Re: [PATCH 1/2] crypto: ecdsa - Use ecc_digits_from_bytes to create hash digits array

[Jarkko Sakkinen]

On Thu May 30, 2024 at 3:24 PM EEST, Stefan Berger wrote:
>
>
> On 5/30/24 01:28, Jarkko Sakkinen wrote:
> > On Thu May 30, 2024 at 2:08 AM EEST, Stefan Berger wrote:
> >> Since ecc_digits_from_bytes will provide zeros when an insufficient number
> >> of bytes are passed in the input byte array, use it to create the hash
> >> digits directly from the input byte array. This avoids going through an
> >> intermediate byte array (rawhash) that has the first few bytes filled with
> >> zeros.
> >>
> >> Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
> >> ---
> >>   crypto/ecdsa.c | 17 ++++-------------
> >>   1 file changed, 4 insertions(+), 13 deletions(-)
> >>
> >> diff --git a/crypto/ecdsa.c b/crypto/ecdsa.c
> >> index 258fffbf623d..fa029f36110b 100644
> >> --- a/crypto/ecdsa.c
> >> +++ b/crypto/ecdsa.c
> >> @@ -142,10 +142,8 @@ static int ecdsa_verify(struct akcipher_request *req)
> >>   	struct ecdsa_signature_ctx sig_ctx = {
> >>   		.curve = ctx->curve,
> >>   	};
> >> -	u8 rawhash[ECC_MAX_BYTES];
> >>   	u64 hash[ECC_MAX_DIGITS];
> >>   	unsigned char *buffer;
> >> -	ssize_t diff;
> >>   	int ret;
> >>   
> >>   	if (unlikely(!ctx->pub_key_set))
> >> @@ -164,18 +162,11 @@ static int ecdsa_verify(struct akcipher_request *req)
> >>   	if (ret < 0)
> >>   		goto error;
> >>   
> >> -	/* if the hash is shorter then we will add leading zeros to fit to ndigits */
> >> -	diff = bufsize - req->dst_len;
> >> -	if (diff >= 0) {
> >> -		if (diff)
> >> -			memset(rawhash, 0, diff);
> >> -		memcpy(&rawhash[diff], buffer + req->src_len, req->dst_len);
> >> -	} else if (diff < 0) {
> >> -		/* given hash is longer, we take the left-most bytes */
> >> -		memcpy(&rawhash, buffer + req->src_len, bufsize);
> >> -	}
> >> +	if (bufsize > req->dst_len)
> >> +		bufsize = req->dst_len;
> >>   
> >> -	ecc_swap_digits((u64 *)rawhash, hash, ctx->curve->g.ndigits);
> >> +	ecc_digits_from_bytes(buffer + req->src_len, bufsize,
> >> +			      hash, ctx->curve->g.ndigits);
> >>   
> >>   	ret = _ecdsa_verify(ctx, hash, sig_ctx.r, sig_ctx.s);
> >>   
> > 
> > Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> > 
> > I don't think it'd be even nit-picking to say that the function
> > called would really need kdoc. I had to spend about 20 minutes
> > to reacall ecc_digits_from_bytes().
>
> Here's the file with all the kdocs: 
> https://elixir.bootlin.com/linux/v6.10-rc1/source/include/crypto/internal/ecc.h#L67

LOL, sorry I forgot this. I think this was the 2nd time I complained
about this ;-) I'm sorry, yeah that WFM.

Just not used to this convention but I don't mind actually if it is
that way.

BR, Jarkko