[PATCH v4 5/8] lib: sha256: add feature sha256_hmac

[Raymond Mao]

Hi Philippe,

On Thu, 12 Dec 2024 at 08:37, Philippe Reynes <
philippe.reynes at softathome.com> wrote:

> Adds the support of the hmac based on sha256.
> This implementation is based on rfc2104.
>
> Signed-off-by: Philippe Reynes <philippe.reynes at softathome.com>
> ---
>  include/u-boot/sha256.h |  4 ++++
>  lib/sha256_common.c     | 48 +++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 52 insertions(+)
>
> diff --git a/include/u-boot/sha256.h b/include/u-boot/sha256.h
> index 44a9b528b48..2f12275b703 100644
> --- a/include/u-boot/sha256.h
> +++ b/include/u-boot/sha256.h
> @@ -45,4 +45,8 @@ void sha256_finish(sha256_context * ctx, uint8_t
> digest[SHA256_SUM_LEN]);
>  void sha256_csum_wd(const unsigned char *input, unsigned int ilen,
>                 unsigned char *output, unsigned int chunk_sz);
>
> +void sha256_hmac(const unsigned char *key, int keylen,
> +                const unsigned char *input, unsigned int ilen,
> +                unsigned char *output);
> +
>  #endif /* _SHA256_H */
> diff --git a/lib/sha256_common.c b/lib/sha256_common.c
> index 7041abd26d9..46262ea99a2 100644
> --- a/lib/sha256_common.c
> +++ b/lib/sha256_common.c
> @@ -48,3 +48,51 @@ void sha256_csum_wd(const unsigned char *input,
> unsigned int ilen,
>
>         sha256_finish(&ctx, output);
>  }
> +
> +void sha256_hmac(const unsigned char *key, int keylen,
> +                const unsigned char *input, unsigned int ilen,
> +                unsigned char *output)
> +{
> +       int i;
> +       sha256_context ctx;
> +       unsigned char keybuf[64];
> +       unsigned char k_ipad[64];
> +       unsigned char k_opad[64];
> +       unsigned char tmpbuf[32];
> +       int keybuf_len;
> +
> +       if (keylen > 64) {
> +               sha256_starts(&ctx);
> +               sha256_update(&ctx, key, keylen);
> +               sha256_finish(&ctx, keybuf);
> +
> +               keybuf_len = 32;
> +       } else {
> +               memcpy(keybuf, key, keylen);
> +               keybuf_len = keylen;
> +       }
> +
> +       memset(k_ipad, 0x36, 64);
> +       memset(k_opad, 0x5C, 64);
> +
> +       for (i = 0; i < keybuf_len; i++) {
> +               k_ipad[i] ^= keybuf[i];
> +               k_opad[i] ^= keybuf[i];
> +       }
> +
> +       sha256_starts(&ctx);
> +       sha256_update(&ctx, k_ipad, sizeof(k_ipad));
> +       sha256_update(&ctx, input, ilen);
> +       sha256_finish(&ctx, tmpbuf);
> +
> +       sha256_starts(&ctx);
> +       sha256_update(&ctx, k_opad, sizeof(k_opad));
> +       sha256_update(&ctx, tmpbuf, sizeof(tmpbuf));
> +       sha256_finish(&ctx, output);
> +
> +       memset(k_ipad, 0, sizeof(k_ipad));
> +       memset(k_opad, 0, sizeof(k_opad));
> +       memset(tmpbuf, 0, sizeof(tmpbuf));
> +       memset(keybuf, 0, sizeof(keybuf));
> +       memset(&ctx, 0, sizeof(sha256_context));
> +}
> --
> 2.25.1
>
> The sha256 hmac common implementation now sounds good.
Do you have a comparison of performance with the MbedTLS high-level API
mbedtls_md_hmac()?
I am wondering if it is worth using this API specially when MbedTLS is
enabled,
since it significantly simplifies the implementation.

Regards,
Raymond