Add reference implementation for ntor v3.

src/test/ntor_v3_ref.py

@@ -0,0 +1,308 @@
+#!/usr/bin/python
+
+import binascii
+import hashlib
+import os
+import struct
+
+import donna25519
+from Crypto.Cipher import AES
+from Crypto.Util import Counter
+
+# Define basic wrappers.
+
+DIGEST_LEN = 32
+ENC_KEY_LEN = 32
+PUB_KEY_LEN = 32
+SEC_KEY_LEN = 32
+IDENTITY_LEN = 32
+
+def sha3_256(s):
+    d = hashlib.sha3_256(s).digest()
+    assert len(d) == DIGEST_LEN
+    return d
+
+def shake_256(s):
+    # Note: In reality, you wouldn't want to generate more bytes than needed.
+    MAX_KEY_BYTES = 1024
+    return hashlib.shake_256(s).digest(MAX_KEY_BYTES)
+
+def curve25519(pk, sk):
+    assert len(pk) == PUB_KEY_LEN
+    assert len(sk) == SEC_KEY_LEN
+    private = donna25519.PrivateKey.load(sk)
+    public = donna25519.PublicKey(pk)
+    return private.do_exchange(public)
+
+def keygen():
+    private = donna25519.PrivateKey()
+    public = private.get_public()
+    return (private.private, public.public)
+
+def aes256_ctr(k, s):
+    assert len(k) == ENC_KEY_LEN
+    cipher = AES.new(k, AES.MODE_CTR, counter=Counter.new(128, initial_value=0))
+    return cipher.encrypt(s)
+
+# Byte-oriented helper.  We use this for decoding keystreams and messages.
+
+class ByteSeq:
+    def __init__(self, data):
+        self.data = data
+
+    def take(self, n):
+        assert n <= len(self.data)
+        result = self.data[:n]
+        self.data = self.data[n:]
+        return result
+
+    def exhausted(self):
+        return len(self.data) == 0
+
+    def remaining(self):
+        return len(self.data)
+
+# Low-level functions
+
+MAC_KEY_LEN = 32
+MAC_LEN = DIGEST_LEN
+
+hash_func = sha3_256
+
+def encapsulate(s):
+    """encapsulate `s` with a length prefix.
+
+       We use this whenever we need to avoid message ambiguities in
+       cryptographic inputs.
+    """
+    assert len(s) <= 0xffffffff
+    header = b"\0\0\0\0" + struct.pack("!L", len(s))
+    assert len(header) == 8
+    return header + s
+
+def h(s, tweak):
+    return hash_func(encapsulate(tweak) + s)
+
+def mac(s, key, tweak):
+    return hash_func(encapsulate(tweak) + encapsulate(key) + s)
+
+def kdf(s, tweak):
+    data = shake_256(encapsulate(tweak) + s)
+    return ByteSeq(data)
+
+def enc(s, k):
+    return aes256_ctr(k, s)
+
+# Tweaked wrappers
+
+PROTOID = b"ntor3-curve25519-sha3_256-1"
+T_KDF_PHASE1 = PROTOID + b":kdf_phase1"
+T_MAC_PHASE1 = PROTOID + b":msg_mac"
+T_KDF_FINAL = PROTOID + b":kdf_final"
+T_KEY_SEED = PROTOID + b":key_seed"
+T_VERIFY = PROTOID + b":verify"
+T_AUTH = PROTOID + b":auth_final"
+
+def kdf_phase1(s):
+    return kdf(s, T_KDF_PHASE1)
+
+def kdf_final(s):
+    return kdf(s, T_KDF_FINAL)
+
+def mac_phase1(s, key):
+    return mac(s, key, T_MAC_PHASE1)
+
+def h_key_seed(s):
+    return h(s, T_KEY_SEED)
+
+def h_verify(s):
+    return h(s, T_VERIFY)
+
+def h_auth(s):
+    return h(s, T_AUTH)
+
+# Handshake.
+
+def client_phase1(msg, verification, B, ID):
+    assert len(B) == PUB_KEY_LEN
+    assert len(ID) == IDENTITY_LEN
+
+    (x,X) = keygen()
+    p(["x", "X"], locals())
+    p(["msg", "verification"], locals())
+    Bx = curve25519(B, x)
+    secret_input_phase1 = Bx + ID + X + B + PROTOID + encapsulate(verification)
+
+    phase1_keys = kdf_phase1(secret_input_phase1)
+    enc_key = phase1_keys.take(ENC_KEY_LEN)
+    mac_key = phase1_keys.take(MAC_KEY_LEN)
+    p(["enc_key", "mac_key"], locals())
+
+    msg_0 = ID + B + X + enc(msg, enc_key)
+    mac = mac_phase1(msg_0, mac_key)
+    p(["mac"], locals())
+
+    client_handshake = msg_0 + mac
+    state = dict(x=x, X=X, B=B, ID=ID, Bx=Bx, mac=mac, verification=verification)
+
+    p(["client_handshake"], locals())
+
+    return (client_handshake, state)
+
+# server.
