linux-kernel - Re: [PATCH v2] lib/crypto: Add SHA3-224, SHA3-256, SHA3-384, SHA-512, SHAKE128, SHAKE256

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Message-ID: <506171.1758637355@warthog.procyon.org.uk>
Date: Tue, 23 Sep 2025 15:22:35 +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>,
    Harald Freudenberger <freude@...ux.ibm.com>,
    Holger Dengler <dengler@...ux.ibm.com>,
    Herbert Xu <herbert@...dor.apana.org.au>,
    Stephan Mueller <smueller@...onox.de>, Simo Sorce <simo@...hat.com>,
    linux-crypto@...r.kernel.org, linux-s390@...r.kernel.org,
    keyrings@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] lib/crypto: Add SHA3-224, SHA3-256, SHA3-384, SHA-512, SHAKE128, SHAKE256

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

> Also, the parameter should be strongly typed: 'struct sha3_state *'
> Likewise in all the other functions that take the raw u64 array.

Those function may be directly substituted by calls to assembly code - so
u64[] is probably more appropriate.

> > +	for (round = 0; round < KECCAK_ROUNDS; round++) {
> > +		keccakf_round(st);
> > +		/* Iota */
> > +		st[0] ^= keccakf_rndc[round];
> > +	}
> 
> In the spec, "Iota" is part of the round.  Having it be separate from
> keccakf_round() in the code is confusing.

I assume that pertains to the comment about inlining in some way.  This is as
is in sha3_generic.c.  I can move it into the round function if you like, but
can you tell me what the effect will be?

> Second, the support for update() + squeeze() + update() + squeeze()
> seems to be trying to achieve something that is not defined in the SHA-3
> spec.  Could you elaborate on what it is meant to be doing, and why it's
> here?  According to the spec, the XOFs SHAKE128 and SHAKE256 actually
> just take a single message as their input.

Turns out I was misunderstanding what I was looking at whilst trying to adapt
Leancrypto's dilithium code.  Whilst it does squeeze a context several times,
it doesn't update it after finalising it without reinitialising it.

David