linux-kernel - Re: [PATCH v3 1/3] siphash: add cryptographically secure hashtable function

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Date:   Thu, 15 Dec 2016 00:17:18 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Tom Herbert <tom@...bertland.com>
Cc:     Netdev <netdev@...r.kernel.org>,
        kernel-hardening@...ts.openwall.com,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>,
        "Daniel J . Bernstein" <djb@...yp.to>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Eric Biggers <ebiggers3@...il.com>,
        David Laight <David.Laight@...lab.com>
Subject: Re: [PATCH v3 1/3] siphash: add cryptographically secure hashtable function

Hey Tom,

On Thu, Dec 15, 2016 at 12:14 AM, Tom Herbert <tom@...bertland.com> wrote:
> I'm confused, doesn't 2dword == 1qword? Anyway, I think the qword
> functions are good enough. If someone needs to hash over some odd
> length they can either put them in a structure padded to 64 bits or
> call the hash function that takes a byte length.

Yes. Here's an example:

static inline u64 siphash24_2dwords(const u32 a, const u32 b, const u8
key[SIPHASH24_KEY_LEN])
{
       return siphash24_1qword(((u64)b << 32) | a, key);
}

This winds up being extremely useful and syntactically convenient in a
few places. Check out my git branch in about 10 minutes or wait for v4
to be posted tomorrow; these are nice helpers.

> I'd still drop the "24" unless you really think we're going to have
> multiple variants coming into the kernel.

Okay. I don't have a problem with this, unless anybody has some reason
to the contrary.

Jason