                   -------->\r
                                                       ServerHello\r
                                                [ChangeCipherSpec]\r
                                    <--------             Finished\r
      [ChangeCipherSpec]\r
      Finished                      -------->\r
      Application Data              <------->     Application Data\r
\r
\r
          Fig. 2 - Message flow for an abbreviated handshake\r
\r
\r
   The contents and significance of each message will be presented in\r
   detail in the following sections.\r
\r
\r
7.4. Handshake protocol\r
\r
\r
   The TLS Handshake Protocol is one of the defined higher level clients\r
   of the TLS Record Protocol. This protocol is used to negotiate the\r
   secure attributes of a session. Handshake messages are supplied to\r
   the TLS Record Layer, where they are encapsulated within one or more\r
   TLSPlaintext structures, which are processed and transmitted as\r
   specified by the current active session state.\r
\r
\r
       enum {\r
           hello_request(0), client_hello(1), server_hello(2),\r
           certificate(11), server_key_exchange (12),\r
           certificate_request(13), server_hello_done(14),\r
           certificate_verify(15), client_key_exchange(16),\r
           finished(20), (255)\r
       } HandshakeType;\r
\r
\r
       struct {\r
           HandshakeType msg_type;    /* handshake type */\r
           uint24 length;             /* bytes in message */\r
           select (HandshakeType) {\r
               case hello_request:       HelloRequest;\r
               case client_hello:        ClientHello;\r
               case server_hello:        ServerHello;\r
               case certificate:         Certificate;\r
               case server_key_exchange: ServerKeyExchange;\r
               case certificate_request: CertificateRequest;\r
               case server_hello_done:   ServerHelloDone;\r
               case certificate_verify:  CertificateVerify;\r
               case client_key_exchange: ClientKeyExchange;\r
               case finished:            Finished;\r
           } body;\r
       } Handshake;\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 36] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   The handshake protocol messages are presented below in the order they |\r
   MUST be sent; sending handshake messages in an unexpected order\r
   results in a fatal error. Unneeded handshake messages can be omitted,\r
   however. Note one exception to the ordering: the Certificate message\r
   is used twice in the handshake (from server to client, then from\r
   client to server), but described only in its first position. The one\r
   message which is not bound by these ordering rules is the Hello       |\r
   Request message, which can be sent at any time, but which should be\r
   ignored by the client if it arrives in the middle of a handshake.\r
\r
\r
7.4.1. Hello messages\r
\r
\r
   The hello phase messages are used to exchange security enhancement\r
   capabilities between the client and server. When a new session\r
   begins, the Record Layer's connection state encryption, hash, and\r
   compression algorithms are initialized to null. The current\r
   connection state is used for renegotiation messages.\r
\r
\r
7.4.1.1. Hello request\r
\r
\r
   When this message will be sent:\r
       The hello request message MAY be sent by the server at any time.  |\r
\r
\r
   Meaning of this message:\r
       Hello request is a simple notification that the client should\r
       begin the negotiation process anew by sending a client hello\r
       message when convenient. This message will be ignored by the\r
       client if the client is currently negotiating a session. This\r
       message may be ignored by the client if it does not wish to\r
       renegotiate a session, or the client may, if it wishes, respond\r
       with a no_renegotiation alert. Since handshake messages are\r
       intended to have transmission precedence over application data,\r
       it is expected that the negotiation will begin before no more\r
       than a few records are received from the client. If the server\r
       sends a hello request but does not receive a client hello in\r
       response, it may close the connection with a fatal alert.\r
\r
\r
   After sending a hello request, servers SHOULD not repeat the request  |\r
   until the subsequent handshake negotiation is complete.\r
\r
\r
   Structure of this message:\r
       struct { } HelloRequest;\r
\r
\r
 Note: This message MUST NOT be included in the message hashes which are |\r
       maintained throughout the handshake and used in the finished\r
       messages and the certificate verify message.\r
\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 37] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
7.4.1.2. Client hello\r
\r
\r
   When this message will be sent:\r
       When a client first connects to a server it is required to send\r
       the client hello as its first message. The client can also send a\r
       client hello in response to a hello request or on its own\r
       initiative in order to renegotiate the security parameters in an\r
       existing connection.\r
\r
\r
       Structure of this message:\r
           The client hello message includes a random structure, which is\r
           used later in the protocol.\r
\r
\r
           struct {\r
              uint32 gmt_unix_time;\r
              opaque random_bytes[28];\r
           } Random;\r
\r
\r
       gmt_unix_time\r
       The current time and date in standard UNIX 32-bit format (seconds\r
       since the midnight starting Jan 1, 1970, GMT) according to the\r
       sender's internal clock. Clocks are not required to be set\r
       correctly by the basic TLS Protocol; higher level or application\r
       protocols may define additional requirements.\r
\r
\r
   random_bytes\r
       28 bytes generated by a secure random number generator.\r
\r
\r
   The client hello message includes a variable length session           |\r
   identifier. If not empty, the value identifies a session between the\r
   same client and server whose security parameters the client wishes to |\r
   reuse. The session identifier MAY be from an earlier connection, this\r
   connection, or another currently active connection. The second option\r
   is useful if the client only wishes to update the random structures\r
   and derived values of a connection, while the third option makes it\r
   possible to establish several independent secure connections without\r
   repeating the full handshake protocol. These independent connections\r
   may occur sequentially or simultaneously; a SessionID becomes valid\r
   when the handshake negotiating it completes with the exchange of\r
   Finished messages and persists until removed due to aging or because\r
   a fatal error was encountered on a connection associated with the\r
   session. The actual contents of the SessionID are defined by the\r
   server.\r
\r
\r
       opaque SessionID<0..32>;\r
\r
\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 38] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   Warning:\r
       Because the SessionID is transmitted without encryption or        |\r
       immediate MAC protection, servers MUST not place confidential\r
       information in session identifiers or let the contents of fake\r
       session identifiers cause any breach of security. (Note that the\r
       content of the handshake as a whole, including the SessionID, is\r
       protected by the Finished messages exchanged at the end of the\r
       handshake.)\r
\r
\r
   The CipherSuite list, passed from the client to the server in the     |\r
   client hello message, contains the combinations of cryptographic\r
   algorithms supported by the client in order of the client's\r
   preference (favorite choice first). Each CipherSuite defines a key\r
   exchange algorithm, a bulk encryption algorithm (including secret key\r
   length) and a MAC algorithm. The server will select a cipher suite\r
   or, if no acceptable choices are presented, return a handshake\r
   failure alert and close the connection.\r
\r
\r
       uint8 CipherSuite[2];    /* Cryptographic suite selector */\r
\r
\r
   The client hello includes a list of compression algorithms supported\r
   by the client, ordered according to the client's preference.\r
\r
\r
       enum { null(0), (255) } CompressionMethod;\r
\r
\r
       struct {\r
           ProtocolVersion client_version;\r
           Random random;\r
           SessionID session_id;\r
           CipherSuite cipher_suites<2..2^16-1>;\r
           CompressionMethod compression_methods<1..2^8-1>;\r
       } ClientHello;\r
\r
\r
   client_version\r
       The version of the TLS protocol by which the client wishes to     |\r
       communicate during this session. This SHOULD be the latest\r
       (highest valued) version supported by the client. For this        |\r
       version of the specification, the version will be 3.2 (See\r
       Appendix E for details about backward compatibility).\r
\r
\r
   random\r
       A client-generated random structure.\r
\r
\r
   session_id\r
       The ID of a session the client wishes to use for this connection.\r
       This field should be empty if no session_id is available or the\r
       client wishes to generate new security parameters.\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 39] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   cipher_suites\r
       This is a list of the cryptographic options supported by the\r
       client, with the client's first preference first. If the\r
       session_id field is not empty (implying a session resumption      |\r
       request) this vector MUST include at least the cipher_suite from\r
       that session. Values are defined in Appendix A.5.\r
\r
\r
   compression_methods\r
       This is a list of the compression methods supported by the\r
       client, sorted by client preference. If the session_id field is\r
       not empty (implying a session resumption request) it must include\r
       the compression_method from that session. This vector must\r
       contain, and all implementations must support,\r
       CompressionMethod.null. Thus, a client and server will always be\r
       able to agree on a compression method.\r
\r
\r
   After sending the client hello message, the client waits for a server\r
   hello message. Any other handshake message returned by the server\r
   except for a hello request is treated as a fatal error.\r
\r
\r
   Forward compatibility note:\r
       In the interests of forward compatibility, it is permitted for a\r
       client hello message to include extra data after the compression  |\r
       methods. This data MUST be included in the handshake hashes, but\r
       must otherwise be ignored. This is the only handshake message for\r
       which this is legal; for all other messages, the amount of data   |\r
       in the message MUST match the description of the message\r
       precisely.\r
\r
\r
Note: For the intended use of trailing data in the ClientHello, see RFC  |\r
       3546 [TLSEXT].                                                    |\r
\r
\r
7.4.1.3. Server hello\r
\r
\r
   When this message will be sent:\r
       The server will send this message in response to a client hello\r
       message when it was able to find an acceptable set of algorithms.\r
       If it cannot find such a match, it will respond with a handshake\r
       failure alert.\r
\r
\r
   Structure of this message:\r
       struct {\r
           ProtocolVersion server_version;\r
           Random random;\r
           SessionID session_id;\r
           CipherSuite cipher_suite;\r
           CompressionMethod compression_method;\r
       } ServerHello;\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 40] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   server_version\r
       This field will contain the lower of that suggested by the client\r
       in the client hello and the highest supported by the server. For\r
       this version of the specification, the version is 3.2 (See        |\r
       Appendix E for details about backward compatibility).\r
\r
\r
   random\r
       This structure is generated by the server and MUST be             |\r
       independently generated from the ClientHello.random.\r
\r
\r
   session_id\r
       This is the identity of the session corresponding to this\r
       connection. If the ClientHello.session_id was non-empty, the\r
       server will look in its session cache for a match. If a match is\r
       found and the server is willing to establish the new connection\r
       using the specified session state, the server will respond with\r
       the same value as was supplied by the client. This indicates a\r
       resumed session and dictates that the parties must proceed\r
       directly to the finished messages. Otherwise this field will\r
       contain a different value identifying the new session. The server\r
       may return an empty session_id to indicate that the session will\r
       not be cached and therefore cannot be resumed. If a session is\r
       resumed, it must be resumed using the same cipher suite it was\r
       originally negotiated with.\r
\r
\r
   cipher_suite\r
       The single cipher suite selected by the server from the list in\r
       ClientHello.cipher_suites. For resumed sessions this field is the\r
       value from the state of the session being resumed.\r
\r
\r
   compression_method                                                    |\r
       The single compression algorithm selected by the server from the\r
       list in ClientHello.compression_methods. For resumed sessions\r
       this field is the value from the resumed session state.\r
\r
\r
7.4.2. Server certificate\r
\r
\r
   When this message will be sent:\r
       The server MUST send a certificate whenever the agreed-upon key   |\r
       exchange method is not an anonymous one. This message will always\r
       immediately follow the server hello message.\r
\r
\r
   Meaning of this message:\r
       The certificate type MUST be appropriate for the selected cipher  |\r
       suite's key exchange algorithm, and is generally an X.509v3       |\r
       certificate. It MUST contain a key which matches the key exchange\r
       method, as follows. Unless otherwise specified, the signing\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 41] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
       algorithm for the certificate MUST be the same as the algorithm   |\r
       for the certificate key. Unless otherwise specified, the public   |\r
       key MAY be of any length.\r
\r
\r
       Key Exchange Algorithm  Certificate Key Type\r
\r
\r
       RSA                     RSA public key; the certificate MUST      |\r
                               allow the key to be used for encryption.\r
