Network Working Group                                   A. Melnikov, Ed.
Internet-Draft                                                 Isode Ltd
Updates: 5802, 7677 (if approved)                           11 July 2022
Intended status: Standards Track
Expires: 12 January 2023


Salted Challenge Response Authentication Mechanism (SCRAM) SASL and GSS-
                             API Mechanisms
                      draft-melnikov-scram-bis-01

Abstract

   This document updates requirements on implementations of various
   Salted Challenge Response Authentication Mechanism (SCRAM) Simple
   Authentication and Security Layer (SASL) mechanisms based on more
   modern security practices.

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 https://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 12 January 2023.

Copyright Notice

   Copyright (c) 2022 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 (https://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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.



Melnikov                 Expires 12 January 2023                [Page 1]


Internet-Draft                 SASL SCRAM                      July 2022


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Key Word Definitions  . . . . . . . . . . . . . . . . . . . .   2
   3.  Implementation Recommendations  . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   The intent of this document is to serve as an implementor's roadmap
   for implementing various Salted Challenge Response Authentication
   Mechanism (SCRAM) [RFC5802] SASL [RFC4422] mechanisms.

   [RFC5802] defined the generic SCRAM framework and described
   instantiation of a SCRAM mechanism using SHA-1 hash function: SCRAM-
   SHA-1 (and SCRAM-SHA-1-PLUS).  [RFC7677] described another
   instantiation using SHA-256 hash function (SCRAM-SHA-256 and SCRAM-
   SHA-256-PLUS) and also clarified conditions for using the mandatory-
   to-implement "tls-unique" channel binding with TLS 1.2.
   [tls-1.3-channel-binding] defines the "tls-exporter" channel binding
   that is to be used when a SCRAM mechanism is used over TLS 1.3
   [RFC8446] or later.

   [I-D.melnikov-scram-sha-512] and [I-D.melnikov-scram-sha3-512] define
   further instantiations of SCRAM using SHA-512 and SHA3-512 hash
   functions respectively.

   [I-D.melnikov-scram-2fa] defines an extension to SCRAM for two factor
   authentication.  It is applicable to all instantiations of SCRAM.

2.  Key Word Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all









Melnikov                 Expires 12 January 2023                [Page 2]


Internet-Draft                 SASL SCRAM                      July 2022


3.  Implementation Recommendations

   [tls-1.3-channel-binding] document updated [RFC5802] and [RFC7677] to
   use the "tls-exporter" channel binding as the mandatory to implement
   (instead of "tls-unique") when a SCRAM mechanism is used over TLS 1.3
   [RFC8446] or later.

   [[Discuss if rough consensus can be reached on this in the KITTEN
   WG.]] All SCRAM implementations SHOULD support
   [I-D.melnikov-scram-2fa] to allow for two factor authentication with
   SCRAM.

   [[Possibly narrow down choices to only one of these.  Discuss in the
   KITTEN WG.]] Unless required for backward compatibility, server and
   client implementations MUST support SCRAM-SHA-512-PLUS/SCRAM-SHA-512
   [I-D.melnikov-scram-sha-512] and/or SCRAM-SHA3-512-PLUS/SCRAM-
   SHA3-512 [I-D.melnikov-scram-sha3-512] instead of SCRAM-SHA-1-PLUS/
   SCRAM-SHA-1 [RFC5802].

   [RFC5803] describes how SCRAM hashes can be stored in LDAP.  It is
   compatible with all versions of SCRAM described in this document,
   including SCRAM-SHA-256, SCRAM-SHA-512 and SCRAM-SHA3-512.

4.  Security Considerations

   The security considerations from [RFC5802] still apply.

   To be secure, SCRAM-*-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.  When using SCRAM over TLS 1.2
   [RFC5246], the "tls-unique" channel binding is still the default
   channel binding to use (see Section 6.1 of [RFC5802]), assuming the
   above conditions are satisfied.  When using SCRAM over TLS 1.3
   [RFC8446], the "tls-exporter" channel binding
   [tls-1.3-channel-binding] is the default (in the sense specified in
   Section 6.1 of [RFC5802]) to use.

