4 Kerberos Working Group K. Raeburn
6 Updates: 4120 (if approved) L. Zhu
7 Intended status: Standards Track Microsoft Corporation
8 Expires: August 28, 2008 February 25, 2008
11 Generating KDC Referrals to Locate Kerberos Realms
12 draft-ietf-krb-wg-kerberos-referrals-10
16 By submitting this Internet-Draft, each author represents that any
17 applicable patent or other IPR claims of which he or she is aware
18 have been or will be disclosed, and any of which he or she becomes
19 aware will be disclosed, in accordance with Section 6 of BCP 79.
21 Internet-Drafts are working documents of the Internet Engineering
22 Task Force (IETF), its areas, and its working groups. Note that
23 other groups may also distribute working documents as Internet-
26 Internet-Drafts are draft documents valid for a maximum of six months
27 and may be updated, replaced, or obsoleted by other documents at any
28 time. It is inappropriate to use Internet-Drafts as reference
29 material or to cite them other than as "work in progress."
31 The list of current Internet-Drafts can be accessed at
32 http://www.ietf.org/ietf/1id-abstracts.txt.
34 The list of Internet-Draft Shadow Directories can be accessed at
35 http://www.ietf.org/shadow.html.
37 This Internet-Draft will expire on August 28, 2008.
41 Copyright (C) The IETF Trust (2008).
45 The memo documents a method for a Kerberos Key Distribution Center
46 (KDC) to respond to client requests for Kerberos tickets when the
47 client does not have detailed configuration information on the realms
48 of users or services. The KDC will handle requests for principals in
49 other realms by returning either a referral error or a cross-realm
50 TGT to another realm on the referral path. The clients will use this
51 referral information to reach the realm of the target principal and
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60 then receive the ticket.
65 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
66 2. Conventions Used in This Document . . . . . . . . . . . . . . 4
67 3. Requesting a Referral . . . . . . . . . . . . . . . . . . . . 4
68 4. Realm Organization Model . . . . . . . . . . . . . . . . . . . 5
69 5. Enterprise Principal Name Type . . . . . . . . . . . . . . . . 5
70 6. Name Canonicalization . . . . . . . . . . . . . . . . . . . . 5
71 7. Client Referrals . . . . . . . . . . . . . . . . . . . . . . . 7
72 8. Server Referrals . . . . . . . . . . . . . . . . . . . . . . . 9
73 9. Cross Realm Routing . . . . . . . . . . . . . . . . . . . . . 11
74 10. Caching Information . . . . . . . . . . . . . . . . . . . . . 11
75 11. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 12
76 12. Number Assignments . . . . . . . . . . . . . . . . . . . . . . 12
77 13. Security Considerations . . . . . . . . . . . . . . . . . . . 13
78 13.1. Shared-password case . . . . . . . . . . . . . . . . . . 13
79 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
80 15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
81 15.1. Normative References . . . . . . . . . . . . . . . . . . 14
82 15.2. Informative References . . . . . . . . . . . . . . . . . 14
83 Appendix A. Compatibility with Earlier Implementations of
84 Name Canonicalization . . . . . . . . . . . . . . . . 14
85 Appendix B. Document history [REMOVE BEFORE PUBLICATION] . . . . 16
86 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
87 Intellectual Property and Copyright Statements . . . . . . . . . . 18
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118 Current implementations of the Kerberos AS and TGS protocols, as
119 defined in [RFC4120], use principal names constructed from a known
120 user or service name and realm. A service name is typically
121 constructed from a name of the service and the DNS host name of the
122 computer that is providing the service. Many existing deployments of
123 Kerberos use a single Kerberos realm where all users and services
124 would be using the same realm. However in an environment where there
125 are multiple trusted Kerberos realms, the client needs to be able to
126 determine what realm a particular user or service is in before making
127 an AS or TGS request. Traditionally this requires client
128 configuration to make this possible.
130 When having to deal with multiple trusted realms, users are forced to
131 know what realm they are in before they can obtain a ticket granting
132 ticket (TGT) with an AS request. However, in many cases the user
133 would like to use a more familiar name that is not directly related
134 to the realm of their Kerberos principal name. A good example of
135 this is an RFC 822 style email name. This document describes a
136 mechanism that would allow a user to specify a user principal name
137 that is an alias for the user's Kerberos principal name. In practice
138 this would be the name that the user specifies to obtain a TGT from a
139 Kerberos KDC. The user principal name no longer has a direct
140 relationship with the Kerberos principal or realm. Thus the
141 administrator is able to move the user's principal to other realms
142 without the user having to know that it happened.
