gpg: support Curve25519 for creating encryption subkeys

trezor_agent/formats.py

@@ -11,11 +11,15 @@ from . import util
 
 log = logging.getLogger(__name__)
 
-# Supported ECDSA curves
+# Supported ECDSA curves (for SSH and GPG)
 CURVE_NIST256 = 'nist256p1'
 CURVE_ED25519 = 'ed25519'
 SUPPORTED_CURVES = {CURVE_NIST256, CURVE_ED25519}
 
+# Supported ECDH curves (for GPG)
+ECDH_NIST256 = 'nist256p1'
+ECDH_CURVE25519 = 'curve25519'
+
 # SSH key types
 SSH_NIST256_DER_OCTET = b'\x04'
 SSH_NIST256_KEY_PREFIX = b'ecdsa-sha2-'
@@ -134,7 +138,8 @@ def decompress_pubkey(pubkey, curve_name):
     if len(pubkey) == 33:
         decompress = {
             CURVE_NIST256: _decompress_nist256,
-            CURVE_ED25519: _decompress_ed25519
+            CURVE_ED25519: _decompress_ed25519,
+            ECDH_CURVE25519: _decompress_ed25519,
         }[curve_name]
         vk = decompress(pubkey)
 
@@ -192,3 +197,11 @@ def import_public_key(line):
     assert result['type'] == file_type.encode('ascii')
     log.debug('loaded %s public key: %s', file_type, result['fingerprint'])
     return result
+
+
+def get_ecdh_curve_name(signature_curve_name):
+    """Return appropriate curve for ECDH for specified signing curve."""
+    return {
+        CURVE_NIST256: ECDH_NIST256,
+        CURVE_ED25519: ECDH_CURVE25519,
+    }[signature_curve_name]

trezor_agent/gpg/__main__.py

@@ -8,7 +8,7 @@ import sys
 import time
 
 from . import agent, device, encode, keyring, protocol
-from .. import server
+from .. import formats, server
 
 log = logging.getLogger(__name__)
 
@@ -32,8 +32,8 @@ def run_create(args):
             verifying_key=verifying_key, ecdh=False)
         # subkey for encryption
         encryption_key = protocol.PublicKey(
-            curve_name=args.ecdsa_curve, created=args.time,
-            verifying_key=decryption_key, ecdh=True)
+            curve_name=formats.get_ecdh_curve_name(args.ecdsa_curve),
+            created=args.time, verifying_key=decryption_key, ecdh=True)
         result = encode.create_subkey(primary_bytes=primary_bytes,
                                       pubkey=signing_key,
                                       signer_func=conn.sign)
@@ -47,8 +47,8 @@ def run_create(args):
             verifying_key=verifying_key, ecdh=False)
         # subkey for encryption
         subkey = protocol.PublicKey(
-            curve_name=args.ecdsa_curve, created=args.time,
-            verifying_key=decryption_key, ecdh=True)
+            curve_name=formats.get_ecdh_curve_name(args.ecdsa_curve),
+            created=args.time, verifying_key=decryption_key, ecdh=True)
 
         result = encode.create_primary(user_id=user_id,
                                        pubkey=primary,

trezor_agent/gpg/device.py

@@ -17,12 +17,16 @@ class HardwareSigner(object):
     def pubkey(self, ecdh=False):
         """Return public key as VerifyingKey object."""
         addr = util.get_bip32_address(identity=self.identity, ecdh=ecdh)
+        if ecdh:
+            curve_name = formats.get_ecdh_curve_name(self.curve_name)
+        else:
+            curve_name = self.curve_name
         public_node = self.client_wrapper.connection.get_public_node(
-            n=addr, ecdsa_curve_name=self.curve_name)
+            n=addr, ecdsa_curve_name=curve_name)
 
         return formats.decompress_pubkey(
             pubkey=public_node.node.public_key,
-            curve_name=self.curve_name)
+            curve_name=curve_name)
 
     def sign(self, digest):
         """Sign the digest and return a serialized signature."""
@@ -40,7 +44,7 @@ class HardwareSigner(object):
         result = self.client_wrapper.connection.get_ecdh_session_key(
             identity=self.identity,
             peer_public_key=pubkey,
-            ecdsa_curve_name=self.curve_name)
+            ecdsa_curve_name=formats.get_ecdh_curve_name(self.curve_name))
         assert len(result.session_key) == 65
         assert result.session_key[:1] == b'\x04'
         return result.session_key

trezor_agent/gpg/protocol.py

@@ -141,7 +141,13 @@ SUPPORTED_CURVES = {
         'algo_id': 22,
         'serialize': _serialize_ed25519,
         'keygrip': _keygrip_ed25519,
-    }
+    },
+    formats.ECDH_CURVE25519: {
+        'oid': b'\x2B\x06\x01\x04\x01\x97\x55\x01\x05\x01',
+        'algo_id': 18,
+        'serialize': _serialize_ed25519,
+        'keygrip': _keygrip_ed25519,
+    },
 }
 
 ECDH_ALGO_ID = 18