RSA: Implement signature verification algorithm [PKCS#1 / RFC3447]

Implement RSA public key cryptography [PKCS#1 / RFC3447].  At this time, only
the signature verification algorithm is supported.  This uses the asymmetric
public key subtype to hold its key data.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/crypto/asymmetric_keys/public_key.h b/crypto/asymmetric_keys/public_key.h
index 1f86aad..5e5e356 100644
--- a/crypto/asymmetric_keys/public_key.h
+++ b/crypto/asymmetric_keys/public_key.h
@@ -26,3 +26,5 @@
 	int (*verify_signature)(const struct public_key *key,
 				const struct public_key_signature *sig);
 };
+
+extern const struct public_key_algorithm RSA_public_key_algorithm;