144 Once a user has a TGT, they would like to be able to access services
145 in any trusted Kerberos realm. To do this requires that the client
146 be able to determine what realm the target service principal is in
147 before making the TGS request. Current implementations of Kerberos
148 typically have a table that maps DNS host names to corresponding
149 Kerberos realms. The user-supplied host name or its domain component
150 is looked up in this table (often using the result of some form of
151 host name lookup performed with insecure DNS queries, in violation of
152 [RFC4120]). The corresponding realm is then used to complete the
153 target service principal name.
155 This traditional mechanism requires that each client have very
156 detailed configuration information about the hosts that are providing
157 services and their corresponding realms. Having client side
158 configuration information can be very costly from an administration
159 point of view - especially if there are many realms and computers in
162 There are also cases where specific DNS aliases (local names) have
163 been setup in an organization to refer to a server in another
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172 organization (remote server). The server has different DNS names in
173 each organization and each organization has a Kerberos realm that is
174 configured to service DNS names within that organization. Ideally
175 users are able to authenticate to the server in the other
176 organization using the local server name. This would mean that the
177 local realm be able to produce a ticket to the remote server under
178 its name. The administrator in the local realm could give that
179 remote server an identity in the local realm and then have that
180 remote server maintain a separate secret for each alias it is known
181 as. Alternatively the administrator could arrange to have the local
182 realm issue a referral to the remote realm and notify the requesting
183 client of the server's remote name that should be used in order to
186 This memo proposes a solution for these problems and simplifies
187 administration by minimizing the configuration information needed on
188 each computer using Kerberos. Specifically it describes a mechanism
189 to allow the KDC to handle canonicalization of names, provide for
190 principal aliases for users and services and allow the KDC to
191 determine the trusted realm authentication path by being able to
192 generate referrals to other realms in order to locate principals.
194 Two kinds of KDC referrals are introduced in this memo:
196 1. Client referrals, in which the client doesn't know which realm
197 contains a user account.
198 2. Server referrals, in which the client doesn't know which realm
199 contains a server account.
202 2. Conventions Used in This Document
204 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
205 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
206 document are to be interpreted as described in [RFC2119].
209 3. Requesting a Referral
211 In order to request referrals defined in section 5, 6, and 7, the
212 Kerberos client MUST explicitly request the canonicalize KDC option
213 (bit 15) [RFC4120] for the AS-REQ or TGS-REQ. This flag indicates to
214 the KDC that the client is prepared to receive a reply that contains
215 a principal name other than the one requested.
218 KDCOptions ::= KerberosFlags
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228 -- other KDCOptions values omitted
230 The client should expect, when sending names with the "canonicalize"
231 KDC option, that names in the KDC's reply MAY be different than the
232 name in the request. A referral TGT is a cross realm TGT that is
233 returned with the server name of the ticket being different from the
234 server name in the request [RFC4120].
237 4. Realm Organization Model
239 This memo assumes that the world of principals is arranged on
240 multiple levels: the realm, the enterprise, and the world. A KDC may
241 issue tickets for any principal in its realm or cross-realm tickets
242 for realms with which it has a direct trust relationship. The KDC
243 also has access to a trusted name service that can resolve any name
244 from within its enterprise into a realm. This trusted name service
245 removes the need to use an un-trusted DNS lookup for name resolution.
247 For example, consider the following configuration, where lines
248 indicate trust relationships:
253 ADMIN.EXAMPLE.COM DEV.EXAMPLE.COM
255 In this configuration, all users in the EXAMPLE.COM enterprise could
256 have principal names such as alice@EXAMPLE.COM, with the same realm
257 portion. In addition, servers at EXAMPLE.COM should be able to have
258 DNS host names from any DNS domain independent of what Kerberos realm
259 their principals reside in.
262 5. Enterprise Principal Name Type
264 The NT-ENTERPRISE type principal name contains one component, a
265 string of realm-defined content, which is intended to be used as an
266 alias for another principal name in some realm in the enterprise. It
267 is used for conveying the alias name, not for the real principal
268 names within the realms, and thus is only useful when name
269 canonicalization is requested.
