Re: [PATCH crypto-next v3 1/3] crypto: poly1305 - add new 32 and 64-bit generic versions

[Eric Biggers <ebiggers@kernel.org>]

On Thu, Dec 12, 2019 at 06:32:56PM +0100, Jason A. Donenfeld wrote:
> diff --git a/include/crypto/internal/poly1305.h b/include/crypto/internal/poly1305.h
> index 479b0cab2a1a..ad97819711eb 100644
> --- a/include/crypto/internal/poly1305.h
> +++ b/include/crypto/internal/poly1305.h
> @@ -11,11 +11,12 @@
>  #include <crypto/poly1305.h>
>  
>  /*
> - * Poly1305 core functions.  These implement the ε-almost-∆-universal hash
> + * Poly1305 core functions.  These can implement the ε-almost-∆-universal hash
>   * function underlying the Poly1305 MAC, i.e. they don't add an encrypted nonce
> - * ("s key") at the end.  They also only support block-aligned inputs.
> + * ("s key") at the end, by passing NULL to nonce.  They also only support
> + * block-aligned inputs.
>   */

This comment is now ambiguous because the "i.e." clause wasn't updated to match
the change "implement" => "can implement".

This comment also wasn't updated when the 'hibit' argument was added earlier
anyway.  So how about just rewriting it like:

/*
 * Poly1305 core functions.  These only accept whole blocks; the caller must
 * handle any needed block buffering and padding.  'hibit' must be 1 for any
 * full blocks, or 0 for the final block if it had to be padded.  If 'nonce' is
 * non-NULL, then it's added at the end to compute the Poly1305 MAC.  Otherwise,
 * only the ε-almost-∆-universal hash function (not the full MAC) is computed.
 */                                                          

> diff --git a/include/crypto/nhpoly1305.h b/include/crypto/nhpoly1305.h
> index 53c04423c582..a2f4e37b5107 100644
> --- a/include/crypto/nhpoly1305.h
> +++ b/include/crypto/nhpoly1305.h
> @@ -33,7 +33,7 @@
>  #define NHPOLY1305_KEY_SIZE	(POLY1305_BLOCK_SIZE + NH_KEY_BYTES)
>  
>  struct nhpoly1305_key {
> -	struct poly1305_key poly_key;
> +	struct poly1305_key poly_key[2];
>  	u32 nh_key[NH_KEY_WORDS];
>  };

I still feel that this makes the code worse.  Before, poly1305_key was an opaque
type that represented a Poly1305 key.  After, users would need to know that an
array of 2 "keys" is needed, despite there actually being only one key.

Given that this even caused an actual bug in v1 of this series, how about going
with a less error-prone approach?

> +void poly1305_core_blocks(struct poly1305_state *state,
> +			  const struct poly1305_key *key, const void *src,
> +			  unsigned int nblocks, u32 hibit)
> +{
> +	const u8 *input = src;
> +	u32 r0, r1, r2, r3, r4;
> +	u32 s1, s2, s3, s4;
> +	u32 h0, h1, h2, h3, h4;
> +	u64 d0, d1, d2, d3, d4;
> +	u32 c;
> +
> +	if (!nblocks)
> +		return;
> +
> +	hibit <<= 24;
> +
> +	r0 = key[0].r[0];
> +	r1 = key[0].r[1];
> +	r2 = key[0].r[2];
> +	r3 = key[0].r[3];
> +	r4 = key[0].r[4];
> +
> +	s1 = key[1].r[0];
> +	s2 = key[1].r[1];
> +	s3 = key[1].r[2];
> +	s4 = key[1].r[3];

And some of the function prototypes, like this one, still give no indication
that 2 "keys" are needed...

- Eric