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
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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.
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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
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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 = <<base-64 encoded value>>
stored-key = <<base-64 encoded value>>
server-key = <<base-64 encoded value>>
[[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
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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.
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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/
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Full Copyright Statement
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