272 6. Name Canonicalization
274 A service or account may have multiple principal names. More useful,
275 though, is a globally unique name that allows unification of email
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284 and security principal names. For example, all users at EXAMPLE.COM
285 may have a client principal name of the form "joe@EXAMPLE.COM" even
286 though the principals are contained in multiple realms. This global
287 name is again an alias for the true client principal name, which
288 indicates what realm contains the principal. Thus, accounts "alice"
289 in the realm DEV.EXAMPLE.COM and "bob" in ADMIN.EXAMPLE.COM may log
290 on as "alice@EXAMPLE.COM" and "bob@EXAMPLE.COM".
292 This utilizes a new client principal name type, as the AS-REQ message
293 only contains a single realm field, and the realm portion of this
294 name corresponds to the Kerberos realm with which the request is
295 made. Thus, the entire name "alice@EXAMPLE.COM" is transmitted as a
296 single component in the client name field of the AS-REQ message, with
297 a name type of NT-ENTERPRISE [RFC4120] (and the local realm name).
298 The KDC will recognize this name type and then transform the
299 requested name into the true principal name if the client account
300 resides in the local realm. The true principal name can have a name
301 type different from the requested name type. Typically the true
302 principal name will be a NT-PRINCIPAL [RFC4120].
304 If the "canonicalize" KDC option is set, then the KDC MAY change the
305 client principal name and type in the AS response and ticket returned
306 from the name type of the client name in the request, and include a
307 mandatory PA-DATA object authenticating the client name mapping:
309 ReferralInfo ::= SEQUENCE {
310 requested-name [0] PrincipalName,
311 mapped-name [1] PrincipalName,
314 PA-CLIENT-CANONICALIZED ::= SEQUENCE {
315 names [0] ReferralInfo,
316 canon-checksum [1] Checksum
319 The canon-checksum field is computed over the DER encoding of the
320 names sequences, using the AS reply key and a key usage value of
323 If the client name is unchanged, the PA-CLIENT-CANONICALIZED data is
324 not included. If the client name is changed, and the PA-CLIENT-
325 CANONICALIZED field does not exist, or the checksum cannot be
326 verified, or the requested-name field doesn't match the client name
327 in the originally-transmitted request, the client should discard the
330 For example the AS request may specify a client name of "bob@
331 EXAMPLE.COM" as an NT-ENTERPRISE name with the "canonicalize" KDC
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340 option set and the KDC will return with a client name of "104567" as
341 a NT-UID, and a PA-CLIENT-CANONICALIZED field listing the NT-
342 ENTERPRISE "bob@EXAMPLE.COM" principal as the requested-name and the
343 NT-UID "104567" principal as the mapped-name.
345 (It is assumed that the client discovers whether the KDC supports the
346 NT-ENTERPRISE name type via out of band mechanisms.)
348 In order to enable one party in a user-to-user exchange to confirm
349 the identity of another when only the alias is known, the KDC MAY
350 include the following authorization data element, wrapped in AD-KDC-
351 ISSUED, in the initial credentials and copy it from a ticket-granting
352 ticket into additional credentials:
354 AD-LOGIN-ALIAS ::= SEQUENCE { -- ad-type number TBD --
355 login-aliases [0] SEQUENCE(1..MAX) OF PrincipalName,
358 The login-aliases field lists one or more of the aliases the
359 principal may have used in the initial ticket request.
361 The recipient of this authenticator must check the AD-LOGIN-ALIAS
362 names, if present, in addition to the normal client name field,
363 against the identity of the party with which it wishes to
364 authenticate; either should be allowed to match. (Note that this is
365 not backwards compatible with [RFC4120]; if the server side of the
366 user-to-user exchange does not support this extension, and does not
367 know the true principal name, authentication may fail if the alias is
368 sought in the client name field.)
370 The use of AD-KDC-ISSUED authorization data elements in cross-realm
371 cases has not been well explored at this writing; hence we will only
372 specify the inclusion of this data in the one-realm case. The alias
373 information should be dropped in the general cross-realm case.
374 However, a realm may implement a policy of accepting and re-signing
375 (wrapping in a new AD-KDC-ISSUED element) alias information provided
376 by certain other realms in the cross-realm ticket-granting service.
