SCRAM-SHA-512 and SCRAM-SHA-512-PLUS Simple Authentication and Security Layer (SASL) Mechanisms
draft-melnikov-scram-sha-512-00

Abstract

This document registers the Simple Authentication and Security Layer (SASL) mechanisms SCRAM-SHA-512 and SCRAM-SHA-512-PLUS.

Status of This Memo

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Table of Contents

• 1. Introduction
• 2. Key Word Definitions
• 3. SCRAM-SHA-512 and SCRAM-SHA-512-PLUS
• 4. Security Considerations
• 5. IANA Considerations
• 6. References
• 6.1. Normative References
• 6.2. Informative References
• Acknowledgements
• Author's Address

1. Introduction

This document registers the SASL [RFC4422] mechanisms SCRAM-SHA-512 and SCRAM-SHA-512-PLUS. SHA-512 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.

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

3. SCRAM-SHA-512 and SCRAM-SHA-512-PLUS

The SCRAM-SHA-512 and SCRAM-SHA-512-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-512 instead of SHA-1 [RFC6234].

For the SCRAM-SHA-512 and SCRAM-SHA-512-PLUS SASL mechanisms, the hash iteration-count announced by a server SHOULD be at least 4096.

The GSS-API mechanism OID for SCRAM-SHA-512 is 1.3.6.1.5.5.<TBD> (see Section 5).

This is a simple example of a SCRAM-SHA-512 authentication exchange when the client doesn't support channel bindings. The username 'user' and password 'pencil' are being used.

4. Security Considerations

The security considerations from [RFC5802] still apply.

To be secure, either SCRAM-SHA-512-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-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 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.

5. IANA Considerations

IANA is requested to add the following new SASL SCRAM mechanisms to the "SASL SCRAM Family Mechanisms" registry:

• To:

  iana@iana.org

  Subject:

  Registration of a new SASL SCRAM Family mechanism SCRAM-SHA-512

  SASL mechanism name (or prefix for the family):

  SCRAM-SHA-512

  Security considerations:

  Section 4 of RFC XXXX

  Published specification (optional, recommended):

  RFC XXXX

  Minimum iteration-count:

  4096

  OID:

  1.3.6.1.5.5.<TBD>

  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-512-PLUS

  SASL mechanism name (or prefix for the family):

  SCRAM-SHA-512-PLUS

  Security considerations:

  Section 4 of RFC XXXX

  Published specification (optional, recommended):

  RFC XXXX

  Minimum iteration-count:

  4096

  OID:

  1.3.6.1.5.5.<TBD>

  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. References

6.1. Normative References

6.2. Informative References

Acknowledgements

This document is based on RFC 7677 by Tony Hansen.

Author's Address