Verify the remote pubkey and peer_id

- Add `from_bytes` in RSAPublicKey and Secp256k1PublicKey
- Add `pubkey_from_protobuf` to parse pubkey from protobuf
- Verify key and peer_id in `InsecureSession.run_handshake`

libp2p/crypto/utils.py

@@ -0,0 +1,16 @@
+from .keys import PublicKey
+from .pb import crypto_pb2 as protobuf
+from .rsa import RSAPublicKey
+from .secp256k1 import Secp256k1PublicKey
+
+
+def pubkey_from_protobuf(pubkey_pb: protobuf.PublicKey) -> PublicKey:
+    if pubkey_pb.key_type == protobuf.RSA:
+        return RSAPublicKey.from_bytes(pubkey_pb.data)
+    # TODO: Test against secp256k1 keys
+    elif pubkey_pb.key_type == protobuf.Secp256k1:
+        return Secp256k1PublicKey.from_bytes(pubkey_pb.data)
+    else:
+        raise ValueError(
+            f"unsupported key_type={pubkey_pb.key_type}, data={pubkey_pb.data!r}"
+        )