gpg: demo for subkeys decoding

trezor_agent/gpg/debug_subkeys.py

@@ -0,0 +1,46 @@
+#!/usr/bin/env python
+"""Check GPG v2 signature for a given public key."""
+import argparse
+import base64
+import io
+import logging
+import pprint
+
+from . import decode
+from .. import util
+
+log = logging.getLogger(__name__)
+
+
+def main():
+    """Main function."""
+    p = argparse.ArgumentParser()
+    p.add_argument('pubkey')
+    p.add_argument('-v', '--verbose', action='store_true', default=False)
+    args = p.parse_args()
+    logging.basicConfig(level=logging.DEBUG if args.verbose else logging.INFO,
+                        format='%(asctime)s %(levelname)-10s %(message)s')
+    stream = open(args.pubkey, 'rb')
+    parser = decode.Parser(util.Reader(stream))
+    pubkey, userid, sig1, subkey, sig2 = parser
+
+    digest = decode.digest_packets([pubkey, userid, sig1])
+    assert sig1['hash_prefix'] == digest[:2]
+    decode.verify_digest(
+        pubkey=pubkey, digest=digest,
+        signature=sig1['sig'], label='GPG public key (self sig)')
+
+    digest = decode.digest_packets([pubkey, subkey, sig2])
+    assert sig2['hash_prefix'] == digest[:2]
+    decode.verify_digest(
+        pubkey=pubkey, digest=digest,
+        signature=sig2['sig'], label='GPG subkey (1st sig)')
+
+    sig3, = sig2['embedded']
+    digest = decode.digest_packets([pubkey, subkey, sig3])
+    decode.verify_digest(
+        pubkey=subkey, digest=digest,
+        signature=sig3['sig'], label='GPG subkey (2nd sig)')
+
+if __name__ == '__main__':
+    main()

trezor_agent/gpg/decode.py

@@ -103,6 +103,15 @@ class Parser(object):
         p['_to_hash'] = p['content']
         return p
 
+    def _embedded_signatures(self, subpackets):
+        for packet in subpackets:
+            data = bytearray(packet)
+            if data[0] == 32:
+                # https://tools.ietf.org/html/rfc4880#section-5.2.3.26
+                stream = io.BytesIO(data[1:])
+                yield self.signature(util.Reader(stream))
+
+
     def signature(self, stream):
         """See https://tools.ietf.org/html/rfc4880#section-5.2 for details."""
         p = {'type': 'signature'}
@@ -121,6 +130,10 @@ class Parser(object):
         p['_to_hash'] = to_hash.getvalue() + tail_to_hash
 
         p['unhashed_subpackets'] = parse_subpackets(stream)
+        embedded = list(self._embedded_signatures(p['unhashed_subpackets']))
+        if embedded:
+            p['embedded'] = embedded
+
         p['hash_prefix'] = stream.readfmt('2s')
         p['sig'] = (parse_mpi(stream), parse_mpi(stream))
         assert not stream.read()
@@ -174,7 +187,9 @@ class Parser(object):
             mpi = parse_mpi(stream)
             log.debug('mpi: %x (%d bits)', mpi, mpi.bit_length())
             p['verifier'] = parser(mpi)
-            p['leftover'] = stream.read()  # TBD: what is this?
+            leftover = stream.read()  # TBD: what is this?
+            if leftover:
+                log.warning('unexpected subkey leftover: %r', leftover)
 
         # https://tools.ietf.org/html/rfc4880#section-12.2
         packet_data = packet.getvalue()