381 The simplest form of ticket referral is for a user requesting a
382 ticket using an AS-REQ. In this case, the client machine will send
383 the AS-REQ to a convenient trusted realm, for example the realm of
384 the client machine. In the case of the name alice@EXAMPLE.COM, the
385 client MAY optimistically choose to send the request to EXAMPLE.COM.
386 The realm in the AS-REQ is always the name of the realm that the
387 request is for as specified in [RFC4120].
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396 The KDC will try to lookup the name in its local account database.
397 If the account is present in the realm of the request, it SHOULD
398 return a KDC reply structure with the appropriate ticket.
400 If the account is not present in the realm specified in the request
401 and the "canonicalize" KDC option is set, the KDC will try to lookup
402 the entire name, alice@EXAMPLE.COM, using a name service. If this
403 lookup is unsuccessful, it MUST return the error
404 KDC_ERR_C_PRINCIPAL_UNKNOWN [RFC4120]. If the lookup is successful,
405 it MUST return an error KDC_ERR_WRONG_REALM [RFC4120] and in the
406 error message the crealm field will contain either the true realm of
407 the client or another realm that MAY have better information about
408 the client's true realm. The client SHALL NOT use a cname returned
409 from a Kerberos error until that name is validated.
411 If the client receives a KDC_ERR_WRONG_REALM error, it will issue a
412 new AS request with the same client principal name used to generate
413 the first referral to the realm specified by the realm field of the
414 Kerberos error message corresponding to the first request. (The
415 client realm name will be updated in the new request to refer to this
416 new realm.) The client SHOULD repeat these steps until it finds the
417 true realm of the client. To avoid infinite referral loops, an
418 implementation should limit the number of referrals. A suggested
419 limit is 5 referrals before giving up.
421 Since the same client name is sent to the referring and referred-to
422 realms, both realms must recognize the same client names. In
423 particular, the referring realm cannot (usefully) define principal
424 name aliases that the referred-to realm will not know.
426 The true principal name of the client, returned in AS-REQ, can be
427 validated in a subsequent TGS message exchange where its value is
428 communicated back to the KDC via the authenticator in the PA-TGS-REQ
429 padata [RFC4120]. However, this requires trusting the referred-to
430 realm's KDCs. Clients should limit the referral mappings they will
431 accept to realms trusted via some local policy. Some possible
432 factors that might be taken into consideration for such a policy
435 o Any realm indicated by the local KDC, if the returned KRB-ERROR
436 message is protected, for example using a public key known to be
437 associated with the KDC
438 o A list of realms configured by an administrator
439 o Any realm accepted by the user when explicitly prompted
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454 The primary difference in server referrals is that the KDC MUST
455 return a referral TGT rather than an error message as is done in the
456 client referrals. There needs to be a place to include in the reply
457 information about what realm contains the server. This is done by
458 returning information about the server name in the pre-authentication
459 data field of the KDC reply [RFC4120], as specified later in this
462 If the KDC resolves the server principal name into a principal in the
463 realm specified by the service realm name, it will return a normal
466 If the "canonicalize" flag in the KDC options is not set, the KDC
467 MUST only look up the name as a normal principal name in the
468 specified server realm. If the "canonicalize" flag in the KDC
469 options is set and the KDC doesn't find the principal locally, the
470 KDC MAY return a cross-realm ticket granting ticket to the next hop
471 on the trust path towards a realm that may be able to resolve the
472 principal name. The true principal name of the server SHALL be
473 returned in the padata of the reply if it is different from what is
474 specified the request.
476 When a referral TGT is returned, the KDC MUST return the target realm
477 for the referral TGT as an KDC supplied pre-authentication data
478 element in the response. This referral information in pre-
479 authentication data MUST be encrypted using the session key from the
480 reply ticket. The key usage value for the encryption operation used
481 by PA-SERVER-REFERRAL is 26.
483 The pre-authentication data returned by the KDC, which contains the
484 referred realm and the true principal name of server, is encoded in
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508 PA-SERVER-REFERRAL 25
510 PA-SERVER-REFERRAL-DATA ::= EncryptedData
511 -- ServerReferralData --
513 ServerReferralData ::= SEQUENCE {
514 referred-realm [0] Realm OPTIONAL,
515 -- target realm of the referral TGT
516 true-principal-name [1] PrincipalName OPTIONAL,
517 -- true server principal name
518 requested-principal-name [2] PrincipalName OPTIONAL,
519 -- requested server name
520 referral-valid-until [3] KerberosTime OPTIONAL,
524 Clients SHALL NOT accept a reply ticket in which the server principal
525 name is different from that of the request, if the KDC response does
526 not contain a PA-SERVER-REFERRAL padata entry.
