pylightning: Implement the lightning handshake and wire protocol

Simple transcript of the specification in python :-) Signed-off-by: Christian Decker <decker.christian@gmail.com>
6 years ago · 8fc813e0da
4 changed files with 575 additions and 1 deletions
--- a/contrib/pylightning/lightning/wire.py
+++ b/contrib/pylightning/lightning/wire.py
@ -0,0 +1,379 @@
+from binascii import hexlify
+from cryptography.exceptions import InvalidTag
+from cryptography.hazmat.backends import default_backend
+from cryptography.hazmat.primitives import hashes
+from cryptography.hazmat.primitives.asymmetric import ec
+from cryptography.hazmat.primitives.ciphers.aead import ChaCha20Poly1305
+from cryptography.hazmat.primitives.kdf.hkdf import HKDF
+from cryptography.hazmat.primitives import serialization
+from hashlib import sha256
+import coincurve
+import os
+import socket
+import struct
+
+
+def hkdf(ikm, salt=b"", info=b""):
+    hkdf = HKDF(
+        algorithm=hashes.SHA256(),
+        length=64,
+        salt=salt,
+        info=info,
+        backend=default_backend())
+
+    return hkdf.derive(ikm)
+
+
+def hkdf_two_keys(ikm, salt):
+    t = hkdf(ikm, salt)
+    return t[:32], t[32:]
+
+
+def ecdh(k, rk):
+    k = coincurve.PrivateKey(secret=k.rawkey)
+    rk = coincurve.PublicKey(data=rk.serializeCompressed())
+    a = k.ecdh(rk.public_key)
+    return Secret(a)
+
+
+def encryptWithAD(k, n, ad, plaintext):
+    chacha = ChaCha20Poly1305(k)
+    return chacha.encrypt(n, plaintext, ad)
+
+
+def decryptWithAD(k, n, ad, ciphertext):
+    chacha = ChaCha20Poly1305(k)
+    return chacha.decrypt(n, ciphertext, ad)
+
+
+class PrivateKey(object):
+    def __init__(self, rawkey):
+        assert len(rawkey) == 32 and isinstance(rawkey, bytes)
+        self.rawkey = rawkey
+        rawkey = int(hexlify(rawkey), base=16)
+        self.key = ec.derive_private_key(rawkey, ec.SECP256K1(),
+                                         default_backend())
+
+    def serializeCompressed(self):
+        return self.key.private_bytes(serialization.Encoding.Raw,
+                                      serialization.PrivateFormat.Raw, None)
+
+    def public_key(self):
+        return PublicKey(self.key.public_key())
+
+
+class Secret(object):
+    def __init__(self, raw):
+        assert(len(raw) == 32)
+        self.raw = raw
+
+    def __str__(self):
+        return "Secret[0x{}]".format(hexlify(self.raw).decode('ASCII'))
+
+
+class PublicKey(object):
+    def __init__(self, innerkey):
+        # We accept either 33-bytes raw keys, or an EC PublicKey as returned
+        # by cryptography.io
+        if isinstance(innerkey, bytes):
+            innerkey = ec.EllipticCurvePublicKey.from_encoded_point(
+                ec.SECP256K1(), innerkey
+            )
+
+        elif not isinstance(innerkey, ec.EllipticCurvePublicKey):
+            raise ValueError(
+                "Key must either be bytes or ec.EllipticCurvePublicKey"
+            )
+        self.key = innerkey
+
+    def serializeCompressed(self):
+        raw = self.key.public_bytes(
+            serialization.Encoding.X962,
+            serialization.PublicFormat.CompressedPoint
+        )
+        return raw
+
+    def __str__(self):
+        return "PublicKey[0x{}]".format(
+            hexlify(self.serializeCompressed()).decode('ASCII')
+        )
+
+
+def Keypair(object):
+    def __init__(self, priv, pub):
+        self.priv, self.pub = priv, pub
+
+
+class Sha256Mixer(object):
+    def __init__(self, base):
+        self.hash = sha256(base).digest()
+
+    def update(self, data):
+        h = sha256(self.hash)
+        h.update(data)
+        self.hash = h.digest()
+        return self.hash
+
+    def digest(self):
+        return self.hash
+
+    def __str__(self):
+        return "Sha256Mixer[0x{}]".format(hexlify(self.hash).decode('ASCII'))
+
+
+class LightningConnection(object):
+    def __init__(self, connection, remote_pubkey, local_privkey, is_initiator):
+        self.connection = connection
+        self.chaining_key = None
+        self.handshake_hash = None
+        self.local_privkey = local_privkey
+        self.local_pubkey = self.local_privkey.public_key()
+        self.remote_pubkey = remote_pubkey
+        self.is_initiator = is_initiator
+        self.init_handshake()
+        self.rn, self.sn = 0, 0
+
+    @classmethod
+    def nonce(cls, n):
+        """Transforms a numeric nonce into a byte formatted one
+
+        Nonce n encoded as 32 zero bits, followed by a little-endian 64-bit
+        value. Note: this follows the Noise Protocol convention, rather than
+        our normal endian.
