linux-kernel - RE: [PATCH v5 1/4] siphash: add cryptographically secure PRF

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Date:   Mon, 19 Dec 2016 14:14:59 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'George Spelvin' <linux@...encehorizons.net>,
        "tom@...bertland.com" <tom@...bertland.com>
CC:     "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "djb@...yp.to" <djb@...yp.to>,
        "ebiggers3@...il.com" <ebiggers3@...il.com>,
        "hannes@...essinduktion.org" <hannes@...essinduktion.org>,
        "Jason@...c4.com" <Jason@...c4.com>,
        "jeanphilippe.aumasson@...il.com" <jeanphilippe.aumasson@...il.com>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "luto@...capital.net" <luto@...capital.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "tytso@....edu" <tytso@....edu>,
        "vegard.nossum@...il.com" <vegard.nossum@...il.com>
Subject: RE: [PATCH v5 1/4] siphash: add cryptographically secure PRF

From: George Spelvin
> Sent: 17 December 2016 15:21
...
> uint32_t
> hsiphash24(char const *in, size_t len, uint32_t const key[2])
> {
> 	uint32_t c = key[0];
> 	uint32_t d = key[1];
> 	uint32_t a =     0x6c796765 ^ 0x736f6d65;
> 	uint32_t b = d ^ 0x74656462 ^ 0x646f7261;

I've not looked closely, but is that (in some sense) duplicating
the key length?
So you could set a = key[2] and b = key[3] and still have an
working hash - albeit not exactly the one specified.

I'll add another comment here...
Is it worth using the 32bit hash for IP addresses on 64bit systems that
can't do misaligned accessed?

	David