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

Viktor Dukhovni <viktor1dane@dukhovni.org> Wed, 15 April 2015 15:50 UTC

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Date: Wed, 15 Apr 2015 15:50:42 +0000
From: Viktor Dukhovni <viktor1dane@dukhovni.org>
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References: <alpine.GSO.1.10.1503301227280.22210@multics.mit.edu> <551D6C35.4080108@mit.edu> <alpine.GSO.1.10.1504081626110.22210@multics.mit.edu> <5525B044.8070509@mit.edu> <CAC2=hnfbLoRAQLwDQhL7pVYMS8kqfc1rAA6Ha1np1h1WnhT5aw@mail.gmail.com> <55271546.6020505@mit.edu> <597E759F-7941-4619-BCE0-DF604221EBB5@padl.com> <trinity-4f1ce1f7-6610-4a7e-aca8-c3205d929e2e-1429091657571@3capp-gmx-bs24> <46448841-4ABE-4176-88B1-94C2B26583C4@padl.com>
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Subject: Re: [kitten] WGLC on draft-ietf-kitten-aes-cts-hmac-sha2-06
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On Thu, Apr 16, 2015 at 01:13:26AM +1000, Luke Howard wrote:

> 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).

This is not the case.  There are algorithms SHA2-512 and SHA2-256
(either smaller internal state, fewer rounds or both).  SHA2-384
is a truncated SHA2-512 (with different initialization).  SHA2-224
is a truncated SHA2-256 (with different initialization).

-- 
	Viktor.