+        """
+        return b'\x00' * 4 + struct.pack("<Q", n)
+
+    def init_handshake(self):
+        h = sha256(b'Noise_XK_secp256k1_ChaChaPoly_SHA256').digest()
+        self.chaining_key = h
+        h = sha256(h + b'lightning').digest()
+
+        if self.is_initiator:
+            responder_pubkey = self.remote_pubkey
+        else:
+            responder_pubkey = self.local_pubkey
+        h = sha256(h + responder_pubkey.serializeCompressed()).digest()
+
+        self.handshake = {
+            'h': h,
+            'e': PrivateKey(os.urandom(32)),
+        }
+
+    def handshake_act_one_initiator(self):
+        h = Sha256Mixer(b'')
+        h.hash = self.handshake['h']
+        h.update(self.handshake['e'].public_key().serializeCompressed())
+        es = ecdh(self.handshake['e'], self.remote_pubkey)
+        t = hkdf(salt=self.chaining_key, ikm=es.raw, info=b'')
+        assert(len(t) == 64)
+        self.chaining_key, temp_k1 = t[:32], t[32:]
+        c = encryptWithAD(temp_k1, self.nonce(0), h.digest(), b'')
+        self.handshake['h'] = h.update(c)
+        pk = self.handshake['e'].public_key().serializeCompressed()
+        m = b'\x00' + pk + c
+        return m
+
+    def handshake_act_one_responder(self, m):
+        v, re, c = m[0], PublicKey(m[1:34]), m[34:]
+        if v != 0:
+            raise ValueError("Unsupported handshake version {}, only version "
+                             "0 is supported.".format(v))
+
+        h = Sha256Mixer(b'')
+        h.hash = self.handshake['h']
+        h.update(re.serializeCompressed())
+        es = ecdh(self.local_privkey, re)
+        self.handshake['re'] = re
+        t = hkdf(salt=self.chaining_key, ikm=es.raw, info=b'')
+        self.chaining_key, temp_k1 = t[:32], t[32:]
+
+        try:
+            decryptWithAD(temp_k1, self.nonce(0), h.digest(), c)
+        except InvalidTag:
+            ValueError("Verification of tag failed, remote peer doesn't know "
+                       "our node ID.")
