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Re: [kitten] WGLC on draft-ietf-kitten-aes-cts-hmac-sha2-06

Luke Howard <lukeh@padl.com> Wed, 15 April 2015 15:13 UTC

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From: Luke Howard <lukeh@padl.com>
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Date: Thu, 16 Apr 2015 01:13:26 +1000
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To: D.Rogers@gmx.net
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Cc: "kitten@ietf.org" <kitten@ietf.org>, "mjjenki@tycho.ncsc.mil" <mjjenki@tycho.ncsc.mil>
Subject: Re: [kitten] WGLC on draft-ietf-kitten-aes-cts-hmac-sha2-06
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> On 15 Apr 2015, at 7:54 pm, D.Rogers@gmx.net wrote:
> 
> Starting from a larger set and truncating to the same end result does improve security, it may reduce it.


My understanding is that as long as the hash function has strong diffusion this is not a problem. The different SHA-2 variants are all truncated versions of SHA-512 (with different initial values). Also, not relevant here (because HMAC is used) but truncating hashes can actually improve security by avoiding length extension attacks.

Feel free to correct me as I’m not a cryptographer, I don’t even play one on TV… :)

— Luke

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