Hello,
In testutils.h, there is a nettle-meta definition for MACs, similar to
hashes and ciphers:
/* FIXME: When interface stabilizes, move to nettle-meta.h */
struct nettle_mac
{
const char *name;
/* Size of the context struct */
unsigned context_size;
/* Size of digests */
unsigned digest_size;
/* Suggested key size; other sizes are sometimes possible. */
unsigned key_size;
nettle_set_key_func *set_key;
nettle_hash_update_func *update;
nettle_hash_digest_func *digest;
};
This is, however, not usable for HMAC, because Nettle build uses
-Wcast-function-type and the set_key member has an incompatible type
with hmac_*_set_key, which requires a key length argument as HMAC allows
arbitrary key length up to the hash block size.
Is there any plan to make it more generic and eventually move it to
nettle-meta.h? That would be particularly useful in applications
passing around HMAC functions (e.g., HKDF, deterministic ECDSA).
For example, I'm thinking to use nettle_hash_update_func for set_key and
provide a wrapper around other MACs which don't take key length,
something like:
void
_cmac_aes128_set_key(struct cmac_aes128_ctx *ctx,
size_t length, const uint8_t *key)
{
assert (length == AES128_KEY_LENGTH);
cmac_aes128_set_key (ctx, length, key);
}
Regards,
--
Daiki Ueno
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