+        h.update(c)
+        self.handshake['h'] = h.digest()
+
+    def handshake_act_two_responder(self):
+        h = Sha256Mixer(b'')
+        h.hash = self.handshake['h']
+        h.update(self.handshake['e'].public_key().serializeCompressed())
+        ee = ecdh(self.handshake['e'], self.handshake['re'])
+        t = hkdf(salt=self.chaining_key, ikm=ee.raw, info=b'')
+        assert(len(t) == 64)
+        self.chaining_key, self.temp_k2 = t[:32], t[32:]
+        c = encryptWithAD(self.temp_k2, self.nonce(0), h.digest(), b'')
+        h.update(c)
+        self.handshake['h'] = h.digest()
+        pk = self.handshake['e'].public_key().serializeCompressed()
+        m = b'\x00' + pk + c
+        return m
+
+    def handshake_act_two_initiator(self, m):
+        v, re, c = m[0], PublicKey(m[1:34]), m[34:]
+        if v != 0:
+            raise ValueError("Unsupported handshake version {}, only version "
+                             "0 is supported.".format(v))
+        self.re = re
+        h = Sha256Mixer(b'')
+        h.hash = self.handshake['h']
+        h.update(re.serializeCompressed())
+        ee = ecdh(self.handshake['e'], re)
+        self.chaining_key, self.temp_k2 = hkdf_two_keys(
+            salt=self.chaining_key, ikm=ee.raw
+        )
+        try:
+            decryptWithAD(self.temp_k2, self.nonce(0), h.digest(), c)
+        except InvalidTag:
+            ValueError("Verification of tag failed.")
+        h.update(c)
+        self.handshake['h'] = h.digest()
+
+    def handshake_act_three_initiator(self):
+        h = Sha256Mixer(b'')
+        h.hash = self.handshake['h']
+        pk = self.local_pubkey.serializeCompressed()
+        c = encryptWithAD(self.temp_k2, self.nonce(1), h.digest(), pk)
+        h.update(c)
+        se = ecdh(self.local_privkey, self.re)
+
+        self.chaining_key, self.temp_k3 = hkdf_two_keys(
+            salt=self.chaining_key, ikm=se.raw
+        )
+        t = encryptWithAD(self.temp_k3, self.nonce(0), h.digest(), b'')
+        m = b'\x00' + c + t
+        t = hkdf(salt=self.chaining_key, ikm=b'', info=b'')
+
+        self.sk, self.rk = hkdf_two_keys(salt=self.chaining_key, ikm=b'')
+        self.rn, self.sn = 0, 0
+        return m
+
+    def handshake_act_three_responder(self, m):
+        h = Sha256Mixer(b'')
+        h.hash = self.handshake['h']
+        v, c, t = m[0], m[1:50], m[50:]
+        if v != 0:
+            raise ValueError("Unsupported handshake version {}, only version "
+                             "0 is supported.".format(v))
+        rs = decryptWithAD(self.temp_k2, self.nonce(1), h.digest(), c)
+        h.update(c)
+        se = ecdh(self.handshake['e'], PublicKey(rs))
+
+        self.chaining_key, self.temp_k3 = hkdf_two_keys(
+            se.raw, self.chaining_key
+        )
+        decryptWithAD(self.temp_k3, self.nonce(0), h.digest(), t)
+        self.rn, self.sn = 0, 0
+
+        self.rk, self.sk = hkdf_two_keys(salt=self.chaining_key, ikm=b'')
+
+    def read_message(self):
+        lc = self.connection.recv(18)
+        if len(lc) != 18:
+            raise ValueError(
+                "Short read reading the message length: 18 != {}".format(
+                    len(lc))
+            )
+        length = decryptWithAD(self.rk, self.nonce(self.rn), b'', lc)
+        length, = struct.unpack("!H", length)
+        self.rn += 1
