- Updates for experimental ARC support:

- Limit to rsa-sha256, rsa-sha1 not used by ARC and multi-signature
        design TBD

dkim/crypto.py

@@ -23,6 +23,7 @@
 __all__ = [
     'DigestTooLargeError',
     'HASH_ALGORITHMS',
+    'ARC_HASH_ALGORITHMS',
     'parse_pem_private_key',
     'parse_private_key',
     'parse_public_key',
@@ -85,6 +86,10 @@ HASH_ALGORITHMS = {
     b'ed25519-sha256': hashlib.sha256
     }
 
+ARC_HASH_ALGORITHMS = {
+    b'rsa-sha256': hashlib.sha256,
+    }
+
 # These values come from RFC 8017, section 9.2 Notes, page 46.
 HASH_ID_MAP = {
     'sha1': b"\x2b\x0e\x03\x02\x1a",