Merge pull request #16 from jhoenicke/master

More robust gpg key parsing

trezor_agent/gpg/agent.py

@@ -2,6 +2,7 @@
 import binascii
 import contextlib
 import logging
+import os
 
 from . import decode, encode, keyring
 from .. import util
@@ -39,8 +40,9 @@ def sig_encode(r, s):
 def pksign(keygrip, digest, algo):
     """Sign a message digest using a private EC key."""
     assert algo == '8'
+    user_id = os.environ['TREZOR_GPG_USER_ID']
     pubkey_dict = decode.load_public_key(
-        pubkey_bytes=keyring.export_public_key(user_id=None),
+        pubkey_bytes=keyring.export_public_key(user_id=user_id),
         use_custom=True, ecdh=False)
     pubkey, conn = encode.load_from_public_key(pubkey_dict=pubkey_dict)
     with contextlib.closing(conn):
@@ -83,8 +85,9 @@ def pkdecrypt(keygrip, conn):
     assert keyring.recvline(conn) == b'END'
     remote_pubkey = parse_ecdh(line)
 
+    user_id = os.environ['TREZOR_GPG_USER_ID']
     local_pubkey = decode.load_public_key(
-        pubkey_bytes=keyring.export_public_key(user_id=None),
+        pubkey_bytes=keyring.export_public_key(user_id=user_id),
         use_custom=True, ecdh=True)
     pubkey, conn = encode.load_from_public_key(pubkey_dict=local_pubkey)
     with contextlib.closing(conn):

trezor_agent/gpg/decode.py

@@ -241,31 +241,62 @@ def parse_packets(stream):
 
         log.debug('prefix byte: %s', bin(value))
         assert util.bit(value, 7) == 1
-        assert util.bit(value, 6) == 0  # new format not supported yet
 
         tag = util.low_bits(value, 6)
+        if util.bit(value, 6) == 0:
             length_type = util.low_bits(tag, 2)
             tag = tag >> 2
             fmt = {0: '>B', 1: '>H', 2: '>L'}[length_type]
             packet_size = stream.readfmt(fmt)
+        else:
+            first = stream.readfmt('B')
+            if first < 192:
+                packet_size = first
+            elif first < 224:
+                packet_size = ((first - 192) << 8) + stream.readfmt('B') + 192
+            elif first == 255:
+                packet_size = stream.readfmt('>L')
+            else:
+                log.error('Partial Body Lengths unsupported')
 
         log.debug('packet length: %d', packet_size)
         packet_data = stream.read(packet_size)
         packet_type = PACKET_TYPES.get(tag)
-        assert packet_type is not None, tag
 
+        if packet_type is not None:
             p = packet_type(util.Reader(io.BytesIO(packet_data)))
             p['tag'] = tag
+        else:
+            p = {'type': 'unknown', 'tag': tag, 'raw': packet_data}
+
         log.debug('packet "%s": %s', p['type'], p)
         yield p
 
 
-def digest_packets(packets):
+def digest_packets(packets, hashalg):
     """Compute digest on specified packets, according to '_to_hash' field."""
     data_to_hash = io.BytesIO()
     for p in packets:
         data_to_hash.write(p['_to_hash'])
-    return hashlib.sha256(data_to_hash.getvalue()).digest()
+    return hashalg(data_to_hash.getvalue()).digest()
+
+
+def _hash_ripemd160(msg):
+    """Wrapper for ripemd160 hash."""
+    h = hashlib.new("ripemd160")
+    h.update(msg)
+    return h
+
+
+HASH_ALGORITHMS = {
+    1: hashlib.md5,
+    2: hashlib.sha1,
+    3: _hash_ripemd160,
+    8: hashlib.sha256,
+    9: hashlib.sha384,
+    10: hashlib.sha512,
+    11: hashlib.sha224,
+}
 
 
 def load_public_key(pubkey_bytes, use_custom=False, ecdh=False):
@@ -275,10 +306,13 @@ def load_public_key(pubkey_bytes, use_custom=False, ecdh=False):
     pubkey, userid, signature = packets[:3]
     packets = packets[3:]
 
-    digest = digest_packets([pubkey, userid, signature])
+    hashalg = HASH_ALGORITHMS.get(signature['hash_alg'])
+    if hashalg is not None:
+        digest = digest_packets([pubkey, userid, signature], hashalg)
         assert signature['hash_prefix'] == digest[:2]
+
     log.debug('loaded public key "%s"', userid['value'])
-    if pubkey.get('verifier'):
+    if hashalg is not None and pubkey.get('verifier'):
         verify_digest(pubkey=pubkey, digest=digest,
                       signature=signature['sig'], label='GPG public key')
     else:
@@ -292,6 +326,8 @@ def load_public_key(pubkey_bytes, use_custom=False, ecdh=False):
                 log.debug('found custom %s', packet['type'])
                 break
 
+        while packets[1]['type'] != 'signature':
+            packets = packets[1:]
         packet, signature = packets[:2]
         packets = packets[2:]
 
@@ -303,7 +339,9 @@ def load_public_key(pubkey_bytes, use_custom=False, ecdh=False):
 def load_signature(stream, original_data):
     """Load signature from stream, and compute GPG digest for verification."""
     signature, = list(parse_packets(util.Reader(stream)))
-    digest = digest_packets([{'_to_hash': original_data}, signature])
+    hashalg = HASH_ALGORITHMS.get(signature['hash_alg'])
+    assert hashalg is not None
+    digest = digest_packets([{'_to_hash': original_data}, signature], hashalg)
     assert signature['hash_prefix'] == digest[:2]
     return signature, digest
 

trezor_agent/gpg/tests/test_decode.py

@@ -1,3 +1,4 @@
+import hashlib
 import io
 
 import pytest
@@ -64,7 +65,7 @@ zpR9luXTKwMEl+mlZmwEFKZXBmir
         '_to_hash': b'\x04\x13\x13\x08\x00\x12\x05\x02WHH\xd6\x02\x1b\x03\x02\x15\x08\x02\x16\x00\x02\x17\x80\x04\xff\x00\x00\x00\x18'  # nopep8
     })
 
-    digest = decode.digest_packets(packets=[pubkey, user_id, signature])
+    digest = decode.digest_packets(packets=[pubkey, user_id, signature], hashalg=hashlib.sha256)
     decode.verify_digest(pubkey=pubkey, digest=digest,
                          signature=signature['sig'],
                          label='GPG primary public key')