[PATCH v3 4/5] lib: mbedtls: sha256: add support of key derivation

[Raymond Mao]

Hi Philippe,

On Mon, 9 Dec 2024 at 04:42, Philippe Reynes <philippe.reynes at softathome.com>
wrote:

> Adds the support of key derivation using the scheme hkdf.
> This scheme is defined in rfc5869.
>
> Signed-off-by: Philippe Reynes <philippe.reynes at softathome.com>
> ---
>  include/u-boot/sha256.h |  7 +++++++
>  lib/mbedtls/sha256.c    | 22 ++++++++++++++++++++++
>  2 files changed, 29 insertions(+)
>
> diff --git a/include/u-boot/sha256.h b/include/u-boot/sha256.h
> index 2f12275b703..5643efcb85c 100644
> --- a/include/u-boot/sha256.h
> +++ b/include/u-boot/sha256.h
> @@ -49,4 +49,11 @@ void sha256_hmac(const unsigned char *key, int keylen,
>                  const unsigned char *input, unsigned int ilen,
>                  unsigned char *output);
>
> +#if defined(CONFIG_HKDF_MBEDTLS)
> +int sha256_hkdf(const unsigned char *salt, int saltlen,
> +               const unsigned char *ikm, int ikmlen,
> +               const unsigned char *info, int infolen,
> +               unsigned char *output, int outputlen);
> +#endif
> +
>

I think this will be better:
#if CONFIG_IS_ENABLED(HKDF_MBEDTLS)
int sha256_hkdf(const unsigned char *salt, int saltlen,
                 const unsigned char *ikm, int ikmlen,
                 const unsigned char *info, int infolen,
                 unsigned char *output, int outputlen);
#else
static inline int sha256_hkdf(const unsigned char __always_unused *salt,
                int __always_unused saltlen,
                const unsigned char __always_unused *ikm,
                int __always_unused ikmlen,
                const unsigned char __always_unused *info,
                int __always_unused infolen,
                unsigned char __always_unused *output,
                int __always_unused outputlen) {
        return -EOPNOTSUPP;
}
#endif


>  #endif /* _SHA256_H */
> diff --git a/lib/mbedtls/sha256.c b/lib/mbedtls/sha256.c
> index 1b9fc1a8503..6e9659d31bb 100644
> --- a/lib/mbedtls/sha256.c
> +++ b/lib/mbedtls/sha256.c
> @@ -11,6 +11,11 @@
>  #include <string.h>
>  #include <u-boot/sha256.h>
>
> +#if CONFIG_IS_ENABLED(HKDF_MBEDTLS)
> +#include <mbedtls/md.h>
> +#include <mbedtls/hkdf.h>
> +#endif
> +
>  const u8 sha256_der_prefix[SHA256_DER_LEN] = {
>         0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86,
>         0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05,
> @@ -98,3 +103,20 @@ void sha256_hmac(const unsigned char *key, int keylen,
>         memset(tmpbuf, 0, sizeof(tmpbuf));
>         memset(&ctx, 0, sizeof(sha256_context));
>  }
> +
> +#if CONFIG_IS_ENABLED(HKDF_MBEDTLS)
> +int sha256_hkdf(const unsigned char *salt, int saltlen,
> +               const unsigned char *ikm, int ikmlen,
> +               const unsigned char *info, int infolen,
> +               unsigned char *output, int outputlen)
> +{
> +       const mbedtls_md_info_t *md;
> +
> +       md = mbedtls_md_info_from_type(MBEDTLS_MD_SHA256);
> +
> +       return mbedtls_hkdf(md, salt, saltlen,
> +                           ikm, ikmlen,
> +                           info, infolen,
> +                           output, outputlen);
> +}
> +#endif
> --
> 2.25.1
>
>