Kitten T. Hansen Internet-Draft AT&T Laboratories Updates: 5802 (if approved) July 20, 2015 Intended status: Standards Track Expires: January 21, 2016 SCRAM-SHA-256 and SCRAM-SHA-256-PLUS SASL Mechanisms draft-hansen-scram-sha256-03 Abstract This document registers the SASL mechanisms SCRAM-SHA-256 and SCRAM- SHA-256-PLUS. It also updates the SCRAM registration procedures of RFC 5802. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on January 21, 2016. 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 Expires January 21, 2016 [Page 1] Internet-Draft SASL SCRAM-SHA-256/SCRAM-SHA-256-PLUS July 2015 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Key Word Definitions . . . . . . . . . . . . . . . . . . . . 2 3. SCRAM-SHA-256 and SCRAM-SHA-256-PLUS . . . . . . . . . . . . 3 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. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.1. Normative References . . . . . . . . . . . . . . . . . . 6 7.2. Informative References . . . . . . . . . . . . . . . . . 7 7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 7 A.1. Changes for -02 to -03 . . . . . . . . . . . . . . . . . 7 A.2. Changes for -01 to -02 . . . . . . . . . . . . . . . . . 8 A.3. Changes for -00 to -01 . . . . . . . . . . . . . . . . . 8 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]. Note: this paragraph may be removed before publication. This document was written because [RFC5802] requires that new SASL mechanisms in the SCRAM family be subject to IETF review. This document is being discussed in the KITTEN working group (see the kitten@ietf.org [1] mailing list). It was pursued further because of a desire for its use within a document being discussed in the HTTP- AUTH working group (see the httpauth@ietf.org [2] mailing list). 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]. Hansen Expires January 21, 2016 [Page 2] Internet-Draft SASL SCRAM-SHA-256/SCRAM-SHA-256-PLUS July 2015 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. The GSS-API mechanism OID for SCRAM-SHA-256 is TBD1 (see Section 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. 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 an 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 iteration count is stable). Therefore the recommendation of this specification is that the 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 Expires January 21, 2016 [Page 3] Internet-Draft SASL SCRAM-SHA-256/SCRAM-SHA-256-PLUS July 2015 5. IANA Considerations 5.1. Updates to SCRAM-* Registration The IANA registry for SCRAM-* (the SCRAM family of SASL mechanisms) in the SASL Mechanism registry ([RFC4422]) is 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): RFCXXXX 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 is to be 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. To: iana@iana.org Subject: Registration of a new SASL SCRAM family mechanism SASL mechanism name (or prefix for the family): SCRAM- Security considerations: Section 7 of [RFC5802] Published specification (optional, recommended): RFCXXXX Minimum iteration-count: The minimum 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 Hansen Expires January 21, 2016 [Page 4] Internet-Draft SASL SCRAM-SHA-256/SCRAM-SHA-256-PLUS July 2015 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- and SCRAM--PLUS pair. The same OID should be assigned to both entries in the registry. [RFC Editor: This note should be removed before publication.] Note to IANA and the RFC Editor: The above string "TBD-BY-IANA" is NOT to be filled in with an OID within THIS document, but is to be placed as is within 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 in Section 4 of [RFC5802]. The existing entries for SASL SCRAM-SHA-1 and SCRAM-SHA-1-PLUS are to be moved from the existing SASL Mechanism registry to the SASL SCRAM Family Mechanism registry. When doing so, the following values are to be added: Minimum iteration-count: 4096 OID: 1.3.6.1.5.5.14 (from [RFC5802]) The following new SASL SCRAM mechanisms are added to the SASL SCRAM Family Mechanism registry: IANA has added the following entries to the SASL SCRAM Family Mechanism registry established by RFCXXXX: 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 Section 4 of RFCXXXX Published specification (optional, recommended): RFCXXXX Minimum iteration-count: 4096 OID: TBD1 Person & email address to contact for further information: IETF KITTEN WG kitten@ietf.org Hansen Expires January 21, 2016 [Page 5] Internet-Draft SASL SCRAM-SHA-256/SCRAM-SHA-256-PLUS July 2015 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 Section 4 of RFCXXXX Published specification (optional, recommended): RFCXXXX Minimum iteration-count: 4096 OID: "TBD1" 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: [This note may be removed on publication.] IANA needs to assign the GSS-API mechanism OID TBD1 listed above from the iso.org.dod.internet.security.mechanisms prefix (see the "SMI Security for Mechanism Codes" registry). 6. Acknowledgements This document benefited from discussions on the KITTEN WG mailing list. The author would like to specially thank Russ Albery, Dave Cridland, Shawn Emery, Simon Josefsson, Pearl Liang, Alexey Melnikov, Peter Saint-Andre, Martin Thompson and Nico Williams for their comments on this topic. 7. References 7.1. Normative References [RFC4422] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple Authentication and Security Layer (SASL)", RFC 4422, DOI 10.17487/RFC4422, June 2006, . [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, . Hansen Expires January 21, 2016 [Page 6] Internet-Draft SASL SCRAM-SHA-256/SCRAM-SHA-256-PLUS July 2015 [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, . 7.2. Informative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC4270] Hoffman, P. and B. Schneier, "Attacks on Cryptographic Hashes in Internet Protocols", RFC 4270, DOI 10.17487/RFC4270, November 2005, . [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, . [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, . 7.3. URIs [1] mailto:kitten@ietf.org [2] mailto:httpauth@ietf.org Appendix A. Change Log This section should be removed before publication as an RFC. A.1. Changes for -02 to -03 Changed from Informational document to Standards Track. Beefed up the Security Considerations (Section 4) section. At the request of IANA, reworked the IANA Considerations (Section 5) section. Hansen Expires January 21, 2016 [Page 7] Internet-Draft SASL SCRAM-SHA-256/SCRAM-SHA-256-PLUS July 2015 A.2. Changes for -01 to -02 Removed !!!!!!!!!!!!!!!! comments requesting discussion after discussion on kitten mailing list. A.3. Changes for -00 to -01 Added Security Considerations (Section 4) section. Added Minimum iteration-count and associated OID fields to registration forms and reworked the IANA Considerations (Section 5) section. Author's Address Tony Hansen AT&T Laboratories 200 Laurel Ave. South Middletown, NJ 07748 USA Email: tony+scramsha256@maillennium.att.com Hansen Expires January 21, 2016 [Page 8]