+
+        mc = self.connection.recv(length + 16)
+        if len(mc) < length + 16:
+            raise ValueError("Short read reading the message: {} != {}".format(
+                length + 16, len(lc))
+            )
+        m = decryptWithAD(self.rk, self.nonce(self.rn), b'', mc)
+        self.rn += 1
+        assert(self.rn % 2 == 0)
+        self._maybe_rotate_keys()
+        return m
+
+    def send_message(self, m):
+        length = struct.pack("!H", len(m))
+        lc = encryptWithAD(self.sk, self.nonce(self.sn), b'', length)
+        self.sn += 1
+        mc = encryptWithAD(self.sk, self.nonce(self.sn), b'', m)
+        self.sn += 1
+        self.connection.send(lc)
+        self.connection.send(mc)
+        assert(self.sn % 2 == 0)
+        self._maybe_rotate_keys()
+
+    def _maybe_rotate_keys(self):
+        if self.sn == 1000:
+            self.sck, self.sk = hkdf_two_keys(salt=self.sck, ikm=self.sk)
+            self.sn = 0
+        if self.rn == 1000:
+            self.rck, self.rk = hkdf_two_keys(salt=self.rck, ikm=self.rk)
+            self.rn = 0
+
+    def shake(self):
+        if self.is_initiator:
+            m = self.handshake_act_one_initiator()
+            self.connection.send(m)
+            m = self.connection.recv(50)
+            if len(m) != 50:
+                raise ValueError(
+                    "Short read from peer reading act2: 50 != {}".format(
+                        len(m))
+                )
+            self.handshake_act_two_initiator(m)
+            m = self.handshake_act_three_initiator()
+            self.connection.send(m)
+        else:
+            m = self.connection.recv(50)
+            if len(m) != 50:
+                raise ValueError(
+                    "Short read from peer reading act1: 50 != {}".format(
+                        len(m))
+                )
+            self.handshake_act_one_responder(m)
+            m = self.handshake_act_two_responder()
+            self.connection.send(m)
+            m = self.connection.recv(66)
+            if len(m) != 66:
+                raise ValueError(
+                    "Short read from peer reading act3: 66 != {}".format(
+                        len(m))
+                )
+            self.handshake_act_three_responder(m)
+
+        self.sck = self.chaining_key
+        self.rck = self.chaining_key
+
+
+class LightningServerSocket(socket.socket):
+    def __init__(self, local_privkey):
+        socket.socket.__init__(self)
+        self.local_privkey = local_privkey
+        self.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+
+    def accept(self):
+        print("Accepting a new socket")
+        conn, address = socket.socket.accept(self)
+        lconn = LightningConnection(
+            conn, remote_pubkey=None,
+            local_privkey=self.local_privkey,
+            is_initiator=False)
+        lconn.shake()
+        return (lconn, address)
+
+
+def connect(local_privkey, node_id, host, port=9735):
+    if isinstance(node_id, bytes) and len(node_id) == 33:
+        remote_pubkey = PublicKey(node_id)
+    elif isinstance(node_id, ec.EllipticCurvePublicKey):
+        remote_pubkey = PublicKey(node_id)
+    elif isinstance(node_id, PublicKey):
+        remote_pubkey = node_id
+    else:
+        raise ValueError(
+            "node_id must be either a 33 byte array, or a PublicKey"
