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From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
Date:   Fri, 18 Dec 2020 17:14:58 +0100
Message-ID: <CAHmME9oW-_GXJ+nVwyiEV7wfjmzqBgqrSynnJ6xoN5UA_Nzh1Q@mail.gmail.com>
Subject: Re: [PATCH v2 09/11] crypto: blake2s - share the "shash" API
 boilerplate code
To:     Eric Biggers <ebiggers@kernel.org>
Cc:     Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        David Sterba <dsterba@suse.com>,
        Paul Crowley <paulcrowley@google.com>
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On Thu, Dec 17, 2020 at 11:25 PM Eric Biggers <ebiggers@kernel.org> wrote:
>
> From: Eric Biggers <ebiggers@google.com>
>
> Move the boilerplate code for setkey(), init(), update(), and final()
> from blake2s_generic.ko into a new module blake2s_helpers.ko, and export
> it so that it can be used by other shash implementations of BLAKE2s.
>
> setkey() and init() are exported as-is, while update() and final() have
> a blake2s_compress_t function pointer argument added.  This allows the
> implementation of the compression function to be overridden, which is
> the only part that optimized implementations really care about.
>
> The helper functions are defined in a separate module blake2s_helpers.ko
> (rather than just than in blake2s_generic.ko) because we can't simply
> select CRYPTO_BLAKE2B from CRYPTO_BLAKE2S_X86.  Doing this selection
> unconditionally would make the library API select the shash API, while
> doing it conditionally on CRYPTO_HASH would create a recursive kconfig
> dependency on CRYPTO_HASH.  As a bonus, using a separate module also
> allows the generic implementation to be omitted when unneeded.
>
> These helper functions very closely match the ones I defined for
> BLAKE2b, except the BLAKE2b ones didn't go in a separate module yet
> because BLAKE2b isn't exposed through the library API yet.
>
> Finally, use these new helper functions in the x86 implementation of
> BLAKE2s.  (This part should be a separate patch, but unfortunately the
> x86 implementation used the exact same function names like
> "crypto_blake2s_update()", so it had to be updated at the same time.)

There's a similar situation happening with chacha20poly1305 and with
curve25519. Each of these uses a mildly different approach to how we
split things up between library and crypto api code. The _helpers.ko
is another one. There any opportunity here to take a more
unified/consistant approach? Or is shash slightly different than the
others and benefits from a third way?

Jason