INTERNET-DRAFT S. Santesson (Microsoft) Intended Category: Standards Track A. Medvinsky (Microsoft) Expires June 2007 J. Altman (Secure Endpoints) December 2006 Generic Security Service Application Program Interface (GSS-API) Extension for Transport Layer Security (TLS) 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/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Abstract This document defines protocol extensions to the Transport Layer Security (TLS) protocol for user authentication and key negotiation based on the Generic Security Service Application Program Interface (GSS-API). Full flexibility for negotiation of GSS-API mechanisms is provided, allowing use of arbitrary GSS-API mechanisms provided that they support the GSS-API PRF. This document supersedes RFC 2712 [ref] as the mechanism to support Kerberos based authentication and key establishment for a TLS session. Santesson, et. all [Page 1] INTERNET DRAFT DNS SRV RR otherName November 2006 Table of Contents 1 Introduction ................................................ n 2 GSS-API TLS extension ....................................... n 3 GSS-API Handshake message ................................... n 4 Cipher Suites ............................................... n 4 Message Flow ............................................... n 5 Key Derivation .............................................. n 6 Security Considerations ..................................... n 7 IANA Considerations ......................................... n 8 References .................................................. n Appendix A (if needed) ........................................ n Authors' Addresses ............................................. n Full Copyright Statement ....................................... n Intellectual Property .......................................... n 1. Introduction This document defines protocol extensions to the Transport Layer Security (TLS) [N5] protocol for user authentication and key negotiation based on the Generic Security Service Application Program Interface (GSS-API). The extensions to TLS include a new ExtensionType "gss_api" (section 2), a new HandshakeType "gss_token" (section 3), a new KeyExchangeAlgorithm "gss_prf" (section 5), and new "TLS_GSS" cipher suites (section 4). Full flexibility for negotiation of GSS-API mechanisms is provided, allowing use of arbitrary GSS-API mechanisms provided that they support the GSS-API PRF. This document supersedes RFC 2712 [ref] as the mechanism to support Kerberos based authentication and key establishment for a TLS session. 1.1 Terminology 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 RFC 2119 [N1]. The syntax for the supplemental_data handshake message is defined using the TLS Presentation Language, which is specified in Section 4 of [N4]. Santesson, et. all [Page 2] INTERNET DRAFT DNS SRV RR otherName November 2006 2. GSS-API TLS extension This section defines a new TLS extension that conveys a list of GSS mechanism OIDS in ClientHello and ServerHello messages. The client uses this extension to transmit a list of supported GSS mechanisms to the server. If the server chooses one of the GSS mechanisms, it returns the selected OID to the client. The client includes this extension in the ClientHello only if one or more GSS based ciphersuites (defined in section X) are included in the list of supported cipher suites. Similarly, the server includes this extension in the ServerHello message only if it selected one of the GSS cipher suites. enum { gss_api(n), (65535) } ExtensionType; The "extension_data" field of this extension SHALL contain "GssOIDList" where: struct{ GssOID gss_oid_list<0..2^24-1> // list of supported OIDs }GssOIDList; unit16 GssOID<2..254>; GssOID contains a sequence of integers of an OBJECT IDENTIFIER (OID) [ref] where the first integer in the sequence specifies the top node of the OID. Each OID specifies a specific GSS token exchange scheme. 