KEYS: Add identifier pointers to public_key_signature struct

Add key identifier pointers to public_key_signature struct so that they can
be used to retain the identifier of the key to be used to verify the
signature in both PKCS#7 and X.509.

Signed-off-by: David Howells <dhowells@redhat.com>

include/crypto/public_key.h

@@ -47,6 +47,7 @@ extern void public_key_free(struct public_key *key);
  * Public key cryptography signature data
  */
 struct public_key_signature {
+	struct asymmetric_key_id *auth_ids[2];
 	u8 *s;			/* Signature */
 	u32 s_size;		/* Number of bytes in signature */
 	u8 *digest;