528 The requested-principal-name MUST be included by the KDC, and MUST be
529 verified by the client, if the client sent an AS-REQ, as protection
530 against a man-in-the-middle modification to the AS-REQ message.
532 The referred-realm field is present if and only if the returned
533 ticket is a referral TGT, not a service ticket for the requested
536 When a referral TGT is returned and the true-principal-name field is
537 present, the client MUST use that name in the subsequent requests to
538 the server realm when following the referral.
540 Client SHALL NOT accept a true server principal name for a service
541 ticket if the true-principal-name field is not present in the PA-
542 SERVER-REFERRAL data.
544 The client will use this referral information to request a chain of
545 cross-realm ticket granting tickets until it reaches the realm of the
546 server, and can then expect to receive a valid service ticket.
548 However an implementation should limit the number of referrals that
549 it processes to avoid infinite referral loops. A suggested limit is
550 5 referrals before giving up.
552 The client may cache the mapping of the requested name to the name of
553 the next realm to use and the principal name to ask for. (See
554 Section 10.) The referral-valid-until field, if present, conveys how
555 long this information is valid for.
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564 Here is an example of a client requesting a service ticket for a
565 service in realm DEV.EXAMPLE.COM where the client is in
568 +NC = Canonicalize KDCOption set
569 +PA-REFERRAL = returned PA-SERVER-REFERRAL
570 C: TGS-REQ sname=http/foo.dev.example.com +NC to ADMIN.EXAMPLE.COM
571 S: TGS-REP sname=krbtgt/EXAMPLE.COM@ADMIN.EXAMPLE.COM +PA-REFERRAL
572 containing EXAMPLE.COM as the referred realm with no
574 C: TGS-REQ sname=http/foo.dev.example.com +NC to EXAMPLE.COM
575 S: TGS-REP sname=krbtgt/DEV.EXAMPLE.COM@EXAMPLE.COM +PA-REFERRAL
576 containing DEV.EXAMPLE.COM as the referred realm with no
578 C: TGS-REQ sname=http/foo.dev.example.com +NC to DEV.EXAMPLE.COM
579 S: TGS-REP sname=http/foo.dev.example.com@DEV.EXAMPLE.COM
581 Note that any referral or alias processing of the server name in
582 user-to-user authentication should use the same data as client name
583 canonicalization or referral. Otherwise, the name used by one user
584 to log in may not be useable by another for user-to-user
585 authentication to the first.
588 9. Cross Realm Routing
590 The current Kerberos protocol requires the client to explicitly
591 request a cross-realm TGT for each pair of realms on a referral
592 chain. As a result, the client need to be aware of the trust
593 hierarchy and of any short-cut trusts (those that aren't parent-
596 Instead, using the server referral routing mechanism as defined in
597 Section 8, The KDC will determine the best path for the client and
598 return a cross-realm TGT as the referral TGT, and the target realm
599 for this TGT in the PA-SERVER-REFERRAL of the KDC reply.
601 If the "canonicalize" KDC option is not set, the KDC SHALL NOT return
602 a referral TGT. Clients SHALL NOT process referral TGTs if the KDC
603 response does not contain the PA-SERVER-REFERRAL padata.
606 10. Caching Information
608 It is possible that the client may wish to get additional credentials
609 for the same service principal, perhaps with different authorization-
610 data restrictions or other changed attributes. The return of a
611 server referral from a KDC can be taken as an indication that the
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620 requested principal does not currently exist in the local realm.
621 Clearly, it would reduce network traffic if the clients could cache
622 that information and use it when acquiring the second set of
623 credentials for a service, rather than always having to re-check with
624 the local KDC to see if the name has been created locally.
