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Versions: 00 01 02 03 04 RFC 5803

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

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   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
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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.



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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




























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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 <scheme>

       scram-authInfo = iter-count ":" salt
                        ;; Complies with ABNF for <authInfo>

       scram-authValue = stored-key ":" server-key
                        ;; Complies with ABNF for <authValue>

       iter-count   = %x31-39 *DIGIT
                      ; a positive number without leading zeros

       salt         = <<base-64 encoded value>>

       stored-key   = <<base-64 encoded value>>

       server-key   = <<base-64 encoded value>>

   [[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



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   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.










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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/








































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