\r
\r
       RSA_EXPORT              RSA public key of length greater than\r
                               512 bits which can be used for signing,\r
                               or a key of 512 bits or shorter which\r
                               can be used for encryption.               |\r
\r
\r
       DHE_DSS                 DSS public key.\r
\r
\r
       DHE_DSS_EXPORT          DSS public key.\r
\r
\r
       DHE_RSA                 RSA public key which can be used for\r
                               signing.\r
\r
\r
       DHE_RSA_EXPORT          RSA public key which can be used for\r
                               signing.\r
\r
\r
       DH_DSS                  Diffie-Hellman key. The algorithm used\r
                               to sign the certificate MUST be DSS.      |\r
\r
\r
       DH_RSA                  Diffie-Hellman key. The algorithm used\r
                               to sign the certificate MUST be RSA.      |\r
\r
\r
   All certificate profiles, key and cryptographic formats are defined\r
   by the IETF PKIX working group [PKIX]. When a key usage extension is  |\r
   present, the digitalSignature bit MUST be set for the key to be\r
   eligible for signing, as described above, and the keyEncipherment bit |\r
   MUST be present to allow encryption, as described above. The\r
   keyAgreement bit must be set on Diffie-Hellman certificates.\r
\r
\r
   As CipherSuites which specify new key exchange methods are specified\r
   for the TLS Protocol, they will imply certificate format and the\r
   required encoded keying information.\r
\r
\r
   Structure of this message:\r
       opaque ASN.1Cert<1..2^24-1>;\r
\r
\r
       struct {\r
           ASN.1Cert certificate_list<0..2^24-1>;\r
       } Certificate;\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 42] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   certificate_list\r
       This is a sequence (chain) of X.509v3 certificates. The sender's\r
       certificate must come first in the list. Each following\r
       certificate must directly certify the one preceding it. Because\r
       certificate validation requires that root keys be distributed\r
       independently, the self-signed certificate which specifies the\r
       root certificate authority may optionally be omitted from the\r
       chain, under the assumption that the remote end must already\r
       possess it in order to validate it in any case.\r
\r
\r
   The same message type and structure will be used for the client's     |\r
   response to a certificate request message. Note that a client MAY\r
   send no certificates if it does not have an appropriate certificate\r
   to send in response to the server's authentication request.\r
\r
\r
 Note: PKCS #7 [PKCS7] is not used as the format for the certificate\r
       vector because PKCS #6 [PKCS6] extended certificates are not\r
       used. Also PKCS #7 defines a SET rather than a SEQUENCE, making\r
       the task of parsing the list more difficult.\r
\r
\r
7.4.3. Server key exchange message\r
\r
\r
   When this message will be sent:\r
       This message will be sent immediately after the server\r
       certificate message (or the server hello message, if this is an\r
       anonymous negotiation).\r
\r
\r
       The server key exchange message is sent by the server only when\r
       the server certificate message (if sent) does not contain enough\r
       data to allow the client to exchange a premaster secret. This is\r
       true for the following key exchange methods:\r
\r
\r
           RSA_EXPORT (if the public key in the server certificate is\r
           longer than 512 bits)\r
           DHE_DSS\r
           DHE_DSS_EXPORT\r
           DHE_RSA\r
           DHE_RSA_EXPORT\r
           DH_anon\r
\r
\r
       It is not legal to send the server key exchange message for the\r
       following key exchange methods:\r
\r
\r
           RSA\r
           RSA_EXPORT (when the public key in the server certificate is\r
           less than or equal to 512 bits in length)\r
           DH_DSS\r
           DH_RSA\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 43] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   Meaning of this message:\r
       This message conveys cryptographic information to allow the\r
       client to communicate the premaster secret: either an RSA public\r
       key to encrypt the premaster secret with, or a Diffie-Hellman\r
       public key with which the client can complete a key exchange\r
       (with the result being the premaster secret.)\r
\r
\r
   As additional CipherSuites are defined for TLS which include new key  |\r
   exchange algorithms, the server key exchange message will be sent if\r
   and only if the certificate type associated with the key exchange\r
   algorithm does not provide enough information for the client to\r
   exchange a premaster secret.\r
\r
\r
 Note: According to current US export law, RSA moduli larger than 512\r
       bits may not be used for key exchange in software exported from\r
       the US. With this message, the larger RSA keys encoded in\r
       certificates may be used to sign temporary shorter RSA keys for\r
       the RSA_EXPORT key exchange method.\r
\r
\r
   Structure of this message:\r
       enum { rsa, diffie_hellman } KeyExchangeAlgorithm;\r
\r
\r
       struct {\r
           opaque rsa_modulus<1..2^16-1>;\r
           opaque rsa_exponent<1..2^16-1>;\r
       } ServerRSAParams;\r
\r
\r
       rsa_modulus\r
           The modulus of the server's temporary RSA key.\r
\r
\r
       rsa_exponent\r
           The public exponent of the server's temporary RSA key.\r
\r
\r
       struct {\r
           opaque dh_p<1..2^16-1>;\r
           opaque dh_g<1..2^16-1>;\r
           opaque dh_Ys<1..2^16-1>;\r
       } ServerDHParams;     /* Ephemeral DH parameters */\r
\r
\r
       dh_p\r
           The prime modulus used for the Diffie-Hellman operation.\r
\r
\r
       dh_g\r
           The generator used for the Diffie-Hellman operation.\r
\r
\r
       dh_Ys\r
           The server's Diffie-Hellman public value (g^X mod p).\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 44] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
       struct {\r
           select (KeyExchangeAlgorithm) {\r
               case diffie_hellman:\r
                   ServerDHParams params;\r
                   Signature signed_params;\r
               case rsa:\r
                   ServerRSAParams params;\r
                   Signature signed_params;\r
           };\r
       } ServerKeyExchange;\r
\r
\r
       struct {                                                          |\r
           select (KeyExchangeAlgorithm) {                               |\r
               case diffie_hellman:                                      |\r
                   ServerDHParams params;                                |\r
               case rsa:                                                 |\r
                   ServerRSAParams params;                               |\r
           };                                                            |\r
        } ServerParams;                                                  |\r
\r
\r
       params\r
           The server's key exchange parameters.\r
\r
\r
       signed_params\r
           For non-anonymous key exchanges, a hash of the corresponding\r
           params value, with the signature appropriate to that hash\r
           applied.\r
\r
\r
       md5_hash\r
           MD5(ClientHello.random + ServerHello.random + ServerParams);\r
\r
\r
       sha_hash\r
           SHA(ClientHello.random + ServerHello.random + ServerParams);\r
\r
\r
       enum { anonymous, rsa, dsa } SignatureAlgorithm;\r
\r
\r
\r
       select (SignatureAlgorithm)                                       |\r
       {                                                                 |\r
           case anonymous: struct { };                                   |\r
           case rsa:\r
               digitally-signed struct {\r
                   opaque md5_hash[16];\r
                   opaque sha_hash[20];\r
               };\r
           case dsa:\r
               digitally-signed struct {\r
                   opaque sha_hash[20];\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 45] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
               };\r
       } Signature;\r
\r
\r
7.4.4. Certificate request\r
\r
\r
   When this message will be sent:\r
       A non-anonymous server can optionally request a certificate from\r
       the client, if appropriate for the selected cipher suite. This\r
       message, if sent, will immediately follow the Server Key Exchange\r
       message (if it is sent; otherwise, the Server Certificate\r
       message).\r
\r
\r
   Structure of this message:\r
       enum {\r
           rsa_sign(1), dss_sign(2), rsa_fixed_dh(3), dss_fixed_dh(4),\r
        rsa_ephemeral_dh_RESERVED(5), dss_ephemeral_dh_RESERVED(6),      |\r
        fortezza_dms_RESERVED(20),                                       |\r
           (255)\r
       } ClientCertificateType;\r
\r
\r
       opaque DistinguishedName<1..2^16-1>;\r
\r
\r
       struct {\r
           ClientCertificateType certificate_types<1..2^8-1>;\r
           DistinguishedName certificate_authorities<0..2^16-1>;         |\r
       } CertificateRequest;\r
\r
\r
       certificate_types\r
           This field is a list of the types of certificates requested,  |\r
           sorted in order of the server's preference.                   |\r
\r
\r
       certificate_authorities\r
           A list of the distinguished names of acceptable certificate\r
           authorities. These distinguished names may specify a desired\r
           distinguished name for a root CA or for a subordinate CA;\r
           thus, this message can be used both to describe known roots   |\r
           and a desired authorization space. If the                     |\r
           certificate_authorities list is empty then the client MAY     |\r
           send any certificate of the appropriate                       |\r
           ClientCertificateType, unless there is some external          |\r
           arrangement to the contrary.                                  |\r
\r
\r
\r
 Note: Values listed as RESERVED may not be used. They were used in      |\r
           SSLv3.\r
\r
\r
 Note: DistinguishedName is derived from [X509].\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 46] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
 Note: It is a fatal handshake_failure alert for an anonymous server to\r
       request client authentication.                                    |\r
\r
\r
7.4.5. Server hello done\r
\r
\r
   When this message will be sent:\r
       The server hello done message is sent by the server to indicate\r
       the end of the server hello and associated messages. After\r
       sending this message the server will wait for a client response.\r
\r
\r
   Meaning of this message:\r
       This message means that the server is done sending messages to\r
       support the key exchange, and the client can proceed with its\r
       phase of the key exchange.\r
\r
\r
       Upon receipt of the server hello done message the client SHOULD   |\r
       verify that the server provided a valid certificate if required\r
       and check that the server hello parameters are acceptable.\r
\r
\r
   Structure of this message:\r
       struct { } ServerHelloDone;\r
\r
\r
7.4.6. Client certificate\r
\r
\r
   When this message will be sent:\r
       This is the first message the client can send after receiving a\r
       server hello done message. This message is only sent if the\r
       server requests a certificate. If no suitable certificate is\r
       available, the client should send a certificate message           |\r
       containing no certificates: I.e. the certificate_list structure   |\r
       should have a length of zero. If client authentication is         |\r
       required by the server for the handshake to continue, it may\r
       respond with a fatal handshake failure alert. Client certificates\r
       are sent using the Certificate structure defined in Section\r
       7.4.2.\r
\r
\r
\r
 Note: When using a static Diffie-Hellman based key exchange method      |\r
       (DH_DSS or DH_RSA), if client authentication is requested, the\r
       Diffie-Hellman group and generator encoded in the client's\r
       certificate must match the server specified Diffie-Hellman\r
       parameters if the client's parameters are to be used for the key\r
       exchange.\r
\r
\r
7.4.7. Client key exchange message\r
\r
\r
   When this message will be sent:\r
       This message is always sent by the client. It will immediately\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 47] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
       follow the client certificate message, if it is sent. Otherwise\r
       it will be the first message sent by the client after it receives\r
       the server hello done message.\r
\r
\r
   Meaning of this message:\r
       With this message, the premaster secret is set, either though\r
       direct transmission of the RSA-encrypted secret, or by the\r
       transmission of Diffie-Hellman parameters which will allow each\r
       side to agree upon the same premaster secret. When the key\r
       exchange method is DH_RSA or DH_DSS, client certification has\r
       been requested, and the client was able to respond with a\r
       certificate which contained a Diffie-Hellman public key whose\r
       parameters (group and generator) matched those specified by the   |\r
       server in its certificate, this message MUST not contain any\r
       data.\r
\r
\r
   Structure of this message:\r
       The choice of messages depends on which key exchange method has\r
       been selected. See Section 7.4.3 for the KeyExchangeAlgorithm\r
       definition.\r
\r
\r
       struct {\r
           select (KeyExchangeAlgorithm) {\r
               case rsa: EncryptedPreMasterSecret;\r
               case diffie_hellman: ClientDiffieHellmanPublic;\r
           } exchange_keys;\r
       } ClientKeyExchange;\r
\r
\r
7.4.7.1. RSA encrypted premaster secret message\r
\r
\r
   Meaning of this message:\r
       If RSA is being used for key agreement and authentication, the\r
       client generates a 48-byte premaster secret, encrypts it using\r
       the public key from the server's certificate or the temporary RSA\r
       key provided in a server key exchange message, and sends the\r
       result in an encrypted premaster secret message. This structure\r
       is a variant of the client key exchange message, not a message in\r
       itself.\r
\r
\r
   Structure of this message:\r
       struct {\r
           ProtocolVersion client_version;\r
           opaque random[46];\r
       } PreMasterSecret;\r
\r
\r
       client_version\r
           The latest (newest) version supported by the client. This is\r
