Internet Draft T. Hansen draft-hansen-sasl-pki-00.txt AT&T Laboratories Valid for six months February 23, 2003 The PKI SASL Mechanism Authors' version: 1.2 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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 memo and its companions will hopefully be discussed on the SASL working group mailing list, ietf-sasl@imc.org. To subscribe, send a message with the word "subscribe" in the body (on a line by itself) to the address ietf-sasl-request@imc.org. An archive of the mailing list may be found at http://www.ietf.org/archive/sasl. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract This document defines a user/password Simple Authentication and Security Layer(SASL) mechanism called the PKI mechanism. The PKI mechanism is intended to be used in situations where (1) passwords must be encrypted, (2) the password must be recoverable, and (3) using TLS in Hansen [Page 1] Internet Draft February 23, 2003 combination with a SASL mechanism such as PLAIN is inappropriate. NOTE: This document is a straw proposal to see what interest there is in having a SASL mechanism such as this. See the first section below for more information on why this mechanism is needed. 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 [RFC-KEYWORDS]. 1. Background and Intended Usage Clear-text passwords are simple, interoperate with almost all existing operating system authentication databases, and are useful for a smooth transition to a more secure password-based authentication mechan- ism. The drawback is that they are unacceptable for use over an unen- crypted network connection. Examples of clear-text password SASL mechanisms are PLAIN and LOGIN. All of the existing SASL mechanisms (other than PLAIN and LOGIN) perform their password validation by trading information derived from the username and password, combined in various ways with other informa- tion. Examples of such mechanisms are DIGEST, OTP and GSSAPI. There exists a class of servers that do their authentication by making use of a third party server, such as a RADIUS server. In order to do this, these servers must have the actual password in hand in order to pass on the appropriate information to the third party server. To do this, these servers currently must either (1) use a clear-text password, or (2) start a TLS session before authenticating using a clear-text password mechanism. Obviously, the first choice is not acceptable. Unfortunately, the second choice presents a considerable amount of con- tinuing overhead for the remainder of the session. The TLS session could be switched over to a null cipher, after SASL authentication has been performed. However, the TLS session still would have overheads associated with it that may not be acceptable to the outer protocol. This document defines the PKI Simple Authentication and Security Layer ([SASL]) mechanism for use in protocols where (1) passwords must be encrypted, (2) the password must be recoverable, and (3) using TLS in combination with a SASL mechanism such as PLAIN is inappropriate. The name associated with this mechanism is "PKI". The PKI SASL mechanism does not provide a security layer. This mechanism SHOULD NOT be used without adequate security protection as the Hansen [Page 2] Internet Draft February 23, 2003 mechanism affords no integrity nor confidentiality protection itself. 2. PKI SASL mechanism NOTE: NOTE: NOTE: The following is strictly a straw proposal to get the ball rolling. It has not been vetted by any sort of security review. Nor is the following description yet a formal description. It is probable that my description of TLS has flaws, and there is clearly room for improvement all around. It is clear that invoking TLS, and then passing the password over the subsequent encrypted channel is considered safe by today's stan- dards. The intent is that the PKI SASL mechanism would be equally secure to this. With TLS, the first step in the protocol is to exchange Public Key credentials. Session keys are then established, using a Diffie-Helman exchange encrypted using the public key. The remainder of the session is then encrypted, using a symmetric encryption algorithm and the ses- sion key as the encryption key. With the PKI SASL mechanism, the first step in the protocol is to transmit the server Public Key credentials. Session keys are then esta- blished, using a Diffie-Helman exchange encrypted using the public key. The last step is to transmit to the server an authorization identity (the identity to log in as), authentication identity (the identity whose password will be used), and a password. These are separated by NUL characters and encrypted using a symmetric encryption algorithm and the session key as the encryption key. NOTE: It is intended that the authorization identity, authenticia- tion identity and password are to be processed in a way comparable to what is used in draft-ietf-sasl-plain-*.txt. FORMAL DESCRIPTION WOULD FOLLOW 3. Example An example of this mechanism would go here. 4. Security Considerations The PKI SASL mechanism is intended to be comparable in security to the use of the PLAIN SASL mechanism within a TLS encryption layer. As with the PLAIN mechanism, the server gains the ability to imper- sonate the user to all services with the same password regardless of any encryption provided by TLS or other network privacy mechanisms. While many other authentication mechanisms have similar weaknesses, stronger Hansen [Page 3] Internet Draft February 23, 2003 SASL mechanisms such as the Kerberos-based GSSAPI mechanism address this issue. Clients are encouraged to have an operational mode where all mechanisms which are likely to reveal the user's password to the server are disabled. It is RECOMMENDED that this mode be the default. General SASL security considerations apply to this mechanism. "stringprep" and Unicode security considerations also apply. 5. IANA Considerations It is requested that the SASL Mechanism registry [IANA-SASL] entry for the PKI mechanism be created, reflecting that this document provides its technical specification. To: iana@iana.org Subject: Updated Registration of SASL mechanism PLAIN SASL mechanism name: PKI Security considerations: See RFC XXXX. Published specification (optional, recommended): RFC XXXX Person & email address to contact for further information: Tony Hansen Intended usage: COMMON Author/Change controller: IESG 6. Acknowledgements TBD 7. Normative References [ABNF] D. Crocker, P. Overell, "Augmented BNF for Syntax Specifica- tions: ABNF", RFC 2234, November 1997. [Keywords] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14 (also RFC 2119), March 1997. [SASL] J. Myers, "Simple Authentication and Security Layer (SASL)", RFC 2222bis (a work in progress). [SASLPrep] TBD, "SASL String Preparation Profiles", (a work to come). [Stringprep] P. Hoffman, M. Blanchet, "Preparation of Internation- alized Strings ("stringprep")", RFC 3454, December 2002. [Unicode] The Unicode Consortium, "The Unicode Standard, Version 3.2.0", defined by: The Unicode Standard, Version 3.0 (Reading, MA, Addison-Wesley, 2000. ISBN 0-201-61633-5), as amended by the Unicode Hansen [Page 4] Internet Draft February 23, 2003 Standard Annex #28: Unicode 3.2 (http://www.unicode.org/reports/tr28/tr28-3.html). [UTF-8] F. Yergeau, "UTF-8, a transformation format of ISO 10646", RFC 2279, January 1998. [TLS] T. Dierks, C. Allen, "The TLS Protocol Version 1.0", RFC 2246, January 1999. 8. Informative References [CRAM-MD5] J. Klensin, R. Catoe, and P. Krumviede, "IMAP/POP AUTHorize Extension for Simple Challenge/Response", RFC 2195, September 1997. [DIGEST-MD5] P. Leach, C. Newman, "Using Digest Authentication as a SASL Mechanism", RFC 2831, May 2000. [IANA-SASL] IANA, "SIMPLE AUTHENTICATION AND SECURITY LAYER (SASL) MECHANISMS", http://www.iana.org/assignments/sasl-mechanisms. 9. Author's Address' Tony Hansen AT&T Laboratories Middletown, NJ 07748 USA Phone: +1.732.420.8934 Email: tony@att.com 10. Full Copyright Statement Copyright 2003, The Internet Society. All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and dis- tributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Stan- dards process must be followed, or as required to translate it into languages other than English. Hansen [Page 5] Internet Draft February 23, 2003 The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE AUTHORS, THE INTERNET SOCIETY, AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMA- TION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. This document expires August 23, 2003. Hansen [Page 6]