HACK: create subkey with ECDH support

trezor_agent/gpg/__main__.py

@@ -16,7 +16,7 @@ def run_create(args):
     """Generate a new pubkey for a new/existing GPG identity."""
     user_id = os.environ['TREZOR_GPG_USER_ID']
     f = encode.Factory(user_id=user_id, created=args.time,
-                       curve_name=args.ecdsa_curve)
+                       curve_name=args.ecdsa_curve, ecdh=args.ecdh)
 
     with contextlib.closing(f):
         if args.subkey:
@@ -38,6 +38,7 @@ def main():
 
     create = subparsers.add_parser('create')
     create.add_argument('-s', '--subkey', action='store_true', default=False)
+    create.add_argument('--ecdh', action='store_true', default=False)
     create.add_argument('-e', '--ecdsa-curve', default='nist256p1')
     create.add_argument('-t', '--time', type=int, default=int(time.time()))
     create.set_defaults(run=run_create)

trezor_agent/gpg/encode.py

@@ -71,7 +71,7 @@ def _time_format(t):
 class Factory(object):
     """Performs GPG signing operations."""
 
-    def __init__(self, user_id, created, curve_name):
+    def __init__(self, user_id, created, curve_name, ecdh=False):
         """Construct and loads a public key from the device."""
         self.user_id = user_id
         assert curve_name in formats.SUPPORTED_CURVES
@@ -79,7 +79,8 @@ class Factory(object):
         self.conn = HardwareSigner(user_id, curve_name=curve_name)
         self.pubkey = proto.PublicKey(
             curve_name=curve_name, created=created,
-            verifying_key=self.conn.pubkey())
+            verifying_key=self.conn.pubkey(), ecdh=ecdh)
+        self.ecdh = ecdh
 
         log.info('%s created at %s for "%s"',
                  self.pubkey, _time_format(self.pubkey.created), user_id)
@@ -142,28 +143,38 @@ class Factory(object):
                  self.user_id, util.hexlify(primary['key_id']))
         data_to_sign = primary['_to_hash'] + self.pubkey.data_to_hash()
 
-        # Primary Key Binding Signature
-        hashed_subpackets = [
-            proto.subpacket_time(self.pubkey.created)]  # signature time
-        unhashed_subpackets = [
-            proto.subpacket(16, self.pubkey.key_id())]  # issuer key id
-        log.info('confirm signing subkey with hardware device')
-        embedded_sig = proto.make_signature(
-            signer_func=self.conn.sign,
-            data_to_sign=data_to_sign,
-            public_algo=self.pubkey.algo_id,
-            sig_type=0x19,
-            hashed_subpackets=hashed_subpackets,
-            unhashed_subpackets=unhashed_subpackets)
+        if self.ecdh:
+            embedded_sig = None
+        else:
+            # Primary Key Binding Signature
+            hashed_subpackets = [
+                proto.subpacket_time(self.pubkey.created)]  # signature time
+            unhashed_subpackets = [
+                proto.subpacket(16, self.pubkey.key_id())]  # issuer key id
+            log.info('confirm signing subkey with hardware device')
+            embedded_sig = proto.make_signature(
+                signer_func=self.conn.sign,
+                data_to_sign=data_to_sign,
+                public_algo=self.pubkey.algo_id,
+                sig_type=0x19,
+                hashed_subpackets=hashed_subpackets,
+                unhashed_subpackets=unhashed_subpackets)
 
         # Subkey Binding Signature
+        flags = 2  # key flags (certify & sign)
+        if self.ecdh:
+            flags = 4 | 8
+
         hashed_subpackets = [
             proto.subpacket_time(self.pubkey.created),  # signature time
-            proto.subpacket_byte(0x1B, 2)]  # key flags (certify & sign)
-        unhashed_subpackets = [
-            proto.subpacket(16, primary['key_id']),  # issuer key id
-            proto.subpacket(32, embedded_sig),
-            proto.CUSTOM_SUBPACKET]
+            proto.subpacket_byte(0x1B, flags)]
+
+        unhashed_subpackets = []
+        unhashed_subpackets.append(proto.subpacket(16, primary['key_id']))
+        if embedded_sig is not None:
+            unhashed_subpackets.append(proto.subpacket(32, embedded_sig))
+        unhashed_subpackets.append(proto.CUSTOM_SUBPACKET)
+
         log.info('confirm signing subkey with gpg-agent')
         gpg_agent = AgentSigner(self.user_id)
         signature = proto.make_signature(

trezor_agent/gpg/proto.py

@@ -131,6 +131,7 @@ SUPPORTED_CURVES = {
     }
 }
 
+ECDH_ALGO_ID = 18
 
 CUSTOM_SUBPACKET = subpacket(100, b'TREZOR-GPG')  # marks "our" pubkey
 
@@ -145,12 +146,18 @@ def find_curve_by_algo_id(algo_id):
 class PublicKey(object):
     """GPG representation for public key packets."""
 
-    def __init__(self, curve_name, created, verifying_key):
+    def __init__(self, curve_name, created, verifying_key, ecdh=False):
         """Contruct using a ECDSA VerifyingKey object."""
         self.curve_info = SUPPORTED_CURVES[curve_name]
         self.created = int(created)  # time since Epoch
         self.verifying_key = verifying_key
-        self.algo_id = self.curve_info['algo_id']
+        if ecdh:
+            self.algo_id = ECDH_ALGO_ID
+            self.ecdh_packet = b'\x03\x01\x08\x07'
+        else:
+            self.algo_id = self.curve_info['algo_id']
+            self.ecdh_packet = b''
+
         self.keygrip = self.curve_info['keygrip'](verifying_key)
         hex_key_id = util.hexlify(self.key_id())[-8:]
         self.desc = 'GPG public key {}/{}'.format(curve_name, hex_key_id)
@@ -163,7 +170,7 @@ class PublicKey(object):
                              self.algo_id)  # public key algorithm ID
         oid = util.prefix_len('>B', self.curve_info['oid'])
         blob = self.curve_info['serialize'](self.verifying_key)
-        return header + oid + blob
+        return header + oid + blob + self.ecdh_packet
 
     def data_to_hash(self):
         """Data for digest computation."""