Network Working Group S. Josefsson Internet-Draft November 12, 2005 Updates: 4120 (if approved) Expires: May 16, 2006 Kerberos 5 TCP/IP Expansion Mechanism draft-josefsson-krb-tcp-expansion-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 May 16, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract An expansion mechanism for the Kerberos 5 TCP/IP Transport is described. Josefsson Expires May 16, 2006 [Page 1]
Internet-Draft Kerberos 5 TCP/IP Expansion Mechanism November 2005 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions used in this document . . . . . . . . . . . . . . . 3 3. Expansion Mechanism for TCP/IP transport . . . . . . . . . . . 3 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 6. Copying conditions . . . . . . . . . . . . . . . . . . . . . . 5 7. Normative References . . . . . . . . . . . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6 Intellectual Property and Copyright Statements . . . . . . . . . . 7 Josefsson Expires May 16, 2006 [Page 2]
Internet-Draft Kerberos 5 TCP/IP Expansion Mechanism November 2005 1. Introduction The Kerberos 5 [3] specification reserve the high order bit in the length field for TCP/IP transport for future expansion. This document update [3] to describe the behaviour when that bit is set. The required behaviour for clients and KDCs regarding the reserved bit was specified as follows in section 7.2.2 of [3]: Each request (KRB_KDC_REQ) and response (KRB_KDC_REP or KRB_ERROR) sent over the TCP stream is preceded by the length of the request as 4 octets in network byte order. The high bit of the length is reserved for future expansion and MUST currently be set to zero. If a KDC that does not understand how to interpret a set high bit of the length encoding receives a request with the high order bit of the length set, it MUST return a KRB-ERROR message with the error KRB_ERR_FIELD_TOOLONG and MUST close the TCP stream. This document describe how the high bit is used to implement an expansion mechanism. This expansion mechanism is intended for features that are specific for the TCP/IP transport. 2. Conventions used in this document 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 [1]. 3. Expansion Mechanism for TCP/IP transport Kerberos 5 require Key Distribution Centers (KDCs) to accept requests over TCP. Each request and response is prefixed by 4 octets, encoding an integer in network byte order, that indicate the length of the packet. The high bit of the 4 octet length field was reserved for future expansion. Servers that do not understand how to interpret a set high bit are required to return a KRB-ERROR with the KRB_ERR_FIELD_TOOLONG error code, and to close the TCP stream. We will use the reserved bit to provide an expansion mechanism. When the reserved high bit is set, the remaining 31 bits of the 4 octets are treated as an extensible typed hole, and thus form a 31 bit integer enumerating various expansions. Each of the values indicate a specific extended operation mode, which are to be described elsewhere. Josefsson Expires May 16, 2006 [Page 3]
Internet-Draft Kerberos 5 TCP/IP Expansion Mechanism November 2005 If the KDC do not understand a requested expansion, it MUST return a KRB-ERROR with a KRB_ERR_FIELD_TOOLONG value (prefixed by the 4 octet length integer, with the high bit clear, as usual) and close the TCP stream. The following table specify the meaning of the 31 lower bits in the 4 octet field, when the high bit is set: 0 RESERVED. 1...2147483647 AVAILABLE for registration, through IANA. 2147483648 RESERVED. Each expansion mechanism MUST describe the structure of protocol data beyond the length field, and also the behaviour of the client and KDC. 4. Security Considerations Because the initial length field is not protected, it is possible for an active attacker (i.e., one that is able to modify traffic between the client and the KDC) to make it appear to the client that the server do not support this expansion. Client and KDC policies can be used to reject connections that do not use any expansion. 5. IANA Considerations IANA needs to create a new registry for "Kerberos 5 TCP/IP Expansions". The initial contents of this registry should be: [[RFC Editor: Replace xxxx below with the number of this RFC.]] Decimal Meaning Reference ------- ------- --------- 0 RESERVED. RFC XXXX 1...2147483647 AVAILABLE for registration. 2147483648 RESERVED. RFC XXXX IANA will register new values on a First Come First Served basis, as defined in BCP 64 [2]. Changing the RESERVED values (0 and 2147483648) will require IETF Consensus. While the registration procedures do not require expert review, authors of expansion are encouraged to seek community review and comment whenever that is feasible. Authors may seek community review by posting a specification of their proposed mechanism as an Internet-Draft. Expansions intended for widespread use should be Josefsson Expires May 16, 2006 [Page 4]
Internet-Draft Kerberos 5 TCP/IP Expansion Mechanism November 2005 standardized through the normal IETF process, when appropriate. 6. Copying conditions The author grants third parties the irrevocable right to copy, use and distribute this document, with or without modification, in any medium, without royalty. The author requests that any citation or excerpt of unmodified text reference this document. If the text is modified in any way other than translation, any claim of endorsement by the IETF or status within its document series must be removed. 7. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. [3] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The Kerberos Network Authentication Service (V5)", RFC 4120, July 2005. Josefsson Expires May 16, 2006 [Page 5]
Internet-Draft Kerberos 5 TCP/IP Expansion Mechanism November 2005 Author's Address Simon Josefsson Email: simon@josefsson.org Josefsson Expires May 16, 2006 [Page 6]
Internet-Draft Kerberos 5 TCP/IP Expansion Mechanism November 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2005). 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. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Josefsson Expires May 16, 2006 [Page 7]
