Re: SHAKE256 support

[Eric Biggers <ebiggers@kernel.org>]

On Wed, Sep 17, 2025 at 08:11:07PM +0100, David Howells wrote:
> Eric Biggers <ebiggers@kernel.org> wrote:
> 
> > On Wed, Sep 17, 2025 at 05:20:43PM +0100, David Howells wrote:
> > > Okay, I have lib/crypto/sha3 working.  One question though: why are the hash
> > > tests built as separate kunit modules rather than being built into the
> > > algorithm module init function and marked __init/__initdata?
> > 
> > KUnit is the standard way to do unit testing in the kernel these days.
> > The kernel community has been working on migrating legacy ad-hoc tests
> > over to KUnit.  This is not specific to lib/crypto/.
> 
> How do you test hashes with variable length digests (e.g. SHAKE128/256) using
> the hash testing infrastructure in lib/crypto/tests/?

Same as BLAKE2s
(https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git/tree/lib/crypto/tests/blake2s_kunit.c?h=libcrypto-next).
Just choose a fixed output length to use with hash-test-template.h, and
instantiate those test cases.  Then also add additional test cases to
your *_kunit.c file that cover other output lengths.

If you'd like to refactor things so that some of the variable-length
output test logic can be shared between the BLAKE2s and SHAKE tests,
that is a possibility.  But I expect it wouldn't be worthwhile yet.

- Eric