linux-kernel - Re: [PATCH v9 2/9] crypto: Add ML-DSA/Dilithium verify support

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Message-ID: <20251117171003.GC1584@sol>
Date: Mon, 17 Nov 2025 09:10:03 -0800
From: Eric Biggers <ebiggers@...nel.org>
To: David Howells <dhowells@...hat.com>
Cc: Herbert Xu <herbert@...dor.apana.org.au>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Petr Pavlu <petr.pavlu@...e.com>,
	Daniel Gomez <da.gomez@...nel.org>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	"Jason A . Donenfeld" <Jason@...c4.com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Stephan Mueller <smueller@...onox.de>,
	Lukas Wunner <lukas@...ner.de>,
	Ignat Korchagin <ignat@...udflare.com>,
	linux-crypto@...r.kernel.org, keyrings@...r.kernel.org,
	linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 2/9] crypto: Add ML-DSA/Dilithium verify support

On Mon, Nov 17, 2025 at 02:55:51PM +0000, David Howells wrote:
>  lib/crypto/Kconfig                            |   1 +
>  lib/crypto/Makefile                           |   2 +
>  lib/crypto/mldsa/Kconfig                      |  29 ++
>  lib/crypto/mldsa/Makefile                     |  20 +
>  lib/crypto/mldsa/crypto_mldsa_44.c            | 166 ++++++++
>  lib/crypto/mldsa/crypto_mldsa_65.c            | 166 ++++++++
>  lib/crypto/mldsa/crypto_mldsa_87.c            | 166 ++++++++
>  lib/crypto/mldsa/dilithium.h                  | 304 ++++++++++++++
>  lib/crypto/mldsa/dilithium_44.c               |  33 ++
>  lib/crypto/mldsa/dilithium_44.h               | 291 ++++++++++++++
>  lib/crypto/mldsa/dilithium_65.c               |  33 ++
>  lib/crypto/mldsa/dilithium_65.h               | 291 ++++++++++++++
>  lib/crypto/mldsa/dilithium_87.c               |  33 ++
>  lib/crypto/mldsa/dilithium_87.h               | 291 ++++++++++++++
>  lib/crypto/mldsa/dilithium_common.c           | 117 ++++++
>  lib/crypto/mldsa/dilithium_debug.h            |  49 +++
>  lib/crypto/mldsa/dilithium_ntt.c              |  89 +++++
>  lib/crypto/mldsa/dilithium_ntt.h              |  35 ++
>  lib/crypto/mldsa/dilithium_pack.h             | 119 ++++++
>  lib/crypto/mldsa/dilithium_poly.c             | 377 ++++++++++++++++++
>  lib/crypto/mldsa/dilithium_poly.h             | 181 +++++++++
>  lib/crypto/mldsa/dilithium_poly_c.h           | 141 +++++++
>  lib/crypto/mldsa/dilithium_poly_common.h      |  35 ++
>  lib/crypto/mldsa/dilithium_polyvec.h          | 343 ++++++++++++++++
>  lib/crypto/mldsa/dilithium_polyvec_c.h        |  81 ++++
>  lib/crypto/mldsa/dilithium_reduce.h           |  85 ++++
>  lib/crypto/mldsa/dilithium_rounding.c         | 128 ++++++
>  lib/crypto/mldsa/dilithium_service_helpers.h  |  99 +++++
>  lib/crypto/mldsa/dilithium_signature_c.c      | 279 +++++++++++++
>  lib/crypto/mldsa/dilithium_signature_c.h      |  37 ++
>  lib/crypto/mldsa/dilithium_signature_impl.h   | 370 +++++++++++++++++
>  lib/crypto/mldsa/dilithium_type.h             | 108 +++++
>  lib/crypto/mldsa/dilithium_zetas.c            |  68 ++++
>  .../mldsa/signature_domain_separation.c       | 204 ++++++++++
>  .../mldsa/signature_domain_separation.h       |  30 ++
>  35 files changed, 4801 insertions(+)

Over the past week I've been starting to review this massive addition.

I don't think this is on the right track.  This implementation is really
messy, with lots of unused functionality and unnecessary abstractions,
and code that doesn't follow kernel conventions.

In comparison, BoringSSL has an entire implementation of ML-DSA,
*including key generation and signing*, in a bit over 3000 lines in one
file.  But about half of that code is specific to key generation or
signing, which the kernel doesn't need, so in principle
verification-only shouldn't be much more than a thousand.  I find it to
be much easier to understand than leancrypto as well.

Historically we've had a lot of problems with people integrating code
from external sources into the kernel, like mpi, with properly "owning"
it because they feel like it's not their code and someone else is
responsible.  I feel like that's going to be a big problem here.

I think we can do better here and put together a smaller implementation
for the kernel that we'll actually be able to maintain.

- Eric