Re: [PATCH net-next v5 09/20] zinc: Poly1305 ARM and ARM64 implementations

[Jason A. Donenfeld]

Hi Eric,

On Wed, Sep 19, 2018 at 12:55 AM Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
> This will compute the wrong digest if called with simd_context=HAVE_FULL_SIMD
> and then later with simd_context=HAVE_NO_SIMD, since poly1305_blocks_neon()
> converts the accumulator from base 32 to base 26, whereas poly1305_blocks_arm()
> assumes it is still in base 32.  Is that intentional?  I'm sure this is a rare
> case, but my understanding is that the existing crypto API doesn't preclude
> calling successive steps in different contexts.  And I'm concerned that it could
> be relevant in some cases, e.g. especially if people are importing a hash state
> that was exported earlier.  Handling it by silently computing the wrong digest
> is not a great idea...

Indeed you're right; Samuel and I were just discussing that recently.
I'd rather handle this correctly even if the contexts change, so I'll
see if I can fix this up properly for that unlikely case in the next
revision.

Jason