           used to detect version roll-back attacks. Upon receiving the  |\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 48] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
           premaster secret, the server SHOULD check that this value\r
           matches the value transmitted by the client in the client\r
           hello message.\r
\r
\r
       random\r
           46 securely-generated random bytes.\r
\r
\r
       struct {\r
           public-key-encrypted PreMasterSecret pre_master_secret;\r
       } EncryptedPreMasterSecret;\r
\r
\r
       pre_master_secret                                                 |\r
           This random value is generated by the client and is used to   |\r
           generate the master secret, as specified in Section 8.1.      |\r
\r
\r
 Note: An attack discovered by Daniel Bleichenbacher [BLEI] can be used\r
       to attack a TLS server which is using PKCS#1 encoded RSA. The\r
       attack takes advantage of the fact that by failing in different\r
       ways, a TLS server can be coerced into revealing whether a\r
       particular message, when decrypted, is properly PKCS#1 formatted\r
       or not.\r
\r
\r
       The best way to avoid vulnerability to this attack is to treat\r
       incorrectly formatted messages in a manner indistinguishable from\r
       correctly formatted RSA blocks. Thus, when it receives an\r
       incorrectly formatted RSA block, a server should generate a\r
       random 48-byte value and proceed using it as the premaster\r
       secret. Thus, the server will act identically whether the         |\r
       received RSA block is correctly encoded or not.                   |\r
\r
\r
 Implementation Note: public-key-encrypted data is represented as an     |\r
       opaque vector <0..2^16-1> (see S. 4.7). Thus the RSA-encrypted    |\r
       PreMaster Secret in a ClientKeyExchange is preceded by two length |\r
       bytes. These bytes are redundant in the case of RSA because the   |\r
       EncryptedPreMasterSecret is the only data in the                  |\r
       ClientKeyExchange and its length can therefore be unambiguously   |\r
       determined. The SSLv3 specification was not clear about the       |\r
       encoding of public-key-encrypted data and therefore many SSLv3    |\r
       implementations do not include the the length bytes, encoding the |\r
       RSA encrypted data directly in the ClientKeyExchange message.     |\r
\r
\r
       This specification requires correct encoding of the               |\r
       EncryptedPreMasterSecret complete with length bytes. The          |\r
       resulting PDU is incompatible with many SSLv3 implementations.    |\r
       Implementors upgrading from SSLv3 must modify their               |\r
       implementations to generate and accept the correct encoding.      |\r
       Implementors who wish to be compatible with both SSLv3 and TLS    |\r
       should make their implementation's behavior dependent on the      |\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 49] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
       protocol version.                                                 |\r
\r
\r
 Implementation Note: It is now known that remote timing-based attacks   |\r
       on SSL are possible, at least when the client and server are on   |\r
       the same LAN. Accordingly, implementations which use static RSA   |\r
       keys SHOULD use RSA blinding or some other anti-timing technique, |\r
       as described in [TIMING].\r
\r
\r
 Note: The version number in the PreMasterSecret is that offered by the  |\r
       client, NOT the version negotiated for the connection. This       |\r
       feature is designed to prevent rollback attacks. Unfortunately,   |\r
       many implementations use the negotiated version instead and       |\r
       therefore checking the version number may lead to failure to      |\r
       interoperate with such incorrect client implementations. Client   |\r
       implementations MUST and Server implementations MAY check the     |\r
       version number. In practice, since there are no significant known |\r
       security differences between TLS and SSLv3, rollback to SSLv3 is  |\r
       not believed to be a serious security risk.  Note that if servers |\r
       choose to to check the version number, they should randomize the  |\r
       PreMasterSecret in case of error, rather than generate an alert,  |\r
       in order to avoid variants on the Bleichenbacher attack. [KPR03]\r
\r
\r
7.4.7.2. Client Diffie-Hellman public value\r
\r
\r
   Meaning of this message:\r
       This structure conveys the client's Diffie-Hellman public value\r
       (Yc) if it was not already included in the client's certificate.\r
       The encoding used for Yc is determined by the enumerated\r
       PublicValueEncoding. This structure is a variant of the client\r
       key exchange message, not a message in itself.\r
\r
\r
   Structure of this message:\r
       enum { implicit, explicit } PublicValueEncoding;\r
\r
\r
       implicit\r
           If the client certificate already contains a suitable Diffie-\r
           Hellman key, then Yc is implicit and does not need to be sent\r
           again. In this case, the Client Key Exchange message will be\r
           sent, but will be empty.\r
\r
\r
       explicit\r
           Yc needs to be sent.\r
\r
\r
       struct {\r
           select (PublicValueEncoding) {\r
               case implicit: struct { };\r
               case explicit: opaque dh_Yc<1..2^16-1>;\r
           } dh_public;\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 50] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
       } ClientDiffieHellmanPublic;\r
\r
\r
       dh_Yc\r
           The client's Diffie-Hellman public value (Yc).\r
\r
\r
7.4.8. Certificate verify\r
\r
\r
   When this message will be sent:\r
       This message is used to provide explicit verification of a client\r
       certificate. This message is only sent following a client\r
       certificate that has signing capability (i.e. all certificates\r
       except those containing fixed Diffie-Hellman parameters). When\r
       sent, it will immediately follow the client key exchange message.\r
\r
\r
   Structure of this message:\r
       struct {\r
            Signature signature;\r
       } CertificateVerify;\r
\r
\r
       The Signature type is defined in 7.4.3.\r
\r
\r
       CertificateVerify.signature.md5_hash\r
           MD5(handshake_messages);\r
\r
\r
       CertificateVerify.signature.sha_hash                              |\r
           SHA(handshake_messages);\r
\r
\r
   Here handshake_messages refers to all handshake messages sent or\r
   received starting at client hello up to but not including this\r
   message, including the type and length fields of the handshake\r
   messages. This is the concatenation of all the Handshake structures\r
   as defined in 7.4 exchanged thus far.\r
\r
\r
7.4.9. Finished\r
\r
\r
   When this message will be sent:\r
       A finished message is always sent immediately after a change\r
       cipher spec message to verify that the key exchange and\r
       authentication processes were successful. It is essential that a\r
       change cipher spec message be received between the other\r
       handshake messages and the Finished message.\r
\r
\r
   Meaning of this message:\r
       The finished message is the first protected with the just-\r
       negotiated algorithms, keys, and secrets. Recipients of finished  |\r
       messages MUST verify that the contents are correct.  Once a side\r
       has sent its Finished message and received and validated the\r
       Finished message from its peer, it may begin to send and receive\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 51] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
       application data over the connection.\r
\r
\r
       struct {\r
           opaque verify_data[12];\r
       } Finished;\r
\r
\r
       verify_data\r
           PRF(master_secret, finished_label, MD5(handshake_messages) +\r
           SHA-1(handshake_messages)) [0..11];\r
\r
\r
       finished_label\r
           For Finished messages sent by the client, the string "client\r
           finished". For Finished messages sent by the server, the\r
           string "server finished".\r
\r
\r
       handshake_messages\r
           All of the data from all handshake messages up to but not\r
           including this message. This is only data visible at the\r
           handshake layer and does not include record layer headers.\r
           This is the concatenation of all the Handshake structures as\r
           defined in 7.4 exchanged thus far.\r
\r
\r
   It is a fatal error if a finished message is not preceded by a change\r
   cipher spec message at the appropriate point in the handshake.\r
\r
\r
   The value handshake_messages includes all handshake messages starting |\r
   at client hello up to, but not including, this finished message. This\r
   may be different from handshake_messages in Section 7.4.8 because it\r
   would include the certificate verify message (if sent). Also, the\r
   handshake_messages for the finished message sent by the client will\r
   be different from that for the finished message sent by the server,\r
   because the one which is sent second will include the prior one.\r
\r
\r
 Note: Change cipher spec messages, alerts and any other record types\r
       are not handshake messages and are not included in the hash\r
       computations. Also, Hello Request messages are omitted from\r
       handshake hashes.\r
\r
\r
8. Cryptographic computations\r
\r
\r
   In order to begin connection protection, the TLS Record Protocol\r
   requires specification of a suite of algorithms, a master secret, and\r
   the client and server random values. The authentication, encryption,\r
   and MAC algorithms are determined by the cipher_suite selected by the\r
   server and revealed in the server hello message. The compression\r
   algorithm is negotiated in the hello messages, and the random values\r
   are exchanged in the hello messages. All that remains is to calculate\r
   the master secret.\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 52] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
8.1. Computing the master secret\r
\r
\r
   For all key exchange methods, the same algorithm is used to convert\r
   the pre_master_secret into the master_secret. The pre_master_secret\r
   should be deleted from memory once the master_secret has been\r
   computed.\r
\r
\r
       master_secret = PRF(pre_master_secret, "master secret",\r
                           ClientHello.random + ServerHello.random)\r
       [0..47];\r
\r
\r
   The master secret is always exactly 48 bytes in length. The length of\r
   the premaster secret will vary depending on key exchange method.\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 53] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
8.1.1. RSA\r
\r
\r
   When RSA is used for server authentication and key exchange, a\r
   48-byte pre_master_secret is generated by the client, encrypted under\r
   the server's public key, and sent to the server. The server uses its\r
   private key to decrypt the pre_master_secret. Both parties then\r
   convert the pre_master_secret into the master_secret, as specified\r
   above.\r
\r
\r
   RSA digital signatures are performed using PKCS #1 [PKCS1] block type\r
   1. RSA public key encryption is performed using PKCS #1 block type 2.\r
\r
\r
8.1.2. Diffie-Hellman\r
\r
\r
   A conventional Diffie-Hellman computation is performed. The\r
   negotiated key (Z) is used as the pre_master_secret, and is converted\r
   into the master_secret, as specified above.  Leading 0 bytes of Z are |\r
   stripped before it is used as the pre_master_secret.\r
\r
\r
 Note: Diffie-Hellman parameters are specified by the server, and may\r
       be either ephemeral or contained within the server's certificate.\r
\r
\r
9. Mandatory Cipher Suites\r
\r
\r
   In the absence of an application profile standard specifying\r
   otherwise, a TLS compliant application MUST implement the cipher      |\r
   suite TLS_RSA_WITH_3DES_EDE_CBC_SHA.                                  |\r
\r
\r
   The 40-bit cipher suites are known to be susceptible to exhaustive    |\r
   search attack by commercial attackers. Implementations of this        |\r
   document SHOULD disable them by default if they are supported at all. |\r
   A future version of this document may remove them entirely.\r
\r
\r
10. Application data protocol\r
\r
\r
   Application data messages are carried by the Record Layer and are\r
   fragmented, compressed and encrypted based on the current connection\r
   state. The messages are treated as transparent data to the record\r
   layer.\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 54] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
A. Protocol constant values\r
\r
\r
   This section describes protocol types and constants.\r
\r
\r
A.1. Record layer\r
\r
\r
    struct {\r
        uint8 major, minor;\r
    } ProtocolVersion;\r
\r
\r
    ProtocolVersion version = { 3, 2 };     /* TLS v1.1 */               |\r
\r
\r
    enum {\r
        change_cipher_spec(20), alert(21), handshake(22),\r
        application_data(23), (255)\r
    } ContentType;\r
\r
\r
    struct {\r
        ContentType type;\r
        ProtocolVersion version;\r
        uint16 length;\r
        opaque fragment[TLSPlaintext.length];\r
    } TLSPlaintext;\r
\r
\r
    struct {\r
        ContentType type;\r
        ProtocolVersion version;\r
        uint16 length;\r
        opaque fragment[TLSCompressed.length];\r
    } TLSCompressed;\r
\r
\r
    struct {\r
        ContentType type;\r
        ProtocolVersion version;\r
        uint16 length;\r
        select (CipherSpec.cipher_type) {\r
            case stream: GenericStreamCipher;\r
            case block:  GenericBlockCipher;\r
        } fragment;\r
    } TLSCiphertext;\r
\r
\r
    stream-ciphered struct {\r
        opaque content[TLSCompressed.length];\r
        opaque MAC[CipherSpec.hash_size];\r
    } GenericStreamCipher;\r
\r
\r
    block-ciphered struct {\r
        opaque IV[CipherSpec.block_length];                              |\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 55] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
        opaque content[TLSCompressed.length];\r
        opaque MAC[CipherSpec.hash_size];\r
        uint8 padding[GenericBlockCipher.padding_length];\r
        uint8 padding_length;\r
    } GenericBlockCipher;\r
\r
\r
A.2. Change cipher specs message\r
\r
\r
    struct {\r
        enum { change_cipher_spec(1), (255) } type;\r
    } ChangeCipherSpec;\r
\r
\r
A.3. Alert messages\r
\r
\r
    enum { warning(1), fatal(2), (255) } AlertLevel;\r
\r
\r
        enum {\r
            close_notify(0),\r
            unexpected_message(10),\r
            bad_record_mac(20),\r
