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Internet Engineering Task Force (IETF)                         T. HansenRequest for Comments: 7677                             AT&T LaboratoriesUpdates:5802                                              November 2015Category: Standards TrackISSN: 2070-1721SCRAM-SHA-256 and SCRAM-SHA-256-PLUSSimple Authentication and Security Layer (SASL) MechanismsAbstract   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 ofRFC 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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://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 toBCP 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 2015Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .22.  Key Word Definitions  . . . . . . . . . . . . . . . . . . . .23.  SCRAM-SHA-256 and SCRAM-SHA-256-PLUS  . . . . . . . . . . . .24.  Security Considerations . . . . . . . . . . . . . . . . . . .35.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .45.1.  Updates to SCRAM-* Registration . . . . . . . . . . . . .45.2.  SASL-SCRAM Family Mechanisms Registration Procedure . . .46.  References  . . . . . . . . . . . . . . . . . . . . . . . . .66.1.  Normative References  . . . . . . . . . . . . . . . . . .66.2.  Informative References  . . . . . . . . . . . . . . . . .7   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .7   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .81.  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 (seeSection 5).   This is a simple example of a SCRAM-SHA-256 authentication exchange   when the client doesn't support channel bindings.  The username   'user' and password 'pencil' are being used.   C: n,,n=user,r=rOprNGfwEbeRWgbNEkqO   S: r=rOprNGfwEbeRWgbNEkqO%hvYDpWUa2RaTCAfuxFIlj)hNlF$k0,      s=W22ZaJ0SNY7soEsUEjb6gQ==,i=4096   C: c=biws,r=rOprNGfwEbeRWgbNEkqO%hvYDpWUa2RaTCAfuxFIlj)hNlF$k0,      p=dHzbZapWIk4jUhN+Ute9ytag9zjfMHgsqmmiz7AndVQ=   S: v=6rriTRBi23WpRR/wtup+mMhUZUn/dB5nLTJRsjl95G4=4.  Security Considerations   The security considerations from [RFC5802] still apply.   To be secure, either SCRAM-SHA-256-PLUS and SCRAM-SHA-1-PLUS MUST be   used over a TLS channel that has had the session hash extension   [RFC7627] negotiated, or session resumption MUST NOT have been used.   See [RFC4270] and [RFC6194] for reasons to move from SHA-1 to a   strong security mechanism like SHA-256.   The strength of this mechanism is dependent in part on the hash   iteration-count, as denoted by "i" in [RFC5802].  As a rule of thumb,   the hash iteration-count should be such that a modern machine will   take 0.1 seconds to perform the complete algorithm; however, this is   unlikely to be practical on mobile devices and other relatively low-   performance systems.  At the time this was written, the rule of thumb   gives around 15,000 iterations required; however, a hash iteration-   count of 4096 takes around 0.5 seconds on current mobile handsets.   This computational cost can be avoided by caching the ClientKey   (assuming the Salt and hash iteration-count is stable).  Therefore,   the recommendation of this specification is that the hash iteration-   count SHOULD be at least 4096, but careful consideration ought to be   given to using a significantly higher value, particularly where   mobile use is less important.Hansen                       Standards Track                    [Page 3]

RFC 7677          SASL SCRAM-SHA-256/SCRAM-SHA-256-PLUS    November 20155.  IANA Considerations5.1.  Updates to SCRAM-* Registration   The IANA registry for SCRAM-* (the SCRAM family of SASL mechanisms)   in the SASL mechanism registry ([RFC4422]) has been updated as   follows.  The email address for reviews has been updated, and the   note at the end changed.      To: iana@iana.org      Subject: Registration of a new SASL family SCRAM      SASL mechanism name (or prefix for the family): SCRAM-*      Security considerations:Section 7 of [RFC5802]      Published specification (optional, recommended):RFC 7677      Person & email address to contact for further information:         IETF KITTEN WG <kitten@ietf.org>      Intended usage: COMMON      Owner/Change controller: IESG <iesg@ietf.org>      Note: Members of this family MUST be explicitly registered using         the "IETF Review" [RFC5226] registration procedure.  Reviews         MUST be requested on the KITTEN mailing list kitten@ietf.org         (or a successor designated by the responsible Security AD).      Note to future SCRAM-mechanism designers: each new SASL SCRAM      mechanism MUST be explicitly registered with IANA within the SASL      SCRAM Family Mechanisms registry.5.2.  SASL-SCRAM Family Mechanisms Registration Procedure   A new IANA registry has been added for members of the SCRAM family of   SASL mechanisms, named "SASL SCRAM Family Mechanisms".  It adds two   new fields to the existing SCRAM mechanism registry: Minimum   iteration-count and Associated OID.  Below is the template for   registration of a new SASL family SCRAM.  (Note that the string   "TBD-BY-IANA" should be left as is, so that it may be filled in at   registration time by IANA.)Hansen                       Standards Track                    [Page 4]

