SASL Working Group A. Melnikov Internet-Draft Isode Limited Intended status: Standards Track November 19, 2008 Expires: May 23, 2009 LDAP schema for storing SCRAM secrets draft-melnikov-sasl-scram-ldap-01 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 23, 2009. Abstract This memo describes how authPassword LDAP attribute can be used 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 May 23, 2009 [Page 1] Internet-Draft LDAP schema for storing SCRAM secrets November 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 May 23, 2009 [Page 2] Internet-Draft LDAP schema for storing SCRAM secrets November 2008 1. Overview This memo defines a family of schema for authPassword attribute defined in [AUTHPASS]. Non terminal references in the following ABNF are defined in either [AUTHPASS] or [RFC5234]. The "scheme" part of the authPassword attribute is the SCRAM mechanism name, e.g. "SCRAM-HMAC-SHA-1". See [SCRAM] for the exact syntax of SCRAM mechanism names. The "authInfo" part of the authPassword attribute is the iteration count, followed by ":" and base-64 [BASE64] encoded salt. The "authValue" part of the authPassword attribute is the base-64 [BASE64] encoded StoredKey [SCRAM], followed by ":" and base-64 [BASE64] encoded ServerKey [SCRAM]. Syntax of the attribute can be expressed using ABNF [RFC5234]: scram-mech = "SCRAM-HMAC-SHA-1" ;; Complies with ABNF for scram-authInfo = iter-count ":" salt ;; Complies with ABNF for scram-authValue = stored-key ":" server-key ;; Complies with ABNF for iter-count = %x31-39 *DIGIT ; a positive number without leading zeros salt = <> stored-key = <> server-key = <> [[anchor2: Add an example.]] Note that the authPassword 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 using it for performing a SCRAM authentication exchange. It is possible that an attacker compromised the LDAP server or got access Melnikov Expires May 23, 2009 [Page 3] Internet-Draft LDAP schema for storing SCRAM secrets November 2008 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. [[anchor3: TBD.]] 3. IANA Considerations No action is required from IANA. 4. Acknowledgements The author gratefully acknowledges the feedback provided by Chris Newman and Kurt Zeilenga. 5. References 5.1. Normative References [AUTHPASS] Zeilenga, K., "LDAP Authentication Password Schema", RFC 3112, May 2001. [BASE64] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, October 2006. [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 May 23, 2009 [Page 4] Internet-Draft LDAP schema for storing SCRAM secrets November 2008 Author's Address Alexey Melnikov Isode Limited 5 Castle Business Village 36 Station Road Hampton, Middlesex TW12 2BX UK Email: alexey.melnikov@isode.com URI: http://www.melnikov.ca/ Melnikov Expires May 23, 2009 [Page 5] Internet-Draft LDAP schema for storing SCRAM secrets November 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. 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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 May 23, 2009 [Page 6]