linux-kernel - Re: [PATCH v3 7/8] crypto/sha3: Add SHAKE128/256 support

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Message-ID: <2284488.1759323746@warthog.procyon.org.uk>
Date: Wed, 01 Oct 2025 14:02:26 +0100
From: David Howells <dhowells@...hat.com>
To: Eric Biggers <ebiggers@...nel.org>
Cc: dhowells@...hat.com, "Jason A . Donenfeld" <Jason@...c4.com>,
    Ard Biesheuvel <ardb@...nel.org>,
    Herbert Xu <herbert@...dor.apana.org.au>,
    Stephan Mueller <smueller@...onox.de>, linux-crypto@...r.kernel.org,
    linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 7/8] crypto/sha3: Add SHAKE128/256 support

Eric Biggers <ebiggers@...nel.org> wrote:

> I recommend holding off on this part until you have a try at using the
> SHAKE library API directly.  The dispatch to different algorithms could
> be done in the calling code.  This patch would also limit the ML-DSA
> code to fixed-size SHAKE outputs; is that really going to be enough?

Actually, ML-DSA also allows SHA2 hashes for the prehash, so if I use
crypto_shash for that, then I maintain the flexibility through that.

> When there's only a small number of supported algorithms, just doing the
> dispatch in the calling code tends to be simpler than using
> crypto_shash.  For example, see the recent conversion of fs/verity/ to
> use the SHA-2 library API instead of crypto_shash.

That's reinventing the wheel.  Why have crypto_shash at all if we're going to
encourage people to ignore that and use a union and an enum/ops table.

Is the goal to get rid of crypto/ entirely and use lib/crypto/ instead?  Not
that I wouldn't mind a better crypto offloading API - the one we have kind of
sucks, especially for offloading to async crypto h/w (sorry Herbert;-)).

David