Internet DRAFT - draft-hansen-scram-sha256
draft-hansen-scram-sha256
Kitten T. Hansen
Internet-Draft AT&T Laboratories
Updates: 5802 (if approved) August 25, 2015
Intended status: Standards Track
Expires: February 26, 2016
SCRAM-SHA-256 and SCRAM-SHA-256-PLUS SASL Mechanisms
draft-hansen-scram-sha256-04
Abstract
This document registers: the SASL mechanisms SCRAM-SHA-256 and SCRAM-
SHA-256-PLUS, provdes guidance for secure implentation of the
original SCRAM-SHA-1-PLUS mechanism, and 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.
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This Internet-Draft will expire on February 26, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Key Word Definitions . . . . . . . . . . . . . . . . . . . . 3
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 . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 7
7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 8
A.1. Changes for -03 to -04 . . . . . . . . . . . . . . . . . 8
A.2. Changes for -02 to -03 . . . . . . . . . . . . . . . . . 8
A.3. Changes for -01 to -02 . . . . . . . . . . . . . . . . . 8
A.4. 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].
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
[I-D.ietf-tls-session-hash]. 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.
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).
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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.
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.
To be secure, SCRAM-SHA-256-PLUS and SCRAM-SHA-1-PLUS MUST either be
used over a TLS channel that has had [I-D.ietf-tls-session-hash]
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-
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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.
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
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SASL mechanism name (or prefix for the family): SCRAM-<NAME>
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
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.
[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:
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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
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, Stephen Farrell, Simon Josefsson, Pearl Liang,
Alexey Melnikov, Peter Saint-Andre, Robert Sparks, Martin Thompson
and Nico Williams for their comments on this topic.
7. References
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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,
<http://www.rfc-editor.org/info/rfc4422>.
[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>.
[I-D.ietf-tls-session-hash]
Bhargavan, K., Delignat-Lavaud, A., Pironti, A., Langley,
A., and M. Ray, "Transport Layer Security (TLS) Session
Hash and Extended Master Secret Extension", draft-ietf-
tls-session-hash-06 (work in progress), July 2015.
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,
<http://www.rfc-editor.org/info/rfc2119>.
[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>.
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[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>.
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 -03 to -04
Added text to the Abstract, Introduction (Section 1), and Security
Considerations (Section 4) sections regarding tls-session-hash
negotiation.
A.2. 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.
A.3. Changes for -01 to -02
Removed !!!!!!!!!!!!!!!! comments requesting discussion after
discussion on kitten mailing list.
A.4. 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
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Tony Hansen
AT&T Laboratories
200 Laurel Ave. South
Middletown, NJ 07748
USA
Email: tony+scramsha256@maillennium.att.com
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