Noise: complete handshake process

TODO
- Figure out why `state.rs` is erased at some moment(even handshake
is not done).
- Refactor
- Add tests

libp2p/security/noise/messages.py

@@ -0,0 +1,56 @@
+from dataclasses import dataclass
+
+from libp2p.crypto.keys import PrivateKey, PublicKey
+from libp2p.crypto.serialization import deserialize_public_key
+
+from .pb import noise_pb2 as noise_pb
+
+SIGNED_DATA_PREFIX = "noise-libp2p-static-key:"
+
+
+@dataclass
+class NoiseHandshakePayload:
+    id_pubkey: PublicKey
+    id_sig: bytes
+    early_data: bytes = None
+
+    def serialize(self) -> bytes:
+        msg = noise_pb.NoiseHandshakePayload(
+            identity_key=self.id_pubkey.serialize(), identity_sig=self.id_sig
+        )
+        if self.early_data is not None:
+            msg.data = self.early_data
+        return msg.SerializeToString()
+
+    @classmethod
+    def deserialize(cls, protobuf_bytes: bytes) -> "NoiseHandshakePayload":
+        msg = noise_pb.NoiseHandshakePayload.FromString(protobuf_bytes)
+        return cls(
+            id_pubkey=deserialize_public_key(msg.identity_key),
+            id_sig=msg.identity_sig,
+            early_data=msg.data if msg.data != b"" else None,
+        )
+
+
+def make_data_to_be_signed(noise_static_pubkey: PublicKey) -> bytes:
+    prefix_bytes = SIGNED_DATA_PREFIX.encode("utf-8")
+    return prefix_bytes + noise_static_pubkey.to_bytes()
+
+
+def make_handshake_payload_sig(
+    id_privkey: PrivateKey, noise_static_pubkey: PublicKey
+) -> bytes:
+    data = make_data_to_be_signed(noise_static_pubkey)
+    return id_privkey.sign(data)
+
+
+def verify_handshake_payload_sig(
+    payload: NoiseHandshakePayload, noise_static_pubkey: PublicKey
+) -> bool:
+    """
+    Verify if the signature
+        1. is composed of the data `SIGNED_DATA_PREFIX`++`noise_static_pubkey` and
+        2. signed by the private key corresponding to `id_pubkey`
+    """
+    expected_data = make_data_to_be_signed(noise_static_pubkey)
+    return payload.id_pubkey.verify(expected_data, payload.id_sig)