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

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Date:   Sat, 17 Dec 2016 02:39:50 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     George Spelvin <linux@...encehorizons.net>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        David Miller <davem@...emloft.net>,
        David Laight <David.Laight@...lab.com>,
        "Daniel J . Bernstein" <djb@...yp.to>,
        Eric Biggers <ebiggers3@...il.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>,
        kernel-hardening@...ts.openwall.com,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Netdev <netdev@...r.kernel.org>,
        Tom Herbert <tom@...bertland.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Theodore Ts'o" <tytso@....edu>,
        Vegard Nossum <vegard.nossum@...il.com>
Subject: Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF

On Sat, Dec 17, 2016 at 12:44 AM, George Spelvin
<linux@...encehorizons.net> wrote:
> Ths advice I'd give now is:
> - Implement
> unsigned long hsiphash(const void *data, size_t len, const unsigned long key[2])
>   .. as SipHash on 64-bit (maybe SipHash-1-3, still being discussed) and
>   HalfSipHash on 32-bit.

I already did this. Check my branch.

> - Document when it may or may not be used carefully.

Good idea. I'll write up some extensive documentation about all of
this, detailing use cases and our various conclusions.

> - #define get_random_int (unsigned)get_random_long

That's a good idea, since ultimately the other just casts in the
return value. I wonder if this could also lead to a similar aliasing
with arch_get_random_int, since I'm pretty sure all rdrand-like
instructions return native word size anyway.

> - Ted, Andy Lutorminski and I will try to figure out a construction of
>   get_random_long() that we all like.

And me, I hope... No need to make this exclusive.

Jason