626 If the referral-valid-until field is provided in the PA-SERVER-
627 REFERRAL-DATA message, it indicates the expiration time of this data;
628 if it is not included, the expiration time of the TGT is used. When
629 the TGT expires, the previously returned referral from the local KDC
630 should be considered invalid, and the local KDC must be asked again
631 for information for the desired service principal name. (Note that
632 the client may get back multiple referral TGTs from the local KDC to
633 the same remote realm, with different lifetimes. The lifetime
634 information must be properly associated with the requested service
635 principal names. Simply having another TGT for the same remote realm
636 does not extend the validity of previously acquired information about
637 one service principal name.) If the client is still in contact with
638 the service and needs to reauthenticate to the same service
639 regardless of local service principal name assignments, it should use
640 the referred-realm and true-principal-name values when requesting new
643 Accordingly, KDC authors and maintainers should consider what factors
644 (e.g., DNS alias lifetimes) they may or may not wish to incorporate
645 into credential expiration times in cases of referrals.
650 Client referral info validation
652 When should client name aliases be included in credentials? Should
653 all known client name aliases be included, or only the one used at
654 initial ticket acquisition?
656 Should list the policies that need to be defined.
658 More examples: u2u, policy checks, maybe cross-realm.
660 Restore server name canonicalization from early drafts.
663 12. Number Assignments
665 Most number registries in the Kerberos protocol have not been turned
666 over to IANA for management at the time of this writing, hence this
667 is not an "IANA Considerations" section.
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676 Various values do need assigning for this draft:
678 PA-CLIENT-CANONICALIZED
679 key usage value for PA-CLIENT-CANONICALIZED field canon-checksum
682 13. Security Considerations
684 For the AS exchange case, it is important that the logon mechanism
685 not trust a name that has not been used to authenticate the user.
686 For example, the name that the user enters as part of a logon
687 exchange may not be the name that the user authenticates as, given
688 that the KDC_ERR_WRONG_REALM error may have been returned. The
689 relevant Kerberos naming information for logon (if any), is the
690 client name and client realm in the service ticket targeted at the
691 workstation that was obtained using the user's initial TGT.
693 How the client name and client realm is mapped into a local account
694 for logon is a local matter, but the client logon mechanism MUST use
695 additional information such as the client realm and/or authorization
696 attributes from the service ticket presented to the workstation by
697 the user, when mapping the logon credentials to a local account on
700 13.1. Shared-password case
702 A special case to examine is when the user is known (or correctly
703 suspected) to use the same password for multiple accounts. A man-in-
704 the-middle attacker can either alter the request on its way to the
705 KDC, changing the client principal name, or reply to the client with
706 a response previously send by the KDC in response to a request from
707 the attacker. The response received by the client can then be
708 decrypted by the user, though if the default "salt" generated from
709 the principal name is used to produce the user's key, a PA-ETYPE-INFO
710 or PA-ETYPE-INFO2 preauth record may need to be added or altered by
711 the attacker to cause the client software to generate the key needed
712 for the message it will receive. None of this requires the attacker
713 to know the user's password, and without further checking, could
714 cause the user to unknowingly use the wrong credentials.
716 In normal [RFC4120] operation, a generated AP-REQ message includes in
717 the Authenticator field a copy of the client's idea of its own
718 principal name. If this differs from the name in the KDC-generated
719 Ticket, the application server will reject the message.
721 With client name canonicalization as described in this document, the
722 client may get its principal name from the response from the KDC.
723 Requiring the PA-CLIENT-CANONICALIZED data lets the client securely
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732 check that the requested name was not altered in transit. If the PA-
733 CLIENT-CANONICALIZED data is absent, the client can use the principal
739 Sam Hartman and authors came up with the idea of using the ticket key
740 to encrypt the referral data, which prevents cut and paste attack
741 using the referral data and referral TGTs.
743 John Brezak, Mike Swift, and Jonathan Trostle wrote the initial
744 version of this document.
746 Karthik Jaganathan contributed to earlier versions.
751 15.1. Normative References
753 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
754 Requirement Levels", BCP 14, RFC 2119, March 1997.
756 [RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
757 Kerberos Network Authentication Service (V5)", RFC 4120,
760 15.2. Informative References
762 [RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
763 X.509 Public Key Infrastructure Certificate and
764 Certificate Revocation List (CRL) Profile", RFC 3280,
767 [RFC4556] Zhu, L. and B. Tung, "Public Key Cryptography for Initial
768 Authentication in Kerberos (PKINIT)", RFC 4556, June 2006.
770 [XPR] Trostle, J., Kosinovsky, I., and M. Swift, "Implementation
771 of Crossrealm Referral Handling in the MIT Kerberos
772 Client", Network and Distributed System Security
773 Symposium, February 2001.
776 Appendix A. Compatibility with Earlier Implementations of Name
779 The Microsoft Windows 2000 and Windows 2003 releases included an
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785 Internet-Draft KDC Referrals February 2008
788 earlier form of name-canonicalization [XPR]. Here are the
791 1) The TGS referral data is returned inside of the KDC message as
792 "encrypted pre-authentication data".
