Re: [PATCH 2/2] crypto: ecdsa - Use ecc_digits_from_bytes to convert signature

[Jarkko Sakkinen]

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 convert the r and s
> components of the signature to digits directly from the input byte
> array. This avoids going through an intermediate byte array that has the
> first few bytes filled with zeros.
>
> Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
> ---
>  crypto/ecdsa.c | 12 ++----------
>  1 file changed, 2 insertions(+), 10 deletions(-)
>
> diff --git a/crypto/ecdsa.c b/crypto/ecdsa.c
> index fa029f36110b..941cdc2b889b 100644
> --- a/crypto/ecdsa.c
> +++ b/crypto/ecdsa.c
> @@ -38,7 +38,6 @@ static int ecdsa_get_signature_rs(u64 *dest, size_t hdrlen, unsigned char tag,
>  	size_t bufsize = ndigits * sizeof(u64);
>  	ssize_t diff = vlen - bufsize;
>  	const char *d = value;
> -	u8 rs[ECC_MAX_BYTES];
>  
>  	if (!value || !vlen)
>  		return -EINVAL;
> @@ -46,7 +45,7 @@ static int ecdsa_get_signature_rs(u64 *dest, size_t hdrlen, unsigned char tag,
>  	/* diff = 0: 'value' has exacly the right size
>  	 * diff > 0: 'value' has too many bytes; one leading zero is allowed that
>  	 *           makes the value a positive integer; error on more
> -	 * diff < 0: 'value' is missing leading zeros, which we add
> +	 * diff < 0: 'value' is missing leading zeros
>  	 */
>  	if (diff > 0) {
>  		/* skip over leading zeros that make 'value' a positive int */
> @@ -61,14 +60,7 @@ static int ecdsa_get_signature_rs(u64 *dest, size_t hdrlen, unsigned char tag,
>  	if (-diff >= bufsize)
>  		return -EINVAL;
>  
> -	if (diff) {
> -		/* leading zeros not given in 'value' */
> -		memset(rs, 0, -diff);
> -	}
> -
> -	memcpy(&rs[-diff], d, vlen);
> -
> -	ecc_swap_digits((u64 *)rs, dest, ndigits);
> +	ecc_digits_from_bytes(d, vlen, dest, ndigits);
>  
>  	return 0;
>  }

Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>

BR, Jarkko