+        )
+    conn = socket.create_connection((host, port))
+    lconn = LightningConnection(conn, remote_pubkey, local_privkey,
+                                is_initiator=True)
+    lconn.shake()
+    return lconn
--- a/contrib/pylightning/requirements.txt
+++ b/contrib/pylightning/requirements.txt
@ -0,0 +1,2 @@
+cryptography==2.7
+coincurve==12.0.0
--- a/contrib/pylightning/setup.py
+++ b/contrib/pylightning/setup.py
@ -6,6 +6,9 @@ import io
 with io.open('README.md', encoding='utf-8') as f:
    long_description = f.read()

+with io.open('requirements.txt', encoding='utf-8') as f:
+    requirements = [r for r in f.read().split('\n') if len(r)]
+
 setup(name='pylightning',
      version=lightning.__version__,
      description='Client library for lightningd',
@ -17,4 +20,5 @@ setup(name='pylightning',
      license='MIT',
      packages=['lightning'],
      scripts=['lightning-pay'],
-      zip_safe=True)
+      zip_safe=True,
+      install_requires=requirements)
--- a/contrib/pylightning/tests/test_wire.py
+++ b/contrib/pylightning/tests/test_wire.py
@ -0,0 +1,189 @@
+from binascii import hexlify, unhexlify
+from lightning.wire import PrivateKey, PublicKey, LightningConnection
+import socket
+from lightning import wire
+import threading
+
+
+def test_primitives():
+    raw_privkey = unhexlify('1111111111111111111111111111111111111111111111111111111111111111')
+    privkey = PrivateKey(raw_privkey)
+    pubkey = privkey.public_key()
+    assert(hexlify(pubkey.serializeCompressed()) == b'034f355bdcb7cc0af728ef3cceb9615d90684bb5b2ca5f859ab0f0b704075871aa')
+
+    # Now try with the raw constructor once more
+    pubkey = PublicKey(unhexlify(b'034f355bdcb7cc0af728ef3cceb9615d90684bb5b2ca5f859ab0f0b704075871aa'))
+    assert(hexlify(pubkey.serializeCompressed()) == b'034f355bdcb7cc0af728ef3cceb9615d90684bb5b2ca5f859ab0f0b704075871aa')
+
+
+def test_encrypt_decrypt():
+    """ Test encryptWithAD and decryptWithAD primitives
+    Taken from https://github.com/lightningnetwork/lightning-rfc/blob/master/08-transport.md#initiator-tests
+    """
+    inp = [b'e68f69b7f096d7917245f5e5cf8ae1595febe4d4644333c99f9c4a1282031c9f', b'000000000000000000000000', b'9e0e7de8bb75554f21db034633de04be41a2b8a18da7a319a03c803bf02b396c', b'']
+    inp = [unhexlify(i) for i in inp]
+    c = wire.encryptWithAD(*inp)
+    assert(hexlify(c) == b'0df6086551151f58b8afe6c195782c6a')
+
+
+def test_handshake():
+    rs_privkey = PrivateKey(unhexlify('2121212121212121212121212121212121212121212121212121212121212121'))
+    rs_pubkey = rs_privkey.public_key()
+    assert(hexlify(rs_pubkey.serializeCompressed()) == b'028d7500dd4c12685d1f568b4c2b5048e8534b873319f3a8daa612b469132ec7f7')
+
+    ls_privkey = PrivateKey(unhexlify('1111111111111111111111111111111111111111111111111111111111111111'))
+    ls_pubkey = ls_privkey.public_key()
+    assert(hexlify(ls_pubkey.serializeCompressed()) == b'034f355bdcb7cc0af728ef3cceb9615d90684bb5b2ca5f859ab0f0b704075871aa')
+
+    c1, c2 = socket.socketpair()
+
+    lc1 = LightningConnection(c1, rs_pubkey, ls_privkey, is_initiator=True)
+    lc2 = LightningConnection(c2, ls_pubkey, rs_privkey, is_initiator=False)
+
+    # Override the generated ephemeral key for the test:
+    lc1.handshake['e'] = PrivateKey(unhexlify('1212121212121212121212121212121212121212121212121212121212121212'))
