SCRAM-SHA-256 and SCRAM-SHA-256-PLUS Simple Authentication and Security Layer (SASL) Mechanisms
RFC 7677

Document Type RFC - Proposed Standard (November 2015; No errata)
Updates RFC 5802
Was draft-hansen-scram-sha256 (individual)
Last updated 2015-11-02
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Document shepherd Alexey Melnikov
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IESG IESG state RFC 7677 (Proposed Standard)
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Internet Engineering Task Force (IETF)                         T. Hansen
Request for Comments: 7677                             AT&T Laboratories
Updates: 5802                                              November 2015
Category: Standards Track
ISSN: 2070-1721

                  SCRAM-SHA-256 and SCRAM-SHA-256-PLUS
       Simple Authentication and Security Layer (SASL) Mechanisms

Abstract

   This document registers the Simple Authentication and Security Layer
   (SASL) mechanisms SCRAM-SHA-256 and SCRAM-SHA-256-PLUS, provides
   guidance for secure implementation of the original SCRAM-SHA-1-PLUS
   mechanism, and updates the SCRAM registration procedures of RFC 5802.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7677.

Copyright Notice

   Copyright (c) 2015 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Hansen                       Standards Track                    [Page 1]
RFC 7677          SASL SCRAM-SHA-256/SCRAM-SHA-256-PLUS    November 2015

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Key Word Definitions  . . . . . . . . . . . . . . . . . . . .   2
   3.  SCRAM-SHA-256 and SCRAM-SHA-256-PLUS  . . . . . . . . . . . .   2
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Updates to SCRAM-* Registration . . . . . . . . . . . . .   4
     5.2.  SASL-SCRAM Family Mechanisms Registration Procedure . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   This document registers the SASL mechanisms SCRAM-SHA-256 and SCRAM-
   SHA-256-PLUS.  SHA-256 has stronger security properties than SHA-1,
   and it is expected that SCRAM mechanisms based on it will have
   greater predicted longevity than the SCRAM mechanisms based on SHA-1.

   The registration form for the SCRAM family of algorithms is also
   updated from [RFC5802].

   After publication of [RFC5802], it was discovered that Transport
   Layer Security (TLS) [RFC5246] does not have the expected properties
   for the "tls-unique" channel binding to be secure [RFC7627].
   Therefore, this document contains normative text that applies to both
   the original SCRAM-SHA-1-PLUS and the newly introduced SCRAM-SHA-
   256-PLUS mechanism.

2.  Key Word Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3.  SCRAM-SHA-256 and SCRAM-SHA-256-PLUS

   The SCRAM-SHA-256 and SCRAM-SHA-256-PLUS SASL mechanisms are defined
   in the same way that SCRAM-SHA-1 and SCRAM-SHA-1-PLUS are defined in
   [RFC5802], except that the hash function for HMAC() and H() uses
   SHA-256 instead of SHA-1 [RFC6234].

   For the SCRAM-SHA-256 and SCRAM-SHA-256-PLUS SASL mechanisms, the
   hash iteration-count announced by a server SHOULD be at least 4096.

Hansen                       Standards Track                    [Page 2]
RFC 7677          SASL SCRAM-SHA-256/SCRAM-SHA-256-PLUS    November 2015

   The GSS-API mechanism OID for SCRAM-SHA-256 is 1.3.6.1.5.5.18 (see
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