RFC 7677          SASL SCRAM-SHA-256/SCRAM-SHA-256-PLUS    November 2015      To: iana@iana.org      Subject: Registration of a new SASL SCRAM family mechanism      SASL mechanism name (or prefix for the family): SCRAM-<NAME>      Security considerations:Section 7 of [RFC5802]      Published specification (optional, recommended):RFC 7677      Minimum iteration-count: The minimum hash iteration-count that         servers SHOULD announce      Associated OID: TBD-BY-IANA      Person & email address to contact for further information:         IETF KITTEN WG <kitten@ietf.org>      Intended usage: COMMON      Owner/Change controller: IESG <iesg@ietf.org>      Note: Members of this family MUST be explicitly registered using      the "IETF Review" [RFC5226] registration procedure.  Reviews MUST      be requested on the KITTEN mailing list kitten@ietf.org (or a      successor designated by the responsible Security Area Director).      Note: At publication of a new SASL SCRAM Family Mechanism, IANA      SHOULD assign a GSS-API mechanism OID for this mechanism from the      iso.org.dod.internet.security.mechanisms prefix (see the "SMI      Security for Mechanism Codes" registry) and fill in the value for      "TBD-BY-IANA" above.  Only one OID needs to be assigned for a      SCRAM-<NAME> and SCRAM-<NAME>-PLUS pair.  The same OID should be      assigned to both entries in the registry.      Note to future SASL SCRAM mechanism designers: each new SASL SCRAM      mechanism MUST be explicitly registered with IANA and MUST comply      with the SCRAM-mechanism naming convention defined inSection 4 of      [RFC5802].   The existing entries for SASL SCRAM-SHA-1 and SCRAM-SHA-1-PLUS have   been moved from the existing SASL mechanism registry to the "SASL   SCRAM Family Mechanisms" registry.  At that time, the following   values were added:      Minimum iteration-count: 4096      OID: 1.3.6.1.5.5.14 (from [RFC5802])Hansen                       Standards Track                    [Page 5]

RFC 7677          SASL SCRAM-SHA-256/SCRAM-SHA-256-PLUS    November 2015   The following new SASL SCRAM mechanisms have been added to the "SASL   SCRAM Family Mechanisms" registry:      To: iana@iana.org      Subject: Registration of a new SASL SCRAM Family mechanism         SCRAM-SHA-256      SASL mechanism name (or prefix for the family): SCRAM-SHA-256      Security considerations:Section 4 of RFC 7677      Published specification (optional, recommended):RFC 7677      Minimum iteration-count: 4096      OID: 1.3.6.1.5.5.18      Person & email address to contact for further information:         IETF KITTEN WG <kitten@ietf.org>      Intended usage: COMMON      Owner/Change controller: IESG <iesg@ietf.org>      Note:      To: iana@iana.org      Subject: Registration of a new SASL SCRAM Family mechanism         SCRAM-SHA-256-PLUS      SASL mechanism name (or prefix for the family): SCRAM-SHA-256-PLUS      Security considerations:Section 4 of RFC 7677      Published specification (optional, recommended):RFC 7677      Minimum iteration-count: 4096      OID: 1.3.6.1.5.5.18      Person & email address to contact for further information:         IETF KITTEN WG <kitten@ietf.org>      Intended usage: COMMON      Owner/Change controller: IESG <iesg@ietf.org>      Note:6.  References6.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <http://www.rfc-editor.org/info/rfc2119>.   [RFC4422]  Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple              Authentication and Security Layer (SASL)",RFC 4422,              DOI 10.17487/RFC4422, June 2006,              <http://www.rfc-editor.org/info/rfc4422>.Hansen                       Standards Track                    [Page 6]

RFC 7677          SASL SCRAM-SHA-256/SCRAM-SHA-256-PLUS    November 2015   [RFC5802]  Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams,              "Salted Challenge Response Authentication Mechanism              (SCRAM) SASL and GSS-API Mechanisms",RFC 5802,              DOI 10.17487/RFC5802, July 2010,              <http://www.rfc-editor.org/info/rfc5802>.   [RFC6234]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms              (SHA and SHA-based HMAC and HKDF)",RFC 6234,              DOI 10.17487/RFC6234, May 2011,              <http://www.rfc-editor.org/info/rfc6234>.   [RFC7627]  Bhargavan, K., Ed., Delignat-Lavaud, A., Pironti, A.,              Langley, A., and M. Ray, "Transport Layer Security (TLS)              Session Hash and Extended Master Secret Extension",RFC 7627, DOI 10.17487/RFC7627, September 2015,              <http://www.rfc-editor.org/info/rfc7627>.6.2.  Informative References   [RFC4270]  Hoffman, P. and B. Schneier, "Attacks on Cryptographic              Hashes in Internet Protocols",RFC 4270,              DOI 10.17487/RFC4270, November 2005,              <http://www.rfc-editor.org/info/rfc4270>.   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an              IANA Considerations Section in RFCs",BCP 26,RFC 5226,              DOI 10.17487/RFC5226, May 2008,              <http://www.rfc-editor.org/info/rfc5226>.   [RFC6194]  Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security              Considerations for the SHA-0 and SHA-1 Message-Digest              Algorithms",RFC 6194, DOI 10.17487/RFC6194, March 2011,              <http://www.rfc-editor.org/info/rfc6194>.   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security              (TLS) Protocol Version 1.2",RFC 5246,              DOI 10.17487/RFC5246, August 2008,              <http://www.rfc-editor.org/info/rfc5246>.Acknowledgements   This document benefited from discussions on the KITTEN WG mailing   list.  The author would like to specially thank Russ Allbery, Dave   Cridland, Shawn Emery, Stephen Farrell, Simon Josefsson, Pearl Liang,   Alexey Melnikov, Peter Saint-Andre, Robert Sparks, Martin Thompson,   and Nico Williams for their comments on this topic.Hansen                       Standards Track                    [Page 7]

RFC 7677          SASL SCRAM-SHA-256/SCRAM-SHA-256-PLUS    November 2015Author's Address   Tony Hansen   AT&T Laboratories   200 Laurel Ave. South   Middletown, NJ  07748   United States   Email: tony+scramsha256@maillennium.att.comHansen                       Standards Track                    [Page 8]