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Date:	Sun, 07 Dec 2014 14:41:36 +0100
From:	Hannes Frederic Sowa <>
To:	George Spelvin <>
Subject: Re: Where exactly will arch_fast_hash be used

On So, 2014-12-07 at 08:30 -0500, George Spelvin wrote:
> Thanks for the encouragement!
> > Please consider xfs, too.
> > AFAIK xfs doesn't seed their hashing so far and the hashing function is
> > pretty weak. One example:
> >
> Is that something that *can* be changed without breaking the
> disk format?  SipHash is explicitly *not* designed to be secure as
> an unkeyed hash in the way that SHA-type algorithms are.

I did some research and it looked like it would need a change to the
disk format but it should be doable by incrementing the super block
version, so at least newly created filesystem would benefit from it.

> What it's designed to do is provide second preimage resistance
> of its output, or a function (like modular reduction) of its output,
> against an attacker who doesn't know the secret seed.
> > Ack. If we want to use it in the networking stack we should be able to
> > use it without a dependency to the crypto framework.
> Already understood.  My big question is whether a single function call
> is okay or we need something inlinable.

Like md5_transfrom, I think a non-inline function would be just fine.
Otherwise kernel code size would increase. Most hash users in the
network stack mostly deal with less bytes of input than one round needs.


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