SASL Working Group A. Melnikov Internet-Draft Isode Limited Intended status: Standards Track October 26, 2008 Expires: April 29, 2009 LDAP schema for storing SCRAM secrets draft-melnikov-sasl-scram-ldap-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 April 29, 2009. Abstract This memo describes LDAP schema for storing secrets used by Salted Challenge Response (SCRAM) Simple Authentication and Security Layer (SASL) Mechanism. Note A revised version of this draft document will be submitted to the RFC editor as a Proposed Standard for the Internet Community. Discussion and suggestions for improvement are requested, and should be sent to ietf-sasl@imc.org. Melnikov Expires April 29, 2009 [Page 1] Internet-Draft LDAP schema for storing SCRAM secrets October 2008 Table of Contents 1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Security Considerations . . . . . . . . . . . . . . . . . . . 3 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 5.1. Normative References . . . . . . . . . . . . . . . . . . . . 4 5.2. Informative References . . . . . . . . . . . . . . . . . . . 4 Author's Address . . . . . . . . . . . . . . . . . . . . . . 4 Intellectual Property and Copyright Statements . . . . . . . 6 Melnikov Expires April 29, 2009 [Page 2] Internet-Draft LDAP schema for storing SCRAM secrets October 2008 1. Overview ( [[OID TBD by IANA]] NAME 'saslSecretScram' DESC 'SCRAM mechanism secret' EQUALITY octetStringMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.40 ) The saslSecretScram attribute is a dollar ("$") separated octet string that contains information relevant for SCRAM [SCRAM] authentication. The syntax of the string is as follows: Hashing mechanism name, currently always "hmac-sha1". [[anchor2: Add a reference to the IANA registry.]] Iteration count. base-64 [[anchor3: Add reference]] encoded salt. base-64 [[anchor4: Add reference]] encoded StoredKey [SCRAM]. base-64 [[anchor5: Add reference]] encoded ServerKey [SCRAM]. Syntax of the attribute can be expressed using ABNF [RFC5234]: scram-secret = hash-mech "$" iter-count "$" salt "$" stored-key "$" server-key hash-mech = "hmac-sha1" iter-count = %x30-39 *DIGIT ; a positive number without leading zeros salt = <> stored-key = <> server-key = <> [[anchor6: Add an example.]] This attribute is multivalued. For example, it may contain multiple SCRAM hashes for different hashing algorithms. 2. Security Considerations Servers MUST validate format of the saslSecretScram attribute before Melnikov Expires April 29, 2009 [Page 3] Internet-Draft LDAP schema for storing SCRAM secrets October 2008 using it for performing a SCRAM authentication exchange. It is possible that an attacker compromised the LDAP server or got access to the entry containing the attribute in order to exploit a vulnerability in the subsystem performing SCRAM authentication exchange. Big iteration counts and invalid base-64 encoding are two possible (but not the only) exploits in the format specified in the document. [[anchor7: TBD.]] 3. IANA Considerations [[anchor8: TBD - assign OID for the new LDAP attribute.]] 4. Acknowledgements The author gratefully acknowledges the feedback provided by [[anchor10: XXX]]. 5. References 5.1. Normative References [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. [SCRAM] Menon-Sen, A. and C. Newman, "Salted Challenge Response (SCRAM) SASL Mechanism", draft-newman-auth-scram-07.txt (work in progress), July 2008. 5.2. Informative References [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and Security Layer (SASL)", RFC 4422, June 2006. Melnikov Expires April 29, 2009 [Page 4] Internet-Draft LDAP schema for storing SCRAM secrets October 2008 Author's Address Alexey Melnikov Isode Limited 5 Castle Business Village 36 Station Road Hampton, Middlesex TW12 2BX UK Email: am.gate.i@googlemail.com URI: http://www.melnikov.ca/ Melnikov Expires April 29, 2009 [Page 5] Internet-Draft LDAP schema for storing SCRAM secrets October 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). 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. 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, THE IETF TRUST 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. Intellectual Property 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. Melnikov Expires April 29, 2009 [Page 6]