            decryption_failed(21),\r
            record_overflow(22),\r
            decompression_failure(30),\r
            handshake_failure(40),\r
         no_certificate_RESERVED (41),                                   |\r
            bad_certificate(42),\r
            unsupported_certificate(43),\r
            certificate_revoked(44),\r
            certificate_expired(45),\r
            certificate_unknown(46),\r
            illegal_parameter(47),\r
            unknown_ca(48),\r
            access_denied(49),\r
            decode_error(50),\r
            decrypt_error(51),\r
            export_restriction(60),\r
            protocol_version(70),\r
            insufficient_security(71),\r
            internal_error(80),\r
            user_canceled(90),\r
            no_renegotiation(100),\r
            (255)\r
        } AlertDescription;\r
\r
\r
    struct {\r
        AlertLevel level;\r
        AlertDescription description;\r
    } Alert;\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 56] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
A.4. Handshake protocol\r
\r
\r
    enum {\r
        hello_request(0), client_hello(1), server_hello(2),\r
        certificate(11), server_key_exchange (12),\r
        certificate_request(13), server_hello_done(14),\r
        certificate_verify(15), client_key_exchange(16),\r
        finished(20), (255)\r
    } HandshakeType;\r
\r
\r
    struct {\r
        HandshakeType msg_type;\r
        uint24 length;\r
        select (HandshakeType) {\r
            case hello_request:       HelloRequest;\r
            case client_hello:        ClientHello;\r
            case server_hello:        ServerHello;\r
            case certificate:         Certificate;\r
            case server_key_exchange: ServerKeyExchange;\r
            case certificate_request: CertificateRequest;\r
            case server_hello_done:   ServerHelloDone;\r
            case certificate_verify:  CertificateVerify;\r
            case client_key_exchange: ClientKeyExchange;\r
            case finished:            Finished;\r
        } body;\r
    } Handshake;\r
\r
\r
A.4.1. Hello messages\r
\r
\r
    struct { } HelloRequest;\r
\r
\r
    struct {\r
        uint32 gmt_unix_time;\r
        opaque random_bytes[28];\r
    } Random;\r
\r
\r
    opaque SessionID<0..32>;\r
\r
\r
    uint8 CipherSuite[2];\r
\r
\r
    enum { null(0), (255) } CompressionMethod;\r
\r
\r
    struct {\r
        ProtocolVersion client_version;\r
        Random random;\r
        SessionID session_id;\r
        CipherSuite cipher_suites<2..2^16-1>;\r
        CompressionMethod compression_methods<1..2^8-1>;\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 57] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
    } ClientHello;\r
\r
\r
    struct {\r
        ProtocolVersion server_version;\r
        Random random;\r
        SessionID session_id;\r
        CipherSuite cipher_suite;\r
        CompressionMethod compression_method;\r
    } ServerHello;\r
\r
\r
A.4.2. Server authentication and key exchange messages\r
\r
\r
    opaque ASN.1Cert<2^24-1>;\r
\r
\r
    struct {\r
        ASN.1Cert certificate_list<0..2^24-1>;                           |\r
    } Certificate;\r
\r
\r
    enum { rsa, diffie_hellman } KeyExchangeAlgorithm;\r
\r
\r
    struct {\r
        opaque RSA_modulus<1..2^16-1>;\r
        opaque RSA_exponent<1..2^16-1>;\r
    } ServerRSAParams;\r
\r
\r
    struct {\r
        opaque DH_p<1..2^16-1>;\r
        opaque DH_g<1..2^16-1>;\r
        opaque DH_Ys<1..2^16-1>;\r
    } ServerDHParams;\r
\r
\r
    struct {\r
        select (KeyExchangeAlgorithm) {\r
            case diffie_hellman:\r
                ServerDHParams params;\r
                Signature signed_params;\r
            case rsa:\r
                ServerRSAParams params;\r
                Signature signed_params;\r
        };\r
    } ServerKeyExchange;\r
\r
\r
    enum { anonymous, rsa, dsa } SignatureAlgorithm;                     |\r
\r
\r
    struct {                                                             |\r
        select (KeyExchangeAlgorithm) {                                  |\r
            case diffie_hellman:                                         |\r
                ServerDHParams params;                                   |\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 58] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
            case rsa:                                                    |\r
                ServerRSAParams params;                                  |\r
        };                                                               |\r
     } ServerParams;                                                     |\r
\r
\r
    select (SignatureAlgorithm)\r
    {   case anonymous: struct { };\r
        case rsa:\r
            digitally-signed struct {\r
                opaque md5_hash[16];\r
                opaque sha_hash[20];\r
            };\r
        case dsa:\r
            digitally-signed struct {\r
                opaque sha_hash[20];\r
            };\r
    } Signature;\r
\r
\r
    enum {\r
        rsa_sign(1), dss_sign(2), rsa_fixed_dh(3), dss_fixed_dh(4),\r
     rsa_ephemeral_dh_RESERVED(5), dss_ephemeral_dh_RESERVED(6),         |\r
     fortezza_dms_RESERVED(20),                                          |\r
     (255)                                                               |\r
    } ClientCertificateType;\r
\r
\r
    opaque DistinguishedName<1..2^16-1>;\r
\r
\r
    struct {\r
        ClientCertificateType certificate_types<1..2^8-1>;\r
        DistinguishedName certificate_authorities<0..2^16-1>;            |\r
    } CertificateRequest;\r
\r
\r
    struct { } ServerHelloDone;\r
\r
\r
A.4.3. Client authentication and key exchange messages\r
\r
\r
    struct {\r
        select (KeyExchangeAlgorithm) {\r
            case rsa: EncryptedPreMasterSecret;\r
            case diffie_hellman: DiffieHellmanClientPublicValue;\r
        } exchange_keys;\r
    } ClientKeyExchange;\r
\r
\r
    struct {\r
        ProtocolVersion client_version;\r
        opaque random[46];\r
    } PreMasterSecret;\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 59] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
    struct {\r
        public-key-encrypted PreMasterSecret pre_master_secret;\r
    } EncryptedPreMasterSecret;\r
\r
\r
    enum { implicit, explicit } PublicValueEncoding;\r
\r
\r
    struct {\r
        select (PublicValueEncoding) {\r
            case implicit: struct {};\r
            case explicit: opaque DH_Yc<1..2^16-1>;\r
        } dh_public;\r
    } ClientDiffieHellmanPublic;\r
\r
\r
    struct {\r
        Signature signature;\r
    } CertificateVerify;\r
\r
\r
A.4.4. Handshake finalization message\r
\r
\r
    struct {\r
        opaque verify_data[12];\r
    } Finished;\r
\r
\r
A.5. The CipherSuite\r
\r
\r
   The following values define the CipherSuite codes used in the client\r
   hello and server hello messages.\r
\r
\r
   A CipherSuite defines a cipher specification supported in TLS Version |\r
   1.1.\r
\r
\r
   TLS_NULL_WITH_NULL_NULL is specified and is the initial state of a\r
   TLS connection during the first handshake on that channel, but must\r
   not be negotiated, as it provides no more protection than an\r
   unsecured connection.\r
\r
\r
    CipherSuite TLS_NULL_WITH_NULL_NULL                = { 0x00,0x00 };\r
\r
\r
   The following CipherSuite definitions require that the server provide\r
   an RSA certificate that can be used for key exchange. The server may\r
   request either an RSA or a DSS signature-capable certificate in the\r
   certificate request message.\r
\r
\r
    CipherSuite TLS_RSA_WITH_NULL_MD5                  = { 0x00,0x01 };\r
    CipherSuite TLS_RSA_WITH_NULL_SHA                  = { 0x00,0x02 };\r
    CipherSuite TLS_RSA_EXPORT_WITH_RC4_40_MD5         = { 0x00,0x03 };\r
    CipherSuite TLS_RSA_WITH_RC4_128_MD5               = { 0x00,0x04 };\r
    CipherSuite TLS_RSA_WITH_RC4_128_SHA               = { 0x00,0x05 };\r
\r
\r
\r
\r
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\r
\r
\r
    CipherSuite TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5     = { 0x00,0x06 };\r
    CipherSuite TLS_RSA_WITH_IDEA_CBC_SHA              = { 0x00,0x07 };\r
    CipherSuite TLS_RSA_EXPORT_WITH_DES40_CBC_SHA      = { 0x00,0x08 };\r
    CipherSuite TLS_RSA_WITH_DES_CBC_SHA               = { 0x00,0x09 };\r
    CipherSuite TLS_RSA_WITH_3DES_EDE_CBC_SHA          = { 0x00,0x0A };\r
\r
\r
   The following CipherSuite definitions are used for server-\r
   authenticated (and optionally client-authenticated) Diffie-Hellman.\r
   DH denotes cipher suites in which the server's certificate contains\r
   the Diffie-Hellman parameters signed by the certificate authority\r
   (CA). DHE denotes ephemeral Diffie-Hellman, where the Diffie-Hellman\r
   parameters are signed by a DSS or RSA certificate, which has been\r
   signed by the CA. The signing algorithm used is specified after the\r
   DH or DHE parameter. The server can request an RSA or DSS signature-\r
   capable certificate from the client for client authentication or it\r
   may request a Diffie-Hellman certificate. Any Diffie-Hellman\r
   certificate provided by the client must use the parameters (group and\r
   generator) described by the server.\r
\r
\r
    CipherSuite TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA   = { 0x00,0x0B };\r
    CipherSuite TLS_DH_DSS_WITH_DES_CBC_SHA            = { 0x00,0x0C };\r
    CipherSuite TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA       = { 0x00,0x0D };\r
    CipherSuite TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA   = { 0x00,0x0E };\r
    CipherSuite TLS_DH_RSA_WITH_DES_CBC_SHA            = { 0x00,0x0F };\r
    CipherSuite TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA       = { 0x00,0x10 };\r
    CipherSuite TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA  = { 0x00,0x11 };\r
    CipherSuite TLS_DHE_DSS_WITH_DES_CBC_SHA           = { 0x00,0x12 };\r
    CipherSuite TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA      = { 0x00,0x13 };\r
    CipherSuite TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA  = { 0x00,0x14 };\r
    CipherSuite TLS_DHE_RSA_WITH_DES_CBC_SHA           = { 0x00,0x15 };\r
    CipherSuite TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA      = { 0x00,0x16 };\r
\r
\r
   The following cipher suites are used for completely anonymous Diffie-\r
   Hellman communications in which neither party is authenticated. Note\r
   that this mode is vulnerable to man-in-the-middle attacks and is\r
   therefore deprecated.\r
\r
\r
    CipherSuite TLS_DH_anon_EXPORT_WITH_RC4_40_MD5     = { 0x00,0x17 };\r
    CipherSuite TLS_DH_anon_WITH_RC4_128_MD5           = { 0x00,0x18 };\r
    CipherSuite TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA  = { 0x00,0x19 };\r
    CipherSuite TLS_DH_anon_WITH_DES_CBC_SHA           = { 0x00,0x1A };\r
    CipherSuite TLS_DH_anon_WITH_3DES_EDE_CBC_SHA      = { 0x00,0x1B };\r
\r
\r
 Note: All cipher suites whose first byte is 0xFF are considered\r
       private and can be used for defining local/experimental\r
       algorithms. Interoperability of such types is a local matter.\r
\r
\r
 Note: Additional cipher suites can be registered by publishing an RFC\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 61] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
       which specifies the cipher suites, including the necessary TLS\r
       protocol information, including message encoding, premaster\r
       secret derivation, symmetric encryption and MAC calculation and\r
       appropriate reference information for the algorithms involved.\r
       The RFC editor's office may, at its discretion, choose to publish\r
       specifications for cipher suites which are not completely\r
       described (e.g., for classified algorithms) if it finds the\r
       specification to be of technical interest and completely\r
       specified.\r
\r
\r
 Note: The cipher suite values { 0x00, 0x1C } and { 0x00, 0x1D } are\r
       reserved to avoid collision with Fortezza-based cipher suites in\r
       SSL 3.\r
\r
\r
A.6. The Security Parameters\r
\r
\r
   These security parameters are determined by the TLS Handshake\r
   Protocol and provided as parameters to the TLS Record Layer in order\r
   to initialize a connection state. SecurityParameters includes:\r
\r
\r
       enum { null(0), (255) } CompressionMethod;\r
\r
\r
       enum { server, client } ConnectionEnd;\r
\r
\r
       enum { null, rc4, rc2, des, 3des, des40, idea }\r
       BulkCipherAlgorithm;\r
\r
\r
       enum { stream, block } CipherType;\r
\r
\r
       enum { true, false } IsExportable;\r
\r
\r
       enum { null, md5, sha } MACAlgorithm;\r
\r
\r
   /* The algorithms specified in CompressionMethod,\r
   BulkCipherAlgorithm, and MACAlgorithm may be added to. */\r
\r
\r
       struct {\r
           ConnectionEnd entity;\r
           BulkCipherAlgorithm bulk_cipher_algorithm;\r
           CipherType cipher_type;\r
           uint8 key_size;\r
           uint8 key_material_length;\r
           IsExportable is_exportable;\r
           MACAlgorithm mac_algorithm;\r
           uint8 hash_size;\r
           CompressionMethod compression_algorithm;\r
           opaque master_secret[48];\r
           opaque client_random[32];\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 62] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
           opaque server_random[32];\r
       } SecurityParameters;\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 63] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
B. Glossary\r
\r
\r
   application protocol\r
       An application protocol is a protocol that normally layers\r
       directly on top of the transport layer (e.g., TCP/IP). Examples\r
       include HTTP, TELNET, FTP, and SMTP.\r
\r
\r
   asymmetric cipher\r
       See public key cryptography.\r
\r
\r
   authentication\r
       Authentication is the ability of one entity to determine the\r
       identity of another entity.\r
\r
\r
   block cipher\r
       A block cipher is an algorithm that operates on plaintext in\r
       groups of bits, called blocks. 64 bits is a common block size.\r
\r
\r
   bulk cipher\r
       A symmetric encryption algorithm used to encrypt large quantities\r
       of data.\r
\r
\r
   cipher block chaining (CBC)\r
       CBC is a mode in which every plaintext block encrypted with a\r
       block cipher is first exclusive-ORed with the previous ciphertext\r
       block (or, in the case of the first block, with the\r
       initialization vector). For decryption, every block is first\r
       decrypted, then exclusive-ORed with the previous ciphertext block\r
       (or IV).\r
\r
\r
   certificate\r
       As part of the X.509 protocol (a.k.a. ISO Authentication\r
       framework), certificates are assigned by a trusted Certificate\r
       Authority and provide a strong binding between a party's identity\r
       or some other attributes and its public key.\r
