[PATCH v3 2/5] lib: sha256: add feature sha256_hmac

[Raymond Mao]

Hi Philippe,

On Mon, 9 Dec 2024 at 04:42, 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/mbedtls/sha256.c    | 38 ++++++++++++++++++++++++++++++++++++++
>  lib/sha256.c            | 37 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 79 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/mbedtls/sha256.c b/lib/mbedtls/sha256.c
> index 24aa58fa674..1b9fc1a8503 100644
> --- a/lib/mbedtls/sha256.c
> +++ b/lib/mbedtls/sha256.c
> @@ -8,6 +8,7 @@
>  #ifndef USE_HOSTCC
>  #include <cyclic.h>
>  #endif /* USE_HOSTCC */
> +#include <string.h>
>  #include <u-boot/sha256.h>
>
>  const u8 sha256_der_prefix[SHA256_DER_LEN] = {
> @@ -60,3 +61,40 @@ 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 k_ipad[64];
> +       unsigned char k_opad[64];
> +       unsigned char tmpbuf[32];
> +
> +       memset(k_ipad, 0x36, 64);
> +       memset(k_opad, 0x5C, 64);
> +
> +       for (i = 0; i < keylen; i++) {
> +               if (i >= 64)
> +                       break;
> +
> +               k_ipad[i] ^= key[i];
> +               k_opad[i] ^= key[i];
> +       }
> +
>

You are assuming that the key length is at most 64 bytes.
But according to the HMAC specification:
If the key is longer than the hash block size (64 bytes for SHA256),
it should be hashed first to produce a shorter key.
If the key is shorter than 64 bytes, it should be zero-padded to 64 bytes.


> +       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(&ctx, 0, sizeof(sha256_context));
> +}
> diff --git a/lib/sha256.c b/lib/sha256.c
> index fb195d988f1..66224c92dd9 100644
> --- a/lib/sha256.c
> +++ b/lib/sha256.c
> @@ -300,3 +300,40 @@ 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 k_ipad[64];
> +       unsigned char k_opad[64];
> +       unsigned char tmpbuf[32];
> +
> +       memset(k_ipad, 0x36, 64);
> +       memset(k_opad, 0x5C, 64);
> +
> +       for (i = 0; i < keylen; i++) {
> +               if (i >= 64)
> +                       break;
> +
> +               k_ipad[i] ^= key[i];
> +               k_opad[i] ^= key[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(&ctx, 0, sizeof(sha256_context));
> +}
>

I understand now we have duplicated 'shaX_csum_wd()' under lib and
lib/mbedtls.
That is because at the time when MbedTLS was added in, _csum_wd() is the
only
duplicated function and it is a trade-off comparing with creating a new
common
file for each algorithm.
But it is not the case if the number of these duplicated functions is
increasing.
Do you mind moving them into a common file with the one you created?
At least for sha256 with this patch I think.

Regards,
Raymond


> --
> 2.25.1
>
>