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 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on February 14, 2009. Copyright Notice Copyright (C) The IETF Trust (2008). Hornquist Astrand Expires February 14, 2009 [Page 1] Internet-Draft Kerberos ticket extensions August 2008 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 Hornquist Astrand Expires February 14, 2009 [Page 2] Internet-Draft Kerberos ticket extensions August 2008 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]. Hornquist Astrand Expires February 14, 2009 [Page 3] Internet-Draft Kerberos ticket extensions August 2008 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 Hornquist Astrand Expires February 14, 2009 [Page 4] Internet-Draft Kerberos ticket extensions August 2008 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. Hornquist Astrand Expires February 14, 2009 [Page 5] Internet-Draft Kerberos ticket extensions August 2008 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. Hornquist Astrand Expires February 14, 2009 [Page 6] Internet-Draft Kerberos ticket extensions August 2008 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. Hornquist Astrand Expires February 14, 2009 [Page 7] Internet-Draft Kerberos ticket extensions August 2008 5. Acknowledgements Thanks to Leif Johansson, and Kamada Ken'ichi for reviewing the document and provided suggestions for improvements. Hornquist Astrand Expires February 14, 2009 [Page 8] Internet-Draft Kerberos ticket extensions August 2008 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. Hornquist Astrand Expires February 14, 2009 [Page 9] Internet-Draft Kerberos ticket extensions August 2008 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. Hornquist Astrand Expires February 14, 2009 [Page 10] Internet-Draft Kerberos ticket extensions August 2008 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 Hornquist Astrand Expires February 14, 2009 [Page 11] Internet-Draft Kerberos ticket extensions August 2008 Author's Address Love Hornquist Astrand Apple, Inc Cupertino USA Email: lha@apple.com Hornquist Astrand Expires February 14, 2009 [Page 12] Internet-Draft Kerberos ticket extensions August 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). 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