\r
\r
   client\r
       The application entity that initiates a TLS connection to a\r
       server. This may or may not imply that the client initiated the\r
       underlying transport connection. The primary operational\r
       difference between the server and client is that the server is\r
       generally authenticated, while the client is only optionally\r
       authenticated.\r
\r
\r
   client write key\r
       The key used to encrypt data written by the client.\r
\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 64] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   client write MAC secret\r
       The secret data used to authenticate data written by the client.\r
\r
\r
   connection\r
       A connection is a transport (in the OSI layering model\r
       definition) that provides a suitable type of service. For TLS,\r
       such connections are peer to peer relationships. The connections\r
       are transient. Every connection is associated with one session.\r
\r
\r
   Data Encryption Standard\r
       DES is a very widely used symmetric encryption algorithm. DES is\r
       a block cipher with a 56 bit key and an 8 byte block size. Note\r
       that in TLS, for key generation purposes, DES is treated as\r
       having an 8 byte key length (64 bits), but it still only provides\r
       56 bits of protection. (The low bit of each key byte is presumed\r
       to be set to produce odd parity in that key byte.) DES can also\r
       be operated in a mode where three independent keys and three\r
       encryptions are used for each block of data; this uses 168 bits\r
       of key (24 bytes in the TLS key generation method) and provides\r
       the equivalent of 112 bits of security. [DES], [3DES]\r
\r
\r
   Digital Signature Standard (DSS)\r
       A standard for digital signing, including the Digital Signing\r
       Algorithm, approved by the National Institute of Standards and\r
       Technology, defined in NIST FIPS PUB 186, "Digital Signature\r
       Standard," published May, 1994 by the U.S. Dept. of Commerce.\r
       [DSS]\r
\r
\r
   digital signatures                                                    |\r
       Digital signatures utilize public key cryptography and one-way\r
       hash functions to produce a signature of the data that can be\r
       authenticated, and is difficult to forge or repudiate.\r
\r
\r
   handshake\r
       An initial negotiation between client and server that establishes\r
       the parameters of their transactions.\r
\r
\r
   Initialization Vector (IV)\r
       When a block cipher is used in CBC mode, the initialization\r
       vector is exclusive-ORed with the first plaintext block prior to\r
       encryption.\r
\r
\r
   IDEA\r
       A 64-bit block cipher designed by Xuejia Lai and James Massey.\r
       [IDEA]\r
\r
\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 65] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   Message Authentication Code (MAC)\r
       A Message Authentication Code is a one-way hash computed from a\r
       message and some secret data. It is difficult to forge without\r
       knowing the secret data. Its purpose is to detect if the message\r
       has been altered.\r
\r
\r
   master secret\r
       Secure secret data used for generating encryption keys, MAC\r
       secrets, and IVs.\r
\r
\r
   MD5\r
       MD5 is a secure hashing function that converts an arbitrarily\r
       long data stream into a digest of fixed size (16 bytes). [MD5]\r
\r
\r
   public key cryptography\r
       A class of cryptographic techniques employing two-key ciphers.\r
       Messages encrypted with the public key can only be decrypted with\r
       the associated private key. Conversely, messages signed with the\r
       private key can be verified with the public key.\r
\r
\r
   one-way hash function\r
       A one-way transformation that converts an arbitrary amount of\r
       data into a fixed-length hash. It is computationally hard to\r
       reverse the transformation or to find collisions. MD5 and SHA are\r
       examples of one-way hash functions.\r
\r
\r
   RC2\r
       A block cipher developed by Ron Rivest at RSA Data Security, Inc.\r
       [RSADSI] described in [RC2].\r
\r
\r
   RC4\r
       A stream cipher licensed by RSA Data Security [RSADSI]. A\r
       compatible cipher is described in [RC4].\r
\r
\r
   RSA\r
       A very widely used public-key algorithm that can be used for\r
       either encryption or digital signing. [RSA]\r
\r
\r
   salt\r
       Non-secret random data used to make export encryption keys resist\r
       precomputation attacks.\r
\r
\r
   server\r
       The server is the application entity that responds to requests\r
       for connections from clients. See also under client.\r
\r
\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 66] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
   session\r
       A TLS session is an association between a client and a server.\r
       Sessions are created by the handshake protocol. Sessions define a\r
       set of cryptographic security parameters, which can be shared\r
       among multiple connections. Sessions are used to avoid the\r
       expensive negotiation of new security parameters for each\r
       connection.\r
\r
\r
   session identifier\r
       A session identifier is a value generated by a server that\r
       identifies a particular session.\r
\r
\r
   server write key\r
       The key used to encrypt data written by the server.\r
\r
\r
   server write MAC secret\r
       The secret data used to authenticate data written by the server.\r
\r
\r
   SHA\r
       The Secure Hash Algorithm is defined in FIPS PUB 180-1. It\r
       produces a 20-byte output. Note that all references to SHA\r
       actually use the modified SHA-1 algorithm. [SHA]\r
\r
\r
   SSL\r
       Netscape's Secure Socket Layer protocol [SSL3]. TLS is based on\r
       SSL Version 3.0\r
\r
\r
   stream cipher\r
       An encryption algorithm that converts a key into a\r
       cryptographically-strong keystream, which is then exclusive-ORed\r
       with the plaintext.\r
\r
\r
   symmetric cipher                                                      |\r
       See bulk cipher.\r
\r
\r
   Transport Layer Security (TLS)\r
       This protocol; also, the Transport Layer Security working group\r
       of the Internet Engineering Task Force (IETF). See "Comments" at\r
       the end of this document.\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 67] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
C. CipherSuite definitions\r
\r
\r
CipherSuite                      Is       Key          Cipher      Hash\r
                             Exportable Exchange\r
\r
\r
TLS_NULL_WITH_NULL_NULL               * NULL           NULL        NULL\r
TLS_RSA_WITH_NULL_MD5                 * RSA            NULL         MD5\r
TLS_RSA_WITH_NULL_SHA                 * RSA            NULL         SHA\r
TLS_RSA_EXPORT_WITH_RC4_40_MD5        * RSA_EXPORT     RC4_40       MD5\r
TLS_RSA_WITH_RC4_128_MD5                RSA            RC4_128      MD5\r
TLS_RSA_WITH_RC4_128_SHA                RSA            RC4_128      SHA\r
TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5    * RSA_EXPORT     RC2_CBC_40   MD5\r
TLS_RSA_WITH_IDEA_CBC_SHA               RSA            IDEA_CBC     SHA\r
TLS_RSA_EXPORT_WITH_DES40_CBC_SHA     * RSA_EXPORT     DES40_CBC    SHA\r
TLS_RSA_WITH_DES_CBC_SHA                RSA            DES_CBC      SHA\r
TLS_RSA_WITH_3DES_EDE_CBC_SHA           RSA            3DES_EDE_CBC SHA\r
TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA  * DH_DSS_EXPORT  DES40_CBC    SHA\r
TLS_DH_DSS_WITH_DES_CBC_SHA             DH_DSS         DES_CBC      SHA\r
TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA        DH_DSS         3DES_EDE_CBC SHA\r
TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA  * DH_RSA_EXPORT  DES40_CBC    SHA\r
TLS_DH_RSA_WITH_DES_CBC_SHA             DH_RSA         DES_CBC      SHA\r
TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA        DH_RSA         3DES_EDE_CBC SHA\r
TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA * DHE_DSS_EXPORT DES40_CBC    SHA\r
TLS_DHE_DSS_WITH_DES_CBC_SHA            DHE_DSS        DES_CBC      SHA\r
TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA       DHE_DSS        3DES_EDE_CBC SHA\r
TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA * DHE_RSA_EXPORT DES40_CBC    SHA\r
TLS_DHE_RSA_WITH_DES_CBC_SHA            DHE_RSA        DES_CBC      SHA\r
TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA       DHE_RSA        3DES_EDE_CBC SHA\r
TLS_DH_anon_EXPORT_WITH_RC4_40_MD5    * DH_anon_EXPORT RC4_40       MD5\r
TLS_DH_anon_WITH_RC4_128_MD5            DH_anon        RC4_128      MD5\r
TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA   DH_anon        DES40_CBC    SHA\r
TLS_DH_anon_WITH_DES_CBC_SHA            DH_anon        DES_CBC      SHA\r
TLS_DH_anon_WITH_3DES_EDE_CBC_SHA       DH_anon        3DES_EDE_CBC SHA\r
\r
\r
\r
   * Indicates IsExportable is True\r
\r
\r
      Key\r
      Exchange\r
      Algorithm       Description                        Key size limit\r
\r
\r
      DHE_DSS         Ephemeral DH with DSS signatures   None\r
      DHE_DSS_EXPORT  Ephemeral DH with DSS signatures   DH = 512 bits\r
      DHE_RSA         Ephemeral DH with RSA signatures   None\r
      DHE_RSA_EXPORT  Ephemeral DH with RSA signatures   DH = 512 bits,\r
                                                         RSA = none\r
      DH_anon         Anonymous DH, no signatures        None\r
      DH_anon_EXPORT  Anonymous DH, no signatures        DH = 512 bits\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 68] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
\r
\r
\r
      DH_DSS          DH with DSS-based certificates     None\r
      DH_DSS_EXPORT   DH with DSS-based certificates     DH = 512 bits\r
      DH_RSA          DH with RSA-based certificates     None\r
      DH_RSA_EXPORT   DH with RSA-based certificates     DH = 512 bits,\r
                                                         RSA = none\r
      NULL            No key exchange                    N/A\r
      RSA             RSA key exchange                   None\r
      RSA_EXPORT      RSA key exchange                   RSA = 512 bits\r
\r
\r
   Key size limit\r
       The key size limit gives the size of the largest public key that\r
       can be legally used for encryption or key agreement in            |\r
       cipher suites that are exportable.                                |\r
\r
\r
                         Key      Expanded   Effective   IV    Block\r
    Cipher       Type  Material Key Material  Key Bits  Size   Size\r
\r
\r
    NULL       * Stream   0          0           0        0     N/A\r
    IDEA_CBC     Block   16         16         128        8      8\r
    RC2_CBC_40 * Block    5         16          40        8      8\r
    RC4_40     * Stream   5         16          40        0     N/A\r
    RC4_128      Stream  16         16         128        0     N/A\r
    DES40_CBC  * Block    5          8          40        8      8\r
    DES_CBC      Block    8          8          56        8      8\r
    3DES_EDE_CBC Block   24         24         168        8      8\r
\r
\r
   * Indicates IsExportable is true.\r
\r
\r
   Type\r
       Indicates whether this is a stream cipher or a block cipher\r
       running in CBC mode.\r
\r
\r
   Key Material\r
       The number of bytes from the key_block that are used for\r
       generating the write keys.\r
\r
\r
   Expanded Key Material\r
       The number of bytes actually fed into the encryption algorithm\r
\r
\r
   Effective Key Bits\r
       How much entropy material is in the key material being fed into\r
       the encryption routines.\r
\r
\r
   IV Size\r
       How much data needs to be generated for the initialization\r
       vector. Zero for stream ciphers; equal to the block size for\r
       block ciphers.\r
\r
\r
\r
\r
\r
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\r
\r
\r
   Block Size\r
       The amount of data a block cipher enciphers in one chunk; a\r
       block cipher running in CBC mode can only encrypt an even\r
       multiple of its block size.\r
\r
\r
      Hash      Hash      Padding\r
    function    Size       Size\r
      NULL       0          0\r
      MD5        16         48\r
      SHA        20         40\r
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Dierks & Rescorla            Standards Track                    [Page 70] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
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\r
D. Implementation Notes\r
\r
\r
   The TLS protocol cannot prevent many common security mistakes. This\r
   section provides several recommendations to assist implementors.\r
\r
\r
D.1. Temporary RSA keys\r
\r
\r
   US Export restrictions limit RSA keys used for encryption to 512\r
   bits, but do not place any limit on lengths of RSA keys used for\r
   signing operations. Certificates often need to be larger than 512\r
   bits, since 512-bit RSA keys are not secure enough for high-value\r
   transactions or for applications requiring long-term security. Some\r
   certificates are also designated signing-only, in which case they\r
   cannot be used for key exchange.\r
\r
\r
   When the public key in the certificate cannot be used for encryption,\r
   the server signs a temporary RSA key, which is then exchanged. In\r
   exportable applications, the temporary RSA key should be the maximum\r
   allowable length (i.e., 512 bits). Because 512-bit RSA keys are\r
   relatively insecure, they should be changed often. For typical\r
   electronic commerce applications, it is suggested that keys be\r
   changed daily or every 500 transactions, and more often if possible.\r
   Note that while it is acceptable to use the same temporary key for\r
   multiple transactions, it must be signed each time it is used.\r
\r
\r
   RSA key generation is a time-consuming process. In many cases, a low-\r
   priority process can be assigned the task of key generation.\r
\r
\r
   Whenever a new key is completed, the existing temporary key can be\r
   replaced with the new one.\r
\r
\r
D.2. Random Number Generation and Seeding\r
\r
\r
   TLS requires a cryptographically-secure pseudorandom number generator\r
   (PRNG). Care must be taken in designing and seeding PRNGs.  PRNGs\r
   based on secure hash operations, most notably MD5 and/or SHA, are\r
   acceptable, but cannot provide more security than the size of the\r
   random number generator state. (For example, MD5-based PRNGs usually\r
   provide 128 bits of state.)\r
\r
\r
   To estimate the amount of seed material being produced, add the\r
   number of bits of unpredictable information in each seed byte. For\r
   example, keystroke timing values taken from a PC compatible's 18.2 Hz\r
   timer provide 1 or 2 secure bits each, even though the total size of\r
