Internet DRAFT - draft-melnikov-scram-bis
draft-melnikov-scram-bis
Network Working Group A. Melnikov, Ed.
Internet-Draft Isode Ltd
Updates: 5802, 7677 (if approved) 4 March 2024
Intended status: Standards Track
Expires: 5 September 2024
Salted Challenge Response Authentication Mechanism (SCRAM) SASL and GSS-
API Mechanisms
draft-melnikov-scram-bis-04
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
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 5 September 2024.
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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 . . . . . . . . . . . . . . . . . 5
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. [RFC9266]
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.kitten-scram-2fa] defines an extension to SCRAM for two factor
authentication. It is applicable to all instantiations of SCRAM with
different hash algorightms.
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
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3. Implementation Recommendations
[RFC9266] 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.kitten-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. The LDAP
format has a field for the hash algorithm name used, so 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 [RFC9266] 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.
This computational cost can be avoided by caching the ClientKey
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(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>.
[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>.
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[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>.
[RFC9266] Whited, S., "Channel Bindings for TLS 1.3", RFC 9266,
DOI 10.17487/RFC9266, July 2022,
<https://www.rfc-editor.org/info/rfc9266>.
[I-D.kitten-scram-2fa]
Melnikov, A., "Extensions to Salted Challenge Response
(SCRAM) for 2 factor authentication", Work in Progress,
Internet-Draft, draft-ietf-kitten-scram-2fa-04, 24 August
2023, <https://www.ietf.org/archive/id/draft-ietf-kitten-
scram-2fa-04.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-
512-04, 10 March 2022, <https://www.ietf.org/internet-
drafts/draft-melnikov-scram-sha-512-04.txt>.
[I-D.melnikov-scram-sha3-512]
Melnikov, A., "SCRAM-SHA3-512 and SCRAM-SHA3-512-PLUS
Simple Authentication and Security Layer (SASL)
Mechanisms", Work in Progress, Internet-Draft, draft-
melnikov-scram-sha3-512-04, 24 August 2023,
<https://www.ietf.org/internet-drafts/draft-melnikov-
scram-sha3-512-04.txt>.
6.2. Informative References
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[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
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