SASL Working Group A. Melnikov Internet-Draft Isode Limited Intended status: Standards Track July 30, 2009 Expires: January 31, 2010 LDAP schema for storing SCRAM secrets draft-melnikov-sasl-scram-ldap-02 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and 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 January 31, 2010. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. 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. Melnikov Expires January 31, 2010 [Page 1] Internet-Draft LDAP schema for storing SCRAM secrets July 2009 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. 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 Melnikov Expires January 31, 2010 [Page 2] Internet-Draft LDAP schema for storing SCRAM secrets July 2009 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 (always without the "-PLUS" suffix), e.g. "SCRAM- 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-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 authPassword attribute before using it for performing a SCRAM authentication exchange. It is Melnikov Expires January 31, 2010 [Page 3] Internet-Draft LDAP schema for storing SCRAM secrets July 2009 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. 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 January 31, 2010 [Page 4] Internet-Draft LDAP schema for storing SCRAM secrets July 2009 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 January 31, 2010 [Page 5]