   the counter value is 16 bits or more. To seed a 128-bit PRNG, one\r
   would thus require approximately 100 such timer values.\r
\r
\r
D.3. Certificates and authentication\r
\r
\r
\r
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Dierks & Rescorla            Standards Track                    [Page 71] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
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\r
   Implementations are responsible for verifying the integrity of\r
   certificates and should generally support certificate revocation\r
   messages. Certificates should always be verified to ensure proper\r
   signing by a trusted Certificate Authority (CA). The selection and\r
   addition of trusted CAs should be done very carefully. Users should\r
   be able to view information about the certificate and root CA.\r
\r
\r
D.4. CipherSuites\r
\r
\r
   TLS supports a range of key sizes and security levels, including some\r
   which provide no or minimal security. A proper implementation will\r
   probably not support many cipher suites. For example, 40-bit\r
   encryption is easily broken, so implementations requiring strong\r
   security should not allow 40-bit keys. Similarly, anonymous Diffie-\r
   Hellman is strongly discouraged because it cannot prevent man-in-the-\r
   middle attacks. Applications should also enforce minimum and maximum\r
   key sizes. For example, certificate chains containing 512-bit RSA\r
   keys or signatures are not appropriate for high-security\r
   applications.\r
\r
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Dierks & Rescorla            Standards Track                    [Page 72] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
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\r
E. Backward Compatibility With SSL\r
\r
\r
   For historical reasons and in order to avoid a profligate consumption\r
   of reserved port numbers, application protocols which are secured by  |\r
   TLS 1.1, TLS 1.0, SSL 3.0, and SSL 2.0 all frequently share the same\r
   connection port: for example, the https protocol (HTTP secured by SSL\r
   or TLS) uses port 443 regardless of which security protocol it is\r
   using. Thus, some mechanism must be determined to distinguish and\r
   negotiate among the various protocols.\r
\r
\r
   TLS versions 1.1, 1.0, and SSL 3.0 are very similar; thus, supporting |\r
   both is easy. TLS clients who wish to negotiate with such older       |\r
   servers SHOULD send client hello messages using the SSL 3.0 record    |\r
   format and client hello structure, sending {3, 2} for the version     |\r
   field to note that they support TLS 1.1. If the server supports only  |\r
   TLS 1.0 or SSL 3.0, it will respond with a downrev 3.0 server hello;  |\r
   if it supports TLS 1.1 it will respond with a TLS 1.1 server hello.   |\r
   The negotiation then proceeds as appropriate for the negotiated\r
   protocol.\r
\r
\r
   Similarly, a TLS 1.1  server which wishes to interoperate with TLS    |\r
   1.0 or SSL 3.0 clients SHOULD accept SSL 3.0 client hello messages    |\r
   and respond with a SSL 3.0 server hello if an SSL 3.0 client hello    |\r
   with a version field of {3, 0} is received, denoting that this client |\r
   does not support TLS. Similarly, if a SSL 3.0 or TLS 1.0 hello with a |\r
   version field of {3, 1} is received, the server SHOULD respond with a |\r
   TLS 1.0 hello with a version field of {3, 1}.\r
\r
\r
   Whenever a client already knows the highest protocol known to a       |\r
   server (for example, when resuming a session), it SHOULD initiate the\r
   connection in that native protocol.\r
\r
\r
   TLS 1.1 clients that support SSL Version 2.0 servers MUST send SSL    |\r
   Version 2.0 client hello messages [SSL2]. TLS servers SHOULD accept\r
   either client hello format if they wish to support SSL 2.0 clients on\r
   the same connection port. The only deviations from the Version 2.0\r
   specification are the ability to specify a version with a value of\r
   three and the support for more ciphering types in the CipherSpec.\r
\r
\r
 Warning: The ability to send Version 2.0 client hello messages will be\r
          phased out with all due haste. Implementors SHOULD make every  |\r
          effort to move forward as quickly as possible. Version 3.0\r
          provides better mechanisms for moving to newer versions.\r
\r
\r
   The following cipher specifications are carryovers from SSL Version\r
   2.0. These are assumed to use RSA for key exchange and\r
   authentication.\r
\r
\r
\r
\r
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Dierks & Rescorla            Standards Track                    [Page 73] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
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\r
       V2CipherSpec TLS_RC4_128_WITH_MD5          = { 0x01,0x00,0x80 };\r
       V2CipherSpec TLS_RC4_128_EXPORT40_WITH_MD5 = { 0x02,0x00,0x80 };\r
       V2CipherSpec TLS_RC2_CBC_128_CBC_WITH_MD5  = { 0x03,0x00,0x80 };\r
       V2CipherSpec TLS_RC2_CBC_128_CBC_EXPORT40_WITH_MD5\r
                                                  = { 0x04,0x00,0x80 };\r
       V2CipherSpec TLS_IDEA_128_CBC_WITH_MD5     = { 0x05,0x00,0x80 };\r
       V2CipherSpec TLS_DES_64_CBC_WITH_MD5       = { 0x06,0x00,0x40 };\r
       V2CipherSpec TLS_DES_192_EDE3_CBC_WITH_MD5 = { 0x07,0x00,0xC0 };\r
\r
\r
   Cipher specifications native to TLS can be included in Version 2.0\r
   client hello messages using the syntax below. Any V2CipherSpec\r
   element with its first byte equal to zero will be ignored by Version  |\r
   2.0 servers. Clients sending any of the above V2CipherSpecs SHOULD\r
   also include the TLS equivalent (see Appendix A.5):\r
\r
\r
       V2CipherSpec (see TLS name) = { 0x00, CipherSuite };\r
\r
\r
E.1. Version 2 client hello\r
\r
\r
   The Version 2.0 client hello message is presented below using this\r
   document's presentation model. The true definition is still assumed   |\r
   to be the SSL Version 2.0 specification. Note that this message MUST  |\r
   be sent directly on the wire, not wrapped as an SSLv3 record\r
\r
\r
       uint8 V2CipherSpec[3];\r
\r
\r
       struct {\r
           uint16 msg_length;                                            |\r
           uint8 msg_type;\r
           Version version;\r
           uint16 cipher_spec_length;\r
           uint16 session_id_length;\r
           uint16 challenge_length;\r
           V2CipherSpec cipher_specs[V2ClientHello.cipher_spec_length];\r
           opaque session_id[V2ClientHello.session_id_length];\r
           opaque challenge[V2ClientHello.challenge_length;              |\r
       } V2ClientHello;\r
\r
\r
   msg_length                                                            |\r
       This field is the length of the following data in bytes. The high |\r
       bit MUST be 1 and is not part of the length.                      |\r
\r
\r
   msg_type\r
       This field, in conjunction with the version field, identifies a   |\r
       version 2 client hello message. The value SHOULD be one (1).\r
\r
\r
   version\r
       The highest version of the protocol supported by the client\r
\r
\r
\r
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Dierks & Rescorla            Standards Track                    [Page 74] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
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\r
       (equals ProtocolVersion.version, see Appendix A.1).\r
\r
\r
   cipher_spec_length\r
       This field is the total length of the field cipher_specs. It      |\r
       cannot be zero and MUST be a multiple of the V2CipherSpec length\r
       (3).\r
\r
\r
   session_id_length\r
       This field MUST have a value of zero.                             |\r
\r
\r
   challenge_length\r
       The length in bytes of the client's challenge to the server to    |\r
       authenticate itself. When using the SSLv2 backward compatible     |\r
       handshake the client MUST use a 32-byte challenge.\r
\r
\r
   cipher_specs\r
       This is a list of all CipherSpecs the client is willing and able  |\r
       to use. There MUST be at least one CipherSpec acceptable to the\r
       server.\r
\r
\r
   session_id\r
       This field MUST be empty.                                         |\r
\r
\r
   challenge\r
       The client challenge to the server for the server to identify\r
       itself is a (nearly) arbitrary length random. The TLS server will\r
       right justify the challenge data to become the ClientHello.random\r
       data (padded with leading zeroes, if necessary), as specified in\r
       this protocol specification. If the length of the challenge is\r
       greater than 32 bytes, only the last 32 bytes are used. It is\r
       legitimate (but not necessary) for a V3 server to reject a V2\r
       ClientHello that has fewer than 16 bytes of challenge data.\r
\r
\r
 Note: Requests to resume a TLS session MUST use a TLS client hello.     |\r
\r
\r
E.2. Avoiding man-in-the-middle version rollback\r
\r
\r
   When TLS clients fall back to Version 2.0 compatibility mode, they    |\r
   SHOULD use special PKCS #1 block formatting. This is done so that TLS\r
   servers will reject Version 2.0 sessions with TLS-capable clients.\r
\r
\r
   When TLS clients are in Version 2.0 compatibility mode, they set the\r
   right-hand (least-significant) 8 random bytes of the PKCS padding\r
   (not including the terminal null of the padding) for the RSA\r
   encryption of the ENCRYPTED-KEY-DATA field of the CLIENT-MASTER-KEY\r
   to 0x03 (the other padding bytes are random). After decrypting the    |\r
   ENCRYPTED-KEY-DATA field, servers that support TLS SHOULD issue an\r
   error if these eight padding bytes are 0x03. Version 2.0 servers\r
\r
\r
\r
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Dierks & Rescorla            Standards Track                    [Page 75] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
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   receiving blocks padded in this manner will proceed normally.\r
\r
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Dierks & Rescorla            Standards Track                    [Page 76] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
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F. Security analysis\r
\r
\r
   The TLS protocol is designed to establish a secure connection between\r
   a client and a server communicating over an insecure channel. This\r
   document makes several traditional assumptions, including that\r
   attackers have substantial computational resources and cannot obtain\r
   secret information from sources outside the protocol. Attackers are\r
   assumed to have the ability to capture, modify, delete, replay, and\r
   otherwise tamper with messages sent over the communication channel.\r
   This appendix outlines how TLS has been designed to resist a variety\r
   of attacks.\r
\r
\r
F.1. Handshake protocol\r
\r
\r
   The handshake protocol is responsible for selecting a CipherSpec and\r
   generating a Master Secret, which together comprise the primary\r
   cryptographic parameters associated with a secure session. The\r
   handshake protocol can also optionally authenticate parties who have\r
   certificates signed by a trusted certificate authority.\r
\r
\r
F.1.1. Authentication and key exchange\r
\r
\r
   TLS supports three authentication modes: authentication of both\r
   parties, server authentication with an unauthenticated client, and\r
   total anonymity. Whenever the server is authenticated, the channel is\r
   secure against man-in-the-middle attacks, but completely anonymous\r
   sessions are inherently vulnerable to such attacks.  Anonymous\r
   servers cannot authenticate clients. If the server is authenticated,\r
   its certificate message must provide a valid certificate chain\r
   leading to an acceptable certificate authority.  Similarly,\r
   authenticated clients must supply an acceptable certificate to the\r
   server. Each party is responsible for verifying that the other's\r
   certificate is valid and has not expired or been revoked.\r
\r
\r
   The general goal of the key exchange process is to create a\r
   pre_master_secret known to the communicating parties and not to\r
   attackers. The pre_master_secret will be used to generate the\r
   master_secret (see Section 8.1). The master_secret is required to     |\r
   generate the finished messages, encryption keys, and MAC secrets (see\r
   Sections 7.4.8, 7.4.9 and 6.3). By sending a correct finished\r
   message, parties thus prove that they know the correct\r
   pre_master_secret.\r
\r
\r
F.1.1.1. Anonymous key exchange\r
\r
\r
   Completely anonymous sessions can be established using RSA or Diffie-\r
   Hellman for key exchange. With anonymous RSA, the client encrypts a\r
   pre_master_secret with the server's uncertified public key extracted\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 77] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
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\r
   from the server key exchange message. The result is sent in a client\r
   key exchange message. Since eavesdroppers do not know the server's\r
   private key, it will be infeasible for them to decode the             |\r
   pre_master_secret.                                                    |\r
\r
\r
   Note: No anonymous RSA Cipher Suites are defined in this document.\r
\r
\r
   With Diffie-Hellman, the server's public parameters are contained in\r
   the server key exchange message and the client's are sent in the\r
   client key exchange message. Eavesdroppers who do not know the\r
   private values should not be able to find the Diffie-Hellman result\r
   (i.e. the pre_master_secret).\r
\r
\r
 Warning: Completely anonymous connections only provide protection\r
          against passive eavesdropping. Unless an independent tamper-\r
          proof channel is used to verify that the finished messages\r
          were not replaced by an attacker, server authentication is\r
          required in environments where active man-in-the-middle\r
          attacks are a concern.\r
\r
\r
F.1.1.2. RSA key exchange and authentication\r
\r
\r
   With RSA, key exchange and server authentication are combined. The\r
   public key may be either contained in the server's certificate or may\r
   be a temporary RSA key sent in a server key exchange message.  When\r
   temporary RSA keys are used, they are signed by the server's RSA      |\r
   certificate. The signature includes the current ClientHello.random,\r
   so old signatures and temporary keys cannot be replayed. Servers may\r
   use a single temporary RSA key for multiple negotiation sessions.\r
\r
\r
 Note: The temporary RSA key option is useful if servers need large\r
       certificates but must comply with government-imposed size limits\r
       on keys used for key exchange.\r
\r
\r
   Note that if ephemeral RSA is not used, compromise of the server's    |\r