+    lc2.handshake['e'] = PrivateKey(unhexlify(b'2222222222222222222222222222222222222222222222222222222222222222'))
+    assert(hexlify(lc1.handshake['e'].public_key().serializeCompressed()) == b'036360e856310ce5d294e8be33fc807077dc56ac80d95d9cd4ddbd21325eff73f7')
+
+    assert(hexlify(lc1.handshake['h']) == b'8401b3fdcaaa710b5405400536a3d5fd7792fe8e7fe29cd8b687216fe323ecbd')
+    assert(lc1.handshake['h'] == lc2.handshake['h'])
+    m = lc1.handshake_act_one_initiator()
+    assert(hexlify(m) == b'00036360e856310ce5d294e8be33fc807077dc56ac80d95d9cd4ddbd21325eff73f70df6086551151f58b8afe6c195782c6a')
+
+    lc2.handshake_act_one_responder(m)
+    assert(hexlify(lc1.handshake['h']) == b'9d1ffbb639e7e20021d9259491dc7b160aab270fb1339ef135053f6f2cebe9ce')
+    assert(hexlify(lc1.handshake['h']) == hexlify(lc2.handshake['h']))
+
+    assert(hexlify(lc1.chaining_key) == b'b61ec1191326fa240decc9564369dbb3ae2b34341d1e11ad64ed89f89180582f')
+    assert(hexlify(lc2.chaining_key) == b'b61ec1191326fa240decc9564369dbb3ae2b34341d1e11ad64ed89f89180582f')
+
+    m = lc2.handshake_act_two_responder()
+    assert(hexlify(m) == b'0002466d7fcae563e5cb09a0d1870bb580344804617879a14949cf22285f1bae3f276e2470b93aac583c9ef6eafca3f730ae')
+    assert(hexlify(lc2.handshake['h']) == b'90578e247e98674e661013da3c5c1ca6a8c8f48c90b485c0dfa1494e23d56d72')
+
+    lc1.handshake_act_two_initiator(m)
+    assert(hexlify(lc1.handshake['h']) == b'90578e247e98674e661013da3c5c1ca6a8c8f48c90b485c0dfa1494e23d56d72')
+
+    assert(hexlify(lc1.chaining_key) == b'e89d31033a1b6bf68c07d22e08ea4d7884646c4b60a9528598ccb4ee2c8f56ba')
+    assert(hexlify(lc2.chaining_key) == b'e89d31033a1b6bf68c07d22e08ea4d7884646c4b60a9528598ccb4ee2c8f56ba')
+
+    m = lc1.handshake_act_three_initiator()
+    assert(hexlify(m) == b'00b9e3a702e93e3a9948c2ed6e5fd7590a6e1c3a0344cfc9d5b57357049aa22355361aa02e55a8fc28fef5bd6d71ad0c38228dc68b1c466263b47fdf31e560e139ba')
+    assert(hexlify(lc1.sk) == b'969ab31b4d288cedf6218839b27a3e2140827047f2c0f01bf5c04435d43511a9')
+    assert(hexlify(lc1.rk) == b'bb9020b8965f4df047e07f955f3c4b88418984aadc5cdb35096b9ea8fa5c3442')
+    lc2.handshake_act_three_responder(m)
+
+    assert(lc1.rk == lc2.sk)
+    assert(lc1.sk == lc2.rk)
+    assert(lc1.sn == lc2.rn)
+    assert(lc1.rn == lc2.sn)
+    assert(hexlify(lc2.rk) == b'969ab31b4d288cedf6218839b27a3e2140827047f2c0f01bf5c04435d43511a9')
+    assert(hexlify(lc2.sk) == b'bb9020b8965f4df047e07f955f3c4b88418984aadc5cdb35096b9ea8fa5c3442')
+
+
+def test_shake():
+    rs_privkey = PrivateKey(unhexlify('2121212121212121212121212121212121212121212121212121212121212121'))
+    rs_pubkey = rs_privkey.public_key()
+    assert(hexlify(rs_pubkey.serializeCompressed()) == b'028d7500dd4c12685d1f568b4c2b5048e8534b873319f3a8daa612b469132ec7f7')
+
+    ls_privkey = PrivateKey(unhexlify('1111111111111111111111111111111111111111111111111111111111111111'))
+    ls_pubkey = ls_privkey.public_key()
+    assert(hexlify(ls_pubkey.serializeCompressed()) == b'034f355bdcb7cc0af728ef3cceb9615d90684bb5b2ca5f859ab0f0b704075871aa')
+
+    c1, c2 = socket.socketpair()
+
+    lc1 = LightningConnection(c1, rs_pubkey, ls_privkey, is_initiator=True)
+    lc2 = LightningConnection(c2, ls_pubkey, rs_privkey, is_initiator=False)
+
+    t = threading.Thread(target=lc2.shake)
+    t.start()
+    lc1.shake()
+    t.join()
+
+    assert(lc1.rk == lc2.sk)