+
+class Reject(Exception):
+    pass
+
+def server_part1(cmsg, verification, b, B, ID):
+    assert len(B) == PUB_KEY_LEN
+    assert len(ID) == IDENTITY_LEN
+    assert len(b) == SEC_KEY_LEN
+
+    if len(cmsg) < (IDENTITY_LEN + PUB_KEY_LEN * 2 + MAC_LEN):
+        raise Reject()
+
+    mac_covered_portion = cmsg[0:-MAC_LEN]
+    cmsg = ByteSeq(cmsg)
+    cmsg_id = cmsg.take(IDENTITY_LEN)
+    cmsg_B = cmsg.take(PUB_KEY_LEN)
+    cmsg_X = cmsg.take(PUB_KEY_LEN)
+    cmsg_msg = cmsg.take(cmsg.remaining() - MAC_LEN)
+    cmsg_mac = cmsg.take(MAC_LEN)
+
+    assert cmsg.exhausted()
+
+    # XXXX for real purposes, you would use constant-time checks here
+    if cmsg_id != ID or cmsg_B != B:
+        raise Reject()
+
+    Xb = curve25519(cmsg_X, b)
+    secret_input_phase1 = Xb + ID + cmsg_X + B + PROTOID + encapsulate(verification)
+
+    phase1_keys = kdf_phase1(secret_input_phase1)
+    enc_key = phase1_keys.take(ENC_KEY_LEN)
+    mac_key = phase1_keys.take(MAC_KEY_LEN)
+
+    mac_received = mac_phase1(mac_covered_portion, mac_key)
+    if mac_received != cmsg_mac:
+        raise Reject()
+
+    client_msg = enc(cmsg_msg, enc_key)
+    state = dict(
+        b=b,
+        B=B,
+        X=cmsg_X,
+        mac_received=mac_received,
+        Xb=Xb,
+        ID=ID,
+        verification=verification)
+
+    return (client_msg, state)
+
+def server_part2(state, server_msg):
+    X = state['X']
+    Xb = state['Xb']
+    B = state['B']
+    b = state['b']
+    ID = state['ID']
+    mac_received = state['mac_received']
+    verification = state['verification']
+
+    p(["server_msg"], locals())
+    
+    (y,Y) = keygen()
+    p(["y", "Y"], locals())
+    Xy = curve25519(X, y)
+
+    secret_input = Xy + Xb + ID + B + X + Y + PROTOID + encapsulate(verification)
+    key_seed = h_key_seed(secret_input)
+    verify = h_verify(secret_input)
+    p(["key_seed", "verify"], locals())
+
+    keys = kdf_final(key_seed)
+    server_enc_key = keys.take(ENC_KEY_LEN)
+    p(["server_enc_key"], locals())
+
+    smsg_msg = enc(server_msg, server_enc_key)
+
+    auth_input = verify + ID + B + Y + X + mac_received + encapsulate(smsg_msg) + PROTOID + b"Server"
+
+    auth = h_auth(auth_input)
+    server_handshake = Y + auth + smsg_msg
+    p(["auth", "server_handshake"], locals())
+
+    return (server_handshake, keys)
+
+def client_phase2(state, smsg):
+    x = state['x']
+    X = state['X']
+    B = state['B']
+    ID = state['ID']
+    Bx = state['Bx']
+    mac_sent = state['mac']
+    verification = state['verification']
+
+    if len(smsg) < PUB_KEY_LEN + DIGEST_LEN:
+        raise Reject()
+
+    smsg = ByteSeq(smsg)
+    Y = smsg.take(PUB_KEY_LEN)
+    auth_received = smsg.take(DIGEST_LEN)
+    server_msg = smsg.take(smsg.remaining())
+
+    Yx = curve25519(Y,x)
+
+    secret_input = Yx + Bx + ID + B + X + Y + PROTOID + encapsulate(verification)
+    key_seed = h_key_seed(secret_input)
+    verify = h_verify(secret_input)
+
+    auth_input = verify + ID + B + Y + X + mac_sent + encapsulate(server_msg) + PROTOID + b"Server"
+
+    auth = h_auth(auth_input)
+    if auth != auth_received:
+        raise Reject()
+
+    keys = kdf_final(key_seed)
+    enc_key = keys.take(ENC_KEY_LEN)
+
+    server_msg_decrypted = enc(server_msg, enc_key)
+
+    return (keys, server_msg_decrypted)
+
+def p(varnames, localvars):
+    for v in varnames:
+        label = v
+        val = localvars[label]
+        print('{} = "{}"'.format(label, binascii.b2a_hex(val).decode("ascii")))
+
+def test():
+    (b,B) = keygen()
+    ID = os.urandom(IDENTITY_LEN)
+
+    p(["b", "B", "ID"], locals())
+
+    print("# ============")
+    (c_handshake, c_state) = client_phase1(b"hello world", b"xyzzy", B, ID)
+
+    print("# ============")
+
+    (c_msg_got, s_state) = server_part1(c_handshake, b"xyzzy", b, B, ID)
+
+    #print(repr(c_msg_got))
+
+    (s_handshake, s_keys) = server_part2(s_state, b"Hola Mundo")
+
+    print("# ============")
+
+    (c_keys, s_msg_got) = client_phase2(c_state, s_handshake)
+
+    #print(repr(s_msg_got))
+
+    c_keys_256 = c_keys.take(256)
+    p(["c_keys_256"], locals())
+
+    assert (c_keys_256 == s_keys.take(256))
+
+
+if __name__ == '__main__':
+    test()