   static RSA key results in a loss of confidentiality for all sessions  |\r
   protected under that static key. TLS users desiring Perfect Forward   |\r
   Secrecy should use DHE cipher suites. The damage done by exposure of  |\r
   a private key can be limited by changing one's private key (and       |\r
   certificate) frequently.                                              |\r
\r
\r
   After verifying the server's certificate, the client encrypts a\r
   pre_master_secret with the server's public key. By successfully\r
   decoding the pre_master_secret and producing a correct finished\r
   message, the server demonstrates that it knows the private key\r
   corresponding to the server certificate.\r
\r
\r
   When RSA is used for key exchange, clients are authenticated using\r
\r
\r
\r
\r
Dierks & Rescorla            Standards Track                    [Page 78] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
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\r
   the certificate verify message (see Section 7.4.8). The client signs\r
   a value derived from the master_secret and all preceding handshake\r
   messages. These handshake messages include the server certificate,\r
   which binds the signature to the server, and ServerHello.random,\r
   which binds the signature to the current handshake process.\r
\r
\r
F.1.1.3. Diffie-Hellman key exchange with authentication\r
\r
\r
   When Diffie-Hellman key exchange is used, the server can either\r
   supply a certificate containing fixed Diffie-Hellman parameters or\r
   can use the server key exchange message to send a set of temporary\r
   Diffie-Hellman parameters signed with a DSS or RSA certificate.\r
   Temporary parameters are hashed with the hello.random values before\r
   signing to ensure that attackers do not replay old parameters. In\r
   either case, the client can verify the certificate or signature to\r
   ensure that the parameters belong to the server.\r
\r
\r
   If the client has a certificate containing fixed Diffie-Hellman\r
   parameters, its certificate contains the information required to\r
   complete the key exchange. Note that in this case the client and\r
   server will generate the same Diffie-Hellman result (i.e.,\r
   pre_master_secret) every time they communicate. To prevent the\r
   pre_master_secret from staying in memory any longer than necessary,\r
   it should be converted into the master_secret as soon as possible.\r
   Client Diffie-Hellman parameters must be compatible with those\r
   supplied by the server for the key exchange to work.\r
\r
\r
   If the client has a standard DSS or RSA certificate or is\r
   unauthenticated, it sends a set of temporary parameters to the server\r
   in the client key exchange message, then optionally uses a\r
   certificate verify message to authenticate itself.\r
\r
\r
   If the same DH keypair is to be used for multiple handshakes, either  |\r
   because the client or server has a certificate containing a fixed DH  |\r
   keypair or because the server is reusing DH keys, care must be taken  |\r
   to prevent small subgroup attacks. Implementations SHOULD follow the  |\r
   guidelines found in [SUBGROUP].                                       |\r
\r
\r
   Small subgroup attacks are most easily avoided by using one of the    |\r
   DHE ciphersuites and generating a fresh DH private key (X) for each   |\r
   handshake. If a suitable base (such as 2) is chosen, g^X mod p can be |\r
   computed very quickly so the performance cost is minimized.           |\r
   Additionally, using a fresh key for each handshake provides Perfect   |\r
   Forward Secrecy. Implementations SHOULD generate a new X for each     |\r
   handshake when using DHE ciphersuites.                                |\r
\r
\r
F.1.2. Version rollback attacks\r
\r
\r
\r
\r
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Dierks & Rescorla            Standards Track                    [Page 79] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
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\r
   Because TLS includes substantial improvements over SSL Version 2.0,\r
   attackers may try to make TLS-capable clients and servers fall back\r
   to Version 2.0. This attack can occur if (and only if) two TLS-\r
   capable parties use an SSL 2.0 handshake.\r
\r
\r
   Although the solution using non-random PKCS #1 block type 2 message\r
   padding is inelegant, it provides a reasonably secure way for Version\r
   3.0 servers to detect the attack. This solution is not secure against\r
   attackers who can brute force the key and substitute a new ENCRYPTED-\r
   KEY-DATA message containing the same key (but with normal padding)\r
   before the application specified wait threshold has expired. Parties\r
   concerned about attacks of this scale should not be using 40-bit\r
   encryption keys anyway. Altering the padding of the least-significant\r
   8 bytes of the PKCS padding does not impact security for the size of\r
   the signed hashes and RSA key lengths used in the protocol, since\r
   this is essentially equivalent to increasing the input block size by\r
   8 bytes.\r
\r
\r
F.1.3. Detecting attacks against the handshake protocol\r
\r
\r
   An attacker might try to influence the handshake exchange to make the\r
   parties select different encryption algorithms than they would        |\r
   normally chooses. Because many implementations will support 40-bit\r
   exportable encryption and some may even support null encryption or\r
   MAC algorithms, this attack is of particular concern.\r
\r
\r
   For this attack, an attacker must actively change one or more\r
   handshake messages. If this occurs, the client and server will\r
   compute different values for the handshake message hashes. As a\r
   result, the parties will not accept each others' finished messages.\r
   Without the master_secret, the attacker cannot repair the finished\r
   messages, so the attack will be discovered.\r
\r
\r
F.1.4. Resuming sessions\r
\r
\r
   When a connection is established by resuming a session, new\r
   ClientHello.random and ServerHello.random values are hashed with the\r
   session's master_secret. Provided that the master_secret has not been\r
   compromised and that the secure hash operations used to produce the\r
   encryption keys and MAC secrets are secure, the connection should be\r
   secure and effectively independent from previous connections.\r
   Attackers cannot use known encryption keys or MAC secrets to\r
   compromise the master_secret without breaking the secure hash\r
   operations (which use both SHA and MD5).\r
\r
\r
   Sessions cannot be resumed unless both the client and server agree.\r
   If either party suspects that the session may have been compromised,\r
   or that certificates may have expired or been revoked, it should\r
\r
\r
\r
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Dierks & Rescorla            Standards Track                    [Page 80] draft-ietf-tls-rfc2246-bis-06.txt  TLS                        March 2004\r
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   force a full handshake. An upper limit of 24 hours is suggested for\r
   session ID lifetimes, since an attacker who obtains a master_secret\r
   may be able to impersonate the compromised party until the\r
   corresponding session ID is retired. Applications that may be run in\r
   relatively insecure environments should not write session IDs to\r
   stable storage.\r
\r
\r
F.1.5. MD5 and SHA\r
\r
\r
   TLS uses hash functions very conservatively. Where possible, both MD5\r
   and SHA are used in tandem to ensure that non-catastrophic flaws in\r
   one algorithm will not break the overall protocol.\r
\r
\r
F.2. Protecting application data\r
\r
\r
   The master_secret is hashed with the ClientHello.random and\r
   ServerHello.random to produce unique data encryption keys and MAC\r
   secrets for each connection.\r
\r
\r
   Outgoing data is protected with a MAC before transmission. To prevent\r
   message replay or modification attacks, the MAC is computed from the\r
   MAC secret, the sequence number, the message length, the message\r
   contents, and two fixed character strings. The message type field is\r
   necessary to ensure that messages intended for one TLS Record Layer\r
   client are not redirected to another. The sequence number ensures\r
   that attempts to delete or reorder messages will be detected. Since\r
   sequence numbers are 64-bits long, they should never overflow.\r
   Messages from one party cannot be inserted into the other's output,\r
   since they use independent MAC secrets. Similarly, the server-write\r
   and client-write keys are independent so stream cipher keys are used\r
   only once.\r
\r
\r
   If an attacker does break an encryption key, all messages encrypted\r
   with it can be read. Similarly, compromise of a MAC key can make\r
   message modification attacks possible. Because MACs are also\r
   encrypted, message-alteration attacks generally require breaking the\r
   encryption algorithm as well as the MAC.\r
\r
\r
 Note: MAC secrets may be larger than encryption keys, so messages can\r
       remain tamper resistant even if encryption keys are broken.\r
\r
\r
F.3. Explicit IVs                                                        |\r
\r
\r
       [CBCATT] describes a chosen plaintext attack on TLS that depends  |\r
       on knowing the IV for a record. Previous versions of TLS [TLS1.0] |\r
       used the CBC residue of the previous record as the IV and         |\r
       therefore enabled this attack. This version uses an explicit IV   |\r
       in order to protect against this attack.                          |\r
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F.4 Security of Composite Cipher Modes                                   |\r
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       TLS secures transmitted application data via the use of symmetric |\r
       encryption and authentication functions defined in the negotiated |\r
       ciphersuite.  The objective is to protect both the integrity  and |\r
       confidentiality of the transmitted data from malicious actions by |\r
       active attackers in the network.  It turns out that the order in  |\r
       which encryption and authentication functions are applied to the  |\r
       data plays an important role for achieving this goal [ENCAUTH].   |\r
\r
\r
       The most robust method, called encrypt-then-authenticate, first   |\r
       applies encryption to the data and then applies a MAC to the      |\r
       ciphertext.  This method ensures that the integrity and           |\r
       confidentiality goals are obtained with ANY pair of encryption    |\r
       and MAC functions provided that the former is secure against      |\r
       chosen plaintext attacks and the MAC is secure against chosen-    |\r
       message attacks.  TLS uses another method, called authenticate-   |\r
       then-encrypt, in which first a MAC is computed on the plaintext   |\r
       and then the concatenation of plaintext and MAC is encrypted.     |\r
       This method has been proven secure for CERTAIN combinations of    |\r
       encryption functions and MAC functions, but is not guaranteed to  |\r
       be secure in general. In particular, it has been shown that there |\r
       exist perfectly secure encryption functions (secure even in the   |\r
       information theoretic sense) that combined with any secure MAC    |\r
       function fail to provide the confidentiality goal against an      |\r
       active attack.  Therefore, new ciphersuites and operation modes   |\r
       adopted into TLS need to be analyzed under the authenticate-then- |\r
       encrypt method to verify that they achieve the stated integrity   |\r
       and confidentiality goals.                                        |\r
\r
\r
       Currently, the security of the authenticate-then-encrypt method   |\r
       has been proven for some important cases.  One is the case of     |\r
       stream ciphers in which a computationally unpredictable pad of    |\r
       the length of the message plus the length of the MAC tag is       |\r
       produced using a pseudo-random generator and this pad is xor-ed   |\r
       with the concatenation of plaintext and MAC tag.  The other is    |\r
       the case of CBC mode using a secure block cipher.  In this case,  |\r
       security can be shown if one applies one CBC encryption pass to   |\r
       the concatenation of plaintext and MAC and uses a new,            |\r
       independent and unpredictable, IV for each new pair of plaintext  |\r
       and MAC.  In previous versions of SSL, CBC mode was used properly |\r
       EXCEPT that it used a predictable IV in the form of the last      |\r
       block of the previous ciphertext. This made TLS open to chosen    |\r
       plaintext attacks.  This verson of the protocol is immune to      |\r
       those attacks.  For exact details in the encryption modes proven  |\r
       secure see [ENCAUTH].                                             |\r
\r
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F.5 Denial of Service                                                    |\r
\r
\r
       TLS is susceptible to a number of denial of service (DoS)         |\r
       attacks.  In particular, an attacker who initiates a large number |\r
       of TCP connections can cause a server to consume large amounts of |\r
       CPU doing RSA decryption. However, because TLS is generally used  |\r
       over TCP, it is difficult for the attacker to hide his point of   |\r
       origin if proper TCP SYN randomization is used [SEQNUM] by the    |\r
       TCP stack.                                                        |\r
\r
\r
       Because TLS runs over TCP, it is also susceptible to a number of  |\r
       denial of service attacks on individual connections. In           |\r
       particular, attackers can forge RSTs, terminating connections, or |\r
       forge partial TLS records, causing the connection to stall.       |\r
       These attacks cannot in general be defended against by a TCP-     |\r
       using protocol. Implementors or users who are concerned with this |\r
       class of attack should use IPsec AH [AH] or ESP [ESP].            |\r
\r
\r
F.6. Final notes\r
\r
\r
   For TLS to be able to provide a secure connection, both the client\r
   and server systems, keys, and applications must be secure. In\r
   addition, the implementation must be free of security errors.\r
\r
\r
   The system is only as strong as the weakest key exchange and\r
   authentication algorithm supported, and only trustworthy\r
   cryptographic functions should be used. Short public keys, 40-bit\r
   bulk encryption keys, and anonymous servers should be used with great\r
   caution. Implementations and users must be careful when deciding\r