3. GSS-API Handshake Message This section defines a new handshake message to carry GSS tokens. The message is used to send GSS tokens from TLS client to TLS server and vice versa. enum { gss_token (nn), (255) } HandshakeType; struct { HandshakeType msg_type; /* handshake type */ uint24 length; /* octets in message */ select (HandshakeType) { Santesson, et. all [Page 3] INTERNET DRAFT DNS SRV RR otherName November 2006 case gss_token: GssToken; } body; } Handshake; Struct { opaque GssPayload<1..2^16-1>; opaque GssStatus[1] } GssToken; The GssStatus contains a status byte for the GssPayload: GssStatus GSS_NORMAL = { 0x00 }; GssStatus GSS_LAST_PAYLOAD = { 0x01 }; GssStatus GSS_ERROR = { 0x02 }; GSS_NORMAL is set for all GssPayload that does not match the conditions for any other status bytes. GSS_LAST_PAYLOAD is set for the last GssPayload in the exchange of GSS-API payloads and signals that the exchange was successfully concluded. GSS_ERROR is set if an error state was reached in the exchange of GSS tokens. Receiving a GssToken with this status set results in a fatal error, and the receiver MUST close the connection with a handshake_failure alert. Immediately following the transmission of a GssToken with this status set, the sender MUST close the connection with a handshake_failure alert. 4. Cipher suites This document defines the following new cipher suites CipherSuite TLS_GSS_API_WITH_RC4_128_SHA = { 0xnn,0x00 }; CipherSuite TLS_GSS_API_WITH_AES_128_CBC_SHA = { 0xnn,0x01 }; CipherSuite TLS_GSS_API_WITH_AES_256_CBC_SHA = { 0xnn,0x02 }; 5. Key Derivation After successful completion of the gss_token messages, the client and server each obtain 46 bytes of key random data using the GSS-API PRF. This data is the TLS pre-master secret. Santesson, et. all [Page 4] INTERNET DRAFT DNS SRV RR otherName November 2006 If the GSS-API PRF fails, the connection MUST be closed with a handshake_failure alert. 6. Message flow Client Server ClientHello /* with GSS-API extension */ -----> ServerHello /* with GSS-API extension */ <-------- ServerHelloDone <----- gss_token Handskake messages -----> /* multiple iterations with GssPayload */ ClientKeyExchange [ChangeCipherSpec] Finished --------> [ChangeCipherSpec] <-------- Finished Application Data <-------> Application Data If the client is sending the GSSToken message with the GSS_LAST_PAYLOAD flag set then the third leg of the protocol would look like this: GSSToken ClientKeyExchange [ChangeCipherSpec] Finished However, for a GSS scheme where the server is sending the last GSS token to the client (and the client has no more GSS tokens to send then the third leg of the protocol will be just: ClientKeyExchange [ChangeCipherSpec] Finished 7 IANA Considerations IANA needs to take the following actions: 1) Create an entry, gss_api (TBD), in the existing registry for ExtensionType (defined in RFC 4366 [N7]). 2) Create an entry, gss_token (TBD), in the existing registry for HandshakeType (defined in RFC 2246 [N7]). Santesson, et. all [Page 5] INTERNET DRAFT DNS SRV RR otherName November 2006 Cipher suite IANA actions TBD 8 References Normative references: [N1] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [N2] Linn, J., "Generic Security Service Application Program Interface Version 2, Update 1", RFC 2743, January 2000. [N3] N. Williams, "A Pseudo-Random Function (PRF) API Extension for theGeneric Security Service Application Program Interface (GSS-API)",RFC 4401, February 2006. [N4] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC 2246, January 1999. [N5] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.1", RFC 4346, April 2006. [N6] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., and T. Wright, "Transport Layer Security (TLS) Extensions", RFC 4366, April 2006. [N7] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. Santesson, et. all [Page 6] INTERNET DRAFT DNS SRV RR otherName November 2006 Appendix A. Appednix text Santesson, et. all [Page 7] INTERNET DRAFT DNS SRV RR otherName November 2006 Authors' Addresses Stefan Santesson Microsoft Tuborg Boulevard 12 2900 Hellerup Denmark EMail: stefans@microsoft.com Ari Medvinsky Microsoft One Microsoft Way Redmond, WA 98052-6399 USA Email: arimed(at)microsoft.com Jeffrey E. Altman Secure Endpoints Inc. 255 West 94th Street New York NY 10025 USA EMail:jaltman@columbia.edu Santesson, et. all [Page 8] INTERNET DRAFT DNS SRV RR otherName November 2006 Full Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org." Expires June 2007 Santesson, et. all [Page 9]