linux-kernel - Re: [PATCH v2 3/4] secure_seq: use siphash24 instead of md5

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Message-ID: <CAHmME9qtRC5daEPgDEtNgP9tEajd=xRG=qkHE5XoOMA_zAeysw@mail.gmail.com>
Date:   Wed, 14 Dec 2016 22:01:29 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Tom Herbert <tom@...bertland.com>
Cc:     David Laight <David.Laight@...lab.com>,
        Netdev <netdev@...r.kernel.org>,
        kernel-hardening@...ts.openwall.com,
        Andi Kleen <ak@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>
Subject: Re: [PATCH v2 3/4] secure_seq: use siphash24 instead of md5_transform

On Wed, Dec 14, 2016 at 9:12 PM, Tom Herbert <tom@...bertland.com> wrote:
> If you pad the data structure to 64 bits then we can call the version
> of siphash that only deals in 64 bit words. Writing a zero in the
> padding will be cheaper than dealing with odd lengths in siphash24.
On Wed, Dec 14, 2016 at 9:27 PM, Hannes Frederic Sowa
<hannes@...essinduktion.org> wrote:
> What I don't really understand is that the addition of this complexity
> actually reduces the performance, as you have to take the "if (left)"
> branch during hashing and causes you to make a load_unaligned_zeropad.

Oh, duh, you guys are right. Fixed in my repo [1]. I'll submit the
next version in a day or so to let some other comments come in.

Thanks again for your reviews.

Jason

[1] https://git.zx2c4.com/linux-dev/log/?h=siphash