   which certificates and certificate authorities are acceptable; a\r
   dishonest certificate authority can do tremendous damage.\r
\r
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G. Patent Statement\r
\r
\r
   Netscape Communications Corporation (now America Online) has a patent |\r
   claim on the Secure Sockets Layer (SSL) work that this standard is    |\r
   based on. The Internet Standards Process as defined in RFC 2026       |\r
   requests that a statement be obtained from a Patent holder indicating |\r
   that a license will be made available to applicants under reasonable  |\r
   terms and conditions.\r
\r
\r
       Secure Socket Layer Application Program Apparatus And Method\r
       ("SSL"), No. 5,657,390\r
\r
\r
   Netscape Communications has issued the following statement:\r
\r
\r
       Intellectual Property Rights\r
\r
\r
       Secure Sockets Layer\r
\r
\r
       The United States Patent and Trademark Office ("the PTO")\r
       recently issued U.S. Patent No. 5,657,390 ("the SSL Patent")  to\r
       Netscape for inventions described as Secure Sockets Layers\r
       ("SSL"). The IETF is currently considering adopting SSL as a\r
       transport protocol with security features.  Netscape encourages\r
       the royalty-free adoption and use of the SSL protocol upon the\r
       following terms and conditions:\r
\r
\r
         * If you already have a valid SSL Ref license today which\r
           includes source code from Netscape, an additional patent\r
           license under the SSL patent is not required.\r
\r
\r
         * If you don't have an SSL Ref license, you may have a royalty\r
           free license to build implementations covered by the SSL\r
           Patent Claims or the IETF TLS specification provided that you\r
           do not to assert any patent rights against Netscape or other\r
           companies for the implementation of SSL or the IETF TLS\r
           recommendation.\r
\r
\r
       What are "Patent Claims":\r
\r
\r
       Patent claims are claims in an issued foreign or domestic patent\r
       that:\r
\r
\r
        1) must be infringed in order to implement methods or build\r
           products according to the IETF TLS specification;  or\r
\r
\r
        2) patent claims which require the elements of the SSL patent\r
           claims and/or their equivalents to be infringed.\r
\r
\r
\r
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   The Internet Society, Internet Architecture Board, Internet\r
   Engineering Steering Group and the Corporation for National Research\r
   Initiatives take no position on the validity or scope of the patents\r
   and patent applications, nor on the appropriateness of the terms of\r
   the assurance. The Internet Society and other groups mentioned above\r
   have not made any determination as to any other intellectual property\r
   rights which may apply to the practice of this standard.  Any further\r
   consideration of these matters is the user's own responsibility.\r
\r
\r
Security Considerations\r
\r
\r
   Security issues are discussed throughout this memo, especially in     |\r
   Appendices D, E, and F.\r
\r
\r
Normative References                                                     |\r
\r
\r
   [3DES]   W. Tuchman, "Hellman Presents No Shortcut Solutions To DES," |\r
            IEEE Spectrum, v. 16, n. 7, July 1979, pp40-41.\r
\r
\r
   [DES]    ANSI X3.106, "American National Standard for Information\r
            Systems-Data Link Encryption," American National Standards\r
            Institute, 1983.\r
\r
\r
   [DH1]    W. Diffie and M. E. Hellman, "New Directions in\r
            Cryptography," IEEE Transactions on Information Theory, V.\r
            IT-22, n. 6, Jun 1977, pp. 74-84.\r
\r
\r
   [DSS]    NIST FIPS PUB 186, "Digital Signature Standard," National\r
            Institute of Standards and Technology, U.S. Department of\r
            Commerce, May 18, 1994.\r
\r
\r
   [HMAC]   Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-\r
            Hashing for Message Authentication," RFC 2104, February\r
            1997.\r
\r
\r
   [IDEA]   X. Lai, "On the Design and Security of Block Ciphers," ETH\r
            Series in Information Processing, v. 1, Konstanz: Hartung-\r
            Gorre Verlag, 1992.\r
\r
\r
   [MD2]    Kaliski, B., "The MD2 Message Digest Algorithm", RFC 1319,\r
            April 1992.\r
\r
\r
   [MD5]    Rivest, R., "The MD5 Message Digest Algorithm", RFC 1321,\r
            April 1992.\r
\r
\r
   [PKCS1]  RSA Laboratories, "PKCS #1: RSA Encryption Standard,"\r
            version 1.5, November 1993.\r
\r
\r
\r
\r
\r
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   [PKCS6]  RSA Laboratories, "PKCS #6: RSA Extended Certificate Syntax\r
            Standard," version 1.5, November 1993.\r
\r
\r
   [PKCS7]  RSA Laboratories, "PKCS #7: RSA Cryptographic Message Syntax\r
            Standard," version 1.5, November 1993.\r
\r
\r
   [PKIX]   Housley, R., Ford, W., Polk, W. and D. Solo, "Internet\r
            Public Key Infrastructure: Part I: X.509 Certificate and CRL\r
            Profile", RFC 2459, January 1999.\r
\r
\r
   [RC2]    Rivest, R., "A Description of the RC2(r) Encryption\r
            Algorithm", RFC 2268, January 1998.\r
\r
\r
   [RC4]    Thayer, R. and K. Kaukonen, A Stream Cipher Encryption\r
            Algorithm, Work in Progress.\r
\r
\r
   [RSA]    R. Rivest, A. Shamir, and L. M. Adleman, "A Method for\r
            Obtaining Digital Signatures and Public-Key Cryptosystems,"\r
            Communications of the ACM, v. 21, n. 2, Feb 1978, pp.\r
            120-126.\r
\r
\r
   [SHA]    NIST FIPS PUB 180-1, "Secure Hash Standard," National\r
            Institute of Standards and Technology, U.S. Department of\r
            Commerce, Work in Progress, May 31, 1994.\r
\r
\r
   [SSL2]   Hickman, Kipp, "The SSL Protocol", Netscape Communications\r
            Corp., Feb 9, 1995.\r
\r
\r
   [SSL3]   A. Frier, P. Karlton, and P. Kocher, "The SSL 3.0 Protocol",\r
            Netscape Communications Corp., Nov 18, 1996.\r
\r
\r
   [REQ]    Bradner, S., "Key words for use in RFCs to Indicate          |\r
            Requirement Levels", BCP 14, RFC 2119, March 1997.\r
\r
\r
   [TLS1.0] Dierks, T., and Allen, C., "The TLS Protocol, Version 1.0",  |\r
            RFC 2246, January 1999.\r
\r
\r
   [TLSEXT] Blake-Wilson, S., Nystrom, M, Hopwood, D., Mikkelsen, J.,    |\r
            Wright, T., "Transport Layer Security (TLS) Extensions", RFC |\r
            3546, June 2003.\r
   [X509]   CCITT. Recommendation X.509: "The Directory - Authentication\r
            Framework". 1988.\r
\r
\r
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Informative References                                                   |\r
\r
\r
   [AH]     Kent, S., and Atkinson, R., "IP Authentication Header", RFC  |\r
            2402, November 1998.                                         |\r
\r
\r
   [BLEI]   Bleichenbacher D., "Chosen Ciphertext Attacks against        |\r
            Protocols Based on RSA Encryption Standard PKCS #1" in       |\r
            Advances in Cryptology -- CRYPTO'98, LNCS vol. 1462, pages:  |\r
            1-12, 1998.                                                  |\r
\r
\r
   [CBCATT] Moeller, B., "Security of CBC Ciphersuites in SSL/TLS:       |\r
            Problems and Countermeasures",                               |\r
            http://www.openssl.org/~bodo/tls-cbc.txt.                    |\r
\r
\r
   [CBCTIME] Canvel, B., "Password Interception in a SSL/TLS Channel",   |\r
            http://lasecwww.epfl.ch/memo_ssl.shtml, 2003.                |\r
\r
\r
   [ENCAUTH] Krawczyk, H., "The Order of Encryption and Authentication   |\r
            for Protecting Communications (Or: How Secure is SSL?)",     |\r
            Crypto 2001.                                                 |\r
\r
\r
   [ESP]     Kent, S., and Atkinson, R., "IP Encapsulating Security      |\r
            Payload (ESP)", RFC 2406, November 1998.                     |\r
\r
\r
   [FTP]    Postel J., and J. Reynolds, "File Transfer Protocol", STD 9, |\r
            RFC 959, October 1985.                                       |\r
\r
\r
   [HTTP]   Berners-Lee, T., Fielding, R., and H. Frystyk, "Hypertext    |\r
            Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.          |\r
\r
\r
   [KPR03]  Klima, V., Pokorny, O., Rosa, T., "Attacking RSA-based       |\r
            Sessions in SSL/TLS", http://eprint.iacr.org/2003/052/,      |\r
            March 2003.                                                  |\r
   [RSADSI] Contact RSA Data Security, Inc., Tel: 415-595-8782           |\r
\r
\r
   [SCH]    B. Schneier. Applied Cryptography: Protocols, Algorithms,    |\r
            and Source Code in C, Published by John Wiley & Sons, Inc.   |\r
            1994.                                                        |\r
\r
\r
   [SEQNUM] Bellovin. S., "Defending Against Sequence Number Attacks",   |\r
            RFC 1948, May 1996.                                          |\r
\r
\r
   [SUBGROUP] R. Zuccherato, "Methods for Avoiding the Small-Subgroup    |\r
            Attacks on the Diffie-Hellman Key Agreement Method for       |\r
            S/MIME", RFC 2785, March 2000.                               |\r
\r
\r
   [TCP]    Postel, J., "Transmission Control Protocol," STD 7, RFC 793, |\r
            September 1981.                                              |\r
\r
\r
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   [TIMING] Boneh, D., Brumley, D., "Remote timing attacks are           |\r
            practical", USENIX Security Symposium 2003.                  |\r
\r
\r
   [XDR]    R. Srinivansan, Sun Microsystems, RFC-1832: XDR: External\r
            Data Representation Standard, August 1995.\r
\r
\r
\r
Credits                                                                  |\r
\r
\r
   Working Group Chairs                                                  |\r
   Win Treese\r
   EMail: treese@acm.org                                                 |\r
\r
\r
   Eric Rescorla                                                         |\r
   EMail: ekr@rtfm.com                                                   |\r
\r
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   Editors\r
\r
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   Tim Dierks                Eric Rescorla                               |\r
   Google                    RTFM, Inc.                                  |\r
\r
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   EMail: tim@dierks.org         EMail: ekr@rtfm.com                     |\r
\r
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   Other contributors\r
\r
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   Christopher Allen (co-editor of TLS 1.0)                              |\r
   Alacrity Ventures                                                     |\r
   ChristopherA@AlacrityVentures.com                                     |\r
\r
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   Martin Abadi                                                          |\r
   University of California, Santa Cruz                                  |\r
   abadi@cs.ucsc.edu                                                     |\r
\r
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   Ran Canetti                                                           |\r
   IBM                                                                   |\r
   canetti@watson.ibm.com                                                |\r
\r
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   Taher Elgamal                                                         |\r
   taher@securify.com                                                    |\r
   Securify                                                              |\r
\r
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   Anil Gangolli                                                         |\r
   Structured Arts                                                       |\r
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   Kipp Hickman                                                          |\r
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   Phil Karlton (co-author of SSLv3)                                     |\r
\r
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   Paul Kocher (co-author of SSLv3)                                      |\r
   Cryptography Research                                                 |\r
   paul@cryptography.com                                                 |\r
\r
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   Hugo Krawczyk                                                         |\r
   Technion Israel Institute of Technology                               |\r
   hugo@ee.technion.ac.il                                                |\r
\r
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   Robert Relyea                                                         |\r
   Netscape Communications                                               |\r
   relyea@netscape.com                                                   |\r
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   Jim Roskind                                                           |\r
   Netscape Communications                                               |\r
   jar@netscape.com                                                      |\r
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   Michael Sabin                                                         |\r
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   Dan Simon                                                             |\r
   Microsoft, Inc.                                                       |\r
   dansimon@microsoft.com                                                |\r
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   Tom Weinstein                                                         |\r
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Comments\r
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\r
   The discussion list for the IETF TLS working group is located at the\r
   e-mail address <ietf-tls@lists.consensus.com>. Information on the\r
   group and information on how to subscribe to the list is at\r
   <http://lists.consensus.com/>.\r
\r
\r
   Archives of the list can be found at:\r
       <http://www.imc.org/ietf-tls/mail-archive/>\r
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Full Copyright Statement\r
\r
\r
   Copyright (C) The Internet Society (1999).  All Rights Reserved.\r
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   and distributed, in whole or in part, without restriction of any\r
   kind, provided that the above copyright notice and this paragraph are\r
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   document itself may not be modified in any way, such as by removing\r
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