linux-kernel - Re: [PATCH] lib: memcmp_nta: add timing-attack secure memcmp

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Date:	Mon, 11 Feb 2013 10:37:45 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Daniel Borkmann <dborkman@...hat.com>
CC:	gregkh@...uxfoundation.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib: memcmp_nta: add timing-attack secure memcmp

On 02/10/2013 02:00 PM, Daniel Borkmann wrote:
> If you need to compare a password or a hash value, the timing of the
> comparison function can give valuable clues to the attacker. Let's
> say the password is 123456 and the attacker tries abcdef. If the
> comparision function fails at the first byte without looking at the
> other bytes, then the attacker can measure the difference in runtime
> and deduce which byte was wrong, reducing the attack space from
> exponential to polynomial. [Daniel J. Bernstein]
> 
> Therefore add memcmp_nta ({n}o {t}iming {a}ttacks) in order to avoid
> such scenarios and to facilitate development by providing a generic
> function for (e.g.) the crypto and networking subsystems.
> 
> Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
> ---

I read this as "compare memory with non-temporal access".  Perhaps
something like "memcpy_constant_time" would be less confusing.

--Andy
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