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Network Working Group                               L. Hornquist Astrand
Internet-Draft                                                Apple, Inc
Intended status: Standards Track                         August 13, 2008
Expires: February 14, 2009


                       Kerberos ticket extensions
                 draft-lha-krb-wg-ticket-extensions-00

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Copyright Notice

   Copyright (C) The IETF Trust (2008).














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Abstract

   The Kerberos protocol does not allow ticket extensions.  This make it
   harder to deploy features like referrals and PKCROSS.

   Since the Kerberos protocol did not specified extensibility for the
   Ticket structure and the current implementations are aware of the
   contents of tickets, the extension protocol cannot simply extend the
   Ticket ASN.1 structure.  Instead, the extension data needs to be
   hidden inside the ticket.


Table of Contents

   1.  Requirements Notation  . . . . . . . . . . . . . . . . . . . .  3
   2.  Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  How to request a new assignment for a ticket extension . . . .  6
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   5.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  8
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   7.  Normative References . . . . . . . . . . . . . . . . . . . . . 10
   Appendix A.  Ticket-extensions ASN.1 Module  . . . . . . . . . . . 11
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
   Intellectual Property and Copyright Statements . . . . . . . . . . 13



























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1.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].














































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2.  Protocol

   The ticket and enc-part as defined by [RFC4120] is defined as follow:


   Ticket          ::= [APPLICATION 1] SEQUENCE {
           tkt-vno         [0] INTEGER (5),
           realm           [1] Realm,
           sname           [2] PrincipalName,
           enc-part        [3] EncryptedData -- EncTicketPart
   }

   EncryptedData   ::= SEQUENCE {
           etype   [0] Int32 -- EncryptionType --,
           kvno    [1] UInt32 OPTIONAL,
           cipher  [2] OCTET STRING -- ciphertext
   }



   This document uses the special encryption type etype-TBETicket to
   signal that enc-part.cipher contains the DER-encoded TBETicket
   structure, instead of an encrypted EncTicketPart.



   etype-TBETicket INTEGER ::= 4711 -- TBA XXX --

   krb5int32  ::= INTEGER (-2147483648..2147483647)

   TBETicket ::= SEQUENCE {
           etype           [0] krb5int32 -- EncryptionType --,
           cipher          [1] OCTET STRING
           extensions      [2] SEQUENCE OF TicketExtension OPTIONAL

   }

   TicketExtension ::= SEQUENCE {
           te-type [0] krb5int32,
           te-data [1] OCTET STRING
           te-csum [2] Checksum OPTIONAL
   }


   The content of cipher data and encryption type fields is moved inside
   TBETicket.

   Negative ticket extensions types (te-type) is private extensions and



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   MUST only be used for experimentation.

   The te-type field is specificing the type of the content in te-data.
   Unknown te-types MUST be ignored both by the client and the server.

   The te-csum field is optional for the type, when in use by type type
   specifed in te-type, the key have to be specifed (usually the session
   key of the ticket) and the key usage number.

   The KDC MUST only return this extension in the AS-REQ if all other
   KDCs for the same realm also supports this extension.

   The KDC MUST only return this extension in the TGS-REQ to server the
   KDC knows supports these extension.  This includes both cross realm
   tickets and service tickets.

   The KDC MAY return extended tickets to servers supporting ticket
   extensions even if the extended ticket does not contain any
   extensions.
































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3.  How to request a new assignment for a ticket extension

   When anyone is writing a internet-draft for which a new assignment
   for te-type is needed/wanted under the ticket extension, then the
   proper way to do so is as follows:


         EXAMPLE-MODULE DEFINITIONS ::= BEGIN

         krb5-ticket-extension-Name ::= INTEGER nnn
         -- IANA: please assign nnn
         -- RFC-Editor: replace nnn with IANA-assigned
         --             number and remove this note
         END


   IANA: Don't do note above, its an example, remove this note RFC-
   Editor: Don't do note above, its an example, remove this note IANA
   will assign the number as part of the RFC publication process.

   When reviewing the document, the reviewer should take sure to check
   that if te-csum is used, the siging key and key usage is specifed.





























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4.  Security Considerations

   This document describes how to extend Kerberos tickets to include
   additional data in the ticket.  This does have a security
   implications since the extension data in the TBETicket is only
   optionally signed, not encrypted and is not replay protected.  It is
   up to the consumers of this interface to make sure its used safely.












































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5.  Acknowledgements

   Thanks to Leif Johansson, and Kamada Ken'ichi for reviewing the
   document and provided suggestions for improvements.















































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6.  IANA Considerations

   There are currently no ticket extensions.  Future ticket extensions
   will be published at:


         http://www.iana.org/assignments/NNNNNNNN
         -- IANA: please name registry, proposal: krb5-ticket-extensions


   IANA is requested to maintain this registry for future assignments.
   New assignments can only be made via Specification Required as
   described in [RFC2434].

   IANA will assign the number as part of the RFC publication process.




































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7.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.

   [RFC4120]  Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
              Kerberos Network Authentication Service (V5)", RFC 4120,
              July 2005.







































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Appendix A.  Ticket-extensions ASN.1 Module



KerberosV5-TicketExtensions {
       iso(1) identified-organization(3) dod(6) internet(1)
       security(5) kerberosV5(2) modules(4) ticket-extensions(TBA)
--- XXX who is the registerar for this number ?
} DEFINITIONS EXPLICIT TAGS ::= BEGIN

IMPORTS
        -- as defined in RFC 4120
        Int32, Checksum
                FROM KerberosV5Spec2 { iso(1) identified-organization(3)
                     dod(6) internet(1) security(5) kerberosV5(2)
                     modules(4) krb5spec2(2) }


etype-TBETicket INTEGER ::= 4711 -- XXX TBA --

TBETicket ::= SEQUENCE {
        etype           [0] Int32 -- EncryptionType --,
        cipher          [1] OCTET STRING
        extensions      [2] SEQUENCE OF TicketExtension OPTIONAL
}

TicketExtension ::= SEQUENCE {
        te-type [0] krb5int32,
        te-data [1] OCTET STRING
        te-csum [2] Checksum
}

END


















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Author's Address

   Love Hornquist Astrand
   Apple, Inc
   Cupertino
   USA

   Email: lha@apple.com











































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