gpg: add compression and stronger digests

libagent/gpg/encode.py

@@ -23,9 +23,9 @@ def create_primary(user_id, pubkey, signer_func, secret_bytes=b''):
         # https://tools.ietf.org/html/rfc4880#section-5.2.3.4
         protocol.subpacket_byte(0x1B, 1 | 2),  # key flags (certify & sign)
         # https://tools.ietf.org/html/rfc4880#section-5.2.3.21
-        protocol.subpacket_byte(0x15, 8),  # preferred hash (SHA256)
+        protocol.subpacket_bytes(0x15, [8, 9, 10]),  # preferred hash
         # https://tools.ietf.org/html/rfc4880#section-5.2.3.8
-        protocol.subpacket_byte(0x16, 0),  # preferred compression (none)
+        protocol.subpacket_bytes(0x16, [2, 3, 1]),  # preferred compression
         # https://tools.ietf.org/html/rfc4880#section-5.2.3.9
         protocol.subpacket_byte(0x17, 0x80)  # key server prefs (no-modify)
         # https://tools.ietf.org/html/rfc4880#section-5.2.3.17

libagent/gpg/protocol.py

@@ -47,6 +47,11 @@ def subpacket_byte(subpacket_type, value):
     return subpacket(subpacket_type, '>B', value)
 
 
+def subpacket_bytes(subpacket_type, values):
+    """Create GPG subpacket with 8-bit unsigned integers."""
+    return subpacket(subpacket_type, '>' + 'B'*len(values), *values)
+
+
 def subpacket_prefix_len(item):
     """Prefix subpacket length according to RFC 4880 section-5.2.3.1."""
     n = len(item)