[PATCH v2 2/5] lib: sha256: add feature sha256_hmac

[Philippe REYNES]

Hi Raymond,

Le 05/12/2024 à 18:11, Raymond Mao a écrit :
>
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>
> Hi Philippe,
>
> On Wed, 4 Dec 2024 at 12:54, 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 ++++++++++++++++++++++++++++++++++++++
>      2 files changed, 42 insertions(+)
>
>     diff --git a/include/u-boot/sha256.h b/include/u-boot/sha256.h
>     index b58d5b58d39..77dbcd4553a 100644
>     --- a/include/u-boot/sha256.h
>     +++ b/include/u-boot/sha256.h
>     @@ -44,4 +44,8 @@ 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);
>     +
>
> Shall we have an inline function for the case if mbedtls is not enabled?


you're right, I should manage the case where mbedtls is not enabled.
But with you're feedback below, the function hmac is always defined (with
or without mbedtls).


>      #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];
>     +       }
>     +
>     +       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));
>     +}
>
>
> This function seems to be generic and should be located in lib instead 
> of lib/mbedtls.


I have looked the function sha256_csum_wd and I have seen that this function
is defined twice, in the file lib/sha256.c and in lib/mbedtls/sha256.c. 
I have done
the same to have the support of sha256_hmac with or without mbedtls.
But I think that we should avoid to duplicate code, and we should clean it.


>
> Regards,
> Raymond


Regards,
Philippe