796 EncKDCRepPart ::= SEQUENCE {
797 key [0] EncryptionKey,
798 last-req [1] LastReq,
800 key-expiration [3] KerberosTime OPTIONAL,
801 flags [4] TicketFlags,
802 authtime [5] KerberosTime,
803 starttime [6] KerberosTime OPTIONAL,
804 endtime [7] KerberosTime,
805 renew-till [8] KerberosTime OPTIONAL,
807 sname [10] PrincipalName,
808 caddr [11] HostAddresses OPTIONAL,
809 encrypted-pa-data [12] SEQUENCE OF PA-DATA OPTIONAL
812 2) The preauth data type definition in the encrypted preauth data is
817 PA-SVR-REFERRAL-INFO 20
819 PA-SVR-REFERRAL-DATA ::= SEQUENCE {
820 referred-name [1] PrincipalName OPTIONAL,
821 referred-realm [0] Realm
824 3) When PKINIT ([RFC4556]) is used, the NT-ENTERPRISE client name is
825 encoded as a Subject Alternative Name (SAN) extension [RFC3280] in
826 the client's X.509 certificate. The type of the otherName field
827 for this SAN extension is AnotherName [RFC3280]. The type-id
828 field of the type AnotherName is id-ms-sc-logon-upn
829 (1.3.6.1.4.1.311.20.2.3) and the value field of the type
830 AnotherName is a KerberosString [RFC4120]. The value of this
831 KerberosString type is the single component in the name-string
832 [RFC4120] sequence for the corresponding NT-ENTERPRISE name type.
834 In Microsoft's current implementation through the use of global
835 catalogs any domain in one forest is reachable from any other domain
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841 Internet-Draft KDC Referrals February 2008
844 in the same forest or another trusted forest with 3 or less
845 referrals. A forest is a collection of realms with hierarchical
846 trust relationships: there can be multiple trust trees in a forest;
847 each child and parent realm pair and each root realm pair have
848 bidirectional transitive direct rusts between them.
850 While we might want to permit multiple aliases to exist and even be
851 reported in AD-LOGIN-ALIAS, the Microsoft implementation permits only
852 one NT-ENTERPRISE alias to exist, so this question had not previously
856 Appendix B. Document history [REMOVE BEFORE PUBLICATION]
859 09 Changed to EXAMPLE.COM instead of using Morgan Stanley's domain.
860 Rewrote description of existing practice. (Don't name the lookup
861 table consulted. Mention that DNS "canonicalization" is contrary
862 to [RFC4120].) Noted Microsoft behavior should be moved out into
863 a separate document. Changed some second-person references in the
864 introduction to identify the proper parties. Changed PA-CLIENT-
865 CANONICALIZED to use a separate type for the actual referral data,
866 add an extension marker to that type, and change the checksum key
867 from the "returned session key" to the "AS reply key". Changed
868 AD-LOGIN-ALIAS to contain a sequence of names, to be contained in
869 AD-KDC-ISSUED instead of AD-IF-RELEVANT, and to drop the no longer
870 needed separate checksum. Attempt to clarify the cache lifetime
871 of referral information.
872 08 Moved Microsoft implementation info to appendix. Clarify lack of
873 local server name canonicalization. Added optional authz-data for
874 login alias, to support user-to-user case. Added requested-
875 principal-name to ServerReferralData. Added discussion of caching
876 information, and referral TGT lifetime.
877 07 Re-issued with new editor. Fixed up some references. Started
884 Massachusetts Institute of Technology
885 77 Massachusetts Avenue
889 Email: raeburn@mit.edu
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897 Internet-Draft KDC Referrals February 2008
901 Microsoft Corporation
906 Email: lzhu@microsoft.com
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953 Internet-Draft KDC Referrals February 2008
956 Full Copyright Statement
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