   See [RFC4270] and [RFC6194] for reasons to move from SHA-1 to a
   strong security mechanism like SHA-512.

   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 10000 takes around 0.5 seconds on current mobile handsets.



Melnikov                 Expires 12 January 2023                [Page 3]


Internet-Draft                 SASL SCRAM                      July 2022


   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 10000, but careful consideration ought to be
   given to using a significantly higher value, particularly where
   mobile use is less important.

5.  IANA Considerations

   IANA is requested to add RFC XXXX as an extra reference for the
   following SASL SCRAM mechanisms listed in the "SASL SCRAM Family
   Mechanisms" registry: SCRAM-SHA-1, SCRAM-SHA-1-PLUS, SCRAM-SHA-256
   and SCRAM-SHA-256-PLUS.

6.  References

6.1.  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,
              <https://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,
              <https://www.rfc-editor.org/info/rfc4422>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [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,
              <https://www.rfc-editor.org/info/rfc5802>.

   [RFC5803]  Melnikov, A., "Lightweight Directory Access Protocol
              (LDAP) Schema for Storing Salted Challenge Response
              Authentication Mechanism (SCRAM) Secrets", RFC 5803,
              DOI 10.17487/RFC5803, July 2010,
              <https://www.rfc-editor.org/info/rfc5803>.







Melnikov                 Expires 12 January 2023                [Page 4]


Internet-Draft                 SASL SCRAM                      July 2022


   [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,
              <https://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,
              <https://www.rfc-editor.org/info/rfc7627>.

   [RFC7677]  Hansen, T., "SCRAM-SHA-256 and SCRAM-SHA-256-PLUS Simple
              Authentication and Security Layer (SASL) Mechanisms",
              RFC 7677, DOI 10.17487/RFC7677, November 2015,
              <https://www.rfc-editor.org/info/rfc7677>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [tls-1.3-channel-binding]
              Whited, S., "Channel Bindings for TLS 1.3", Work in
              Progress, Internet-Draft, draft-ietf-kitten-tls-channel-
              bindings-for-tls13-11, 18 October 2021,
              <https://www.ietf.org/archive/id/draft-ietf-kitten-tls-
              channel-bindings-for-tls13-11.txt>.

   [I-D.melnikov-scram-2fa]
              Melnikov, A., "Extensions to Salted Challenge Response
              (SCRAM) for 2 factor authentication", Work in Progress,
              Internet-Draft, draft-melnikov-scram-2fa-03, 24 May 2021,
              <https://www.ietf.org/archive/id/draft-melnikov-scram-2fa-
              03.txt>.

   [I-D.melnikov-scram-sha-512]
              Melnikov, A., "SCRAM-SHA-512 and SCRAM-SHA-512-PLUS Simple
              Authentication and Security Layer (SASL) Mechanisms", Work
              in Progress, Internet-Draft, draft-melnikov-scram-sha-
              512-02, 19 October 2021, <https://www.ietf.org/internet-
              drafts/draft-melnikov-scram-sha-512-02.txt>.

   [I-D.melnikov-scram-sha3-512]
              Melnikov, A., "SCRAM-SHA3-512 and SCRAM-SHA3-512-PLUS
              Simple Authentication and Security Layer (SASL)



Melnikov                 Expires 12 January 2023                [Page 5]


Internet-Draft                 SASL SCRAM                      July 2022


              Mechanisms", Work in Progress, Internet-Draft, draft-
              melnikov-scram-sha3-512-02, 19 October 2021,
              <https://www.ietf.org/internet-drafts/draft-melnikov-
              scram-sha3-512-02.txt>.

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,
              <https://www.rfc-editor.org/info/rfc4270>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <https://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,
              <https://www.rfc-editor.org/info/rfc6194>.

Acknowledgements

   This document is based on RFC 7677 by Tony Hansen.

   Thank you to Ludovic Bocquet for comments and corrections.

Author's Address

   Alexey Melnikov (editor)
   Isode Ltd
   14 Castle Mews
   Hampton
   TW12 2NP
   United Kingdom
   Email: alexey.melnikov@isode.com














Melnikov                 Expires 12 January 2023                [Page 6]