linux-kernel - Re: [PATCH v0] Add SHA-3 hash algorithm

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Date:	Wed, 03 Oct 2012 02:53:27 -0400
From:	Jeff Garzik <jgarzik@...ox.com>
To:	David Miller <davem@...emloft.net>
CC:	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
	herbert@...dor.apana.org.au
Subject: Re: [PATCH v0] Add SHA-3 hash algorithm

On 10/03/2012 02:06 AM, David Miller wrote:
> From: Jeff Garzik <jeff@...zik.org>
> Date: Wed, 3 Oct 2012 01:45:42 -0400
>
>> 1) tcrypt setup blatantly wrong.  What is the best setup here?  Define a
>> separate entry for each digest length?  Is there some special string
>> descriptor format that is desired, like "sha3-256" or "sha3(256)"?
>
> Good question.  The base name should probably be something without
> dashes.  Maybe "sha3_256", but yeah "sha3256" would look rediculous.

Well, the more basic question was...  what to do when the digest length 
is easily variable, vis a vis kernel hash APIs?

Keccak message digest size may fall anywhere within the range 8 bits - 
1600 bits at runtime.  You choose the digest size when you init the 
context.  In contrast, the kernel interface appears to require a 
hardcoded size, chosen at driver compile time.

My patch picks sizes found in common use, consistent with existing 
kernel practice.  However, it is valid for another Keccak user to 
produce a 1600 bit hash, or a 1592 bit hash, or a 1584 bit hash, etc., etc.

Maybe my patch is the best we can do in the current kernel, if dynamic 
digest size is not currently possible. Register "sha3_224", "sha3_256", 
... as you describe, and wait for actual users to appear with 
unsupported digest sizes.

	Jeff

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