Subject: [Ietf-krb-wg] Hash algorithm support in draft-ietf-krb-wg-otp-preauth

From: <[email-masked]>
Date: Fri, 7 Oct 2011 12:07:49 -0400

Currently, the OTP pre-auth draft has SHA1 as mandatory to implement:

      supportedHashAlg
         If present then a hash of the OTP value MUST be used in the key
         derivation rather than the plain text value.  Each
         AlgorithmIdentifier identifies a hash algorithm that is
         supported by the KDC in decreasing order of preference.  The
         client MUST select the first algorithm from the list that it
         supports.  Support for SHA1 by both the client and KDC is
         REQUIRED.  The AlgorithmIdentifier selected by the client MUST
         be placed in the hashAlg element of the PA-OTP-REQUEST.

In a comment in his recent review, Sean Turner asked if this could be changed to SHA-256.

I went back through WG discussions and the SHA1 requirement seems to stem from the fact that AES256-CTS-HMAC-SHA1-96 is required and so SHA1 will be available.

Before I reply to Sean, I just wanted to check if people think we should stick with SHA1 or if it is safe to change to SHA256.

--Gareth

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From: Greg Hudson <[email-masked]>
Date: Fri, 07 Oct 2011 18:22:55 -0400

On Fri, 2011-10-07 at 12:07 -0400, [email-masked] wrote:
> Before I reply to Sean, I just wanted to check if people think we
> should stick with SHA1 or if it is safe to change to SHA256.

draft-ietf-krb-wg-pkinit-alg-agility-04 makes a KDF based on SHA-256
support mandatory to implement ("Implementations comforming to this
specification MUST support id-pkinit-kdf-ah-sha256.").  So I think
SHA-256 is already in the family, and we don't have a strong argument to
sticking to SHA-1 as mandatory-to-implement for a new standard.

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From: <[email-masked]>
Date: Mon, 10 Oct 2011 06:37:54 -0400

> sticking to SHA-1 as mandatory-to-implement for a new standard.

OK, I'll make SHA-256 mandatory-to-implement then.