+    assert(lc1.sk == lc2.rk)
+    assert(lc1.sn == lc2.rn)
+    assert(lc1.rn == lc2.sn)
+
+
+def test_read_key_rotation():
+    ls_privkey = PrivateKey(unhexlify('1111111111111111111111111111111111111111111111111111111111111111'))
+    rs_privkey = PrivateKey(unhexlify('2121212121212121212121212121212121212121212121212121212121212121'))
+    rs_pubkey = rs_privkey.public_key()
+    c1, c2 = socket.socketpair()
+    lc = LightningConnection(c1, rs_pubkey, ls_privkey, is_initiator=True)
+    # ck=0x919219dbb2920afa8db80f9a51787a840bcf111ed8d588caf9ab4be716e42b01
+    # sk=0x969ab31b4d288cedf6218839b27a3e2140827047f2c0f01bf5c04435d43511a9
+    # rk=0xbb9020b8965f4df047e07f955f3c4b88418984aadc5cdb35096b9ea8fa5c3442
+    lc.chaining_key = unhexlify(b'919219dbb2920afa8db80f9a51787a840bcf111ed8d588caf9ab4be716e42b01')
+    lc.sk = unhexlify(b'969ab31b4d288cedf6218839b27a3e2140827047f2c0f01bf5c04435d43511a9')
+    lc.rk = unhexlify(b'bb9020b8965f4df047e07f955f3c4b88418984aadc5cdb35096b9ea8fa5c3442')
+    lc.sn, lc.rn = 0, 0
+    lc.sck, lc.rck = lc.chaining_key, lc.chaining_key
+
+    msg = unhexlify(b'68656c6c6f')
+    lc.send_message(msg)
+    m = c2.recv(18 + 21)
+    assert(hexlify(m) == b'cf2b30ddf0cf3f80e7c35a6e6730b59fe802473180f396d88a8fb0db8cbcf25d2f214cf9ea1d95')
+
+    # Send 498 more messages, to get just below the switch threshold
+    for i in range(0, 498):
+        lc.send_message(msg)
+        m = c2.recv(18 + 21)
+    # Check the last message against the test vector
+    assert(hexlify(lc.sk) == b'969ab31b4d288cedf6218839b27a3e2140827047f2c0f01bf5c04435d43511a9')
+
+    # This next message triggers the rotation:
+    lc.send_message(msg)
+    m = c2.recv(18 + 21)
+
+    # Now try to send with the new keys:
+    lc.send_message(msg)
+    m = c2.recv(18 + 21)
+    assert(hexlify(m) == b'178cb9d7387190fa34db9c2d50027d21793c9bc2d40b1e14dcf30ebeeeb220f48364f7a4c68bf8')
+
+    lc.send_message(msg)
+    m = c2.recv(18 + 21)
+    assert(hexlify(m) == b'1b186c57d44eb6de4c057c49940d79bb838a145cb528d6e8fd26dbe50a60ca2c104b56b60e45bd')
+
+    for i in range(0, 498):
+        lc.send_message(msg)
+        m = c2.recv(18 + 21)
+
+    lc.send_message(msg)
+    m = c2.recv(18 + 21)
+    assert(hexlify(m) == b'4a2f3cc3b5e78ddb83dcb426d9863d9d9a723b0337c89dd0b005d89f8d3c05c52b76b29b740f09')
+
+    lc.send_message(msg)
+    m = c2.recv(18 + 21)
+    assert(hexlify(m) == b'2ecd8c8a5629d0d02ab457a0fdd0f7b90a192cd46be5ecb6ca570bfc5e268338b1a16cf4ef2d36')
+
+
+def test_listen_connect():
+    """Roundtrip test using the public constructors.
+    """
+    n1_privkey = PrivateKey(unhexlify(b'1111111111111111111111111111111111111111111111111111111111111111'))
+    n2_privkey = PrivateKey(unhexlify('2121212121212121212121212121212121212121212121212121212121212121'))
+
+    lss = wire.LightningServerSocket(n2_privkey)
+    lss.bind(('0.0.0.0', 1234))
+    lss.listen()
+    port = lss.getsockname()[1]
+    print(port)
+
+    def connect():
+        lc = wire.connect(n1_privkey, n2_privkey.public_key(), '127.0.0.1', port)
+        lc.send_message(b'hello')
+        m = lc.read_message()
+        assert(m == b'world')
+
+    t = threading.Thread(target=connect)
+    t.daemon = True
+    t.start()
+
+    c, _ = lss.accept()
+    m = c.read_message()
+    assert(m == b'hello')
+    c.send_message(b'world')
+
+    t.join()