commit a36391f9c0ca4d4206a1335f8ef80d6a135971de Author: Nick Mathewson nickm@torproject.org Date: Thu Aug 26 12:07:09 2021 -0400

Add reference implementation for ntor v3. --- src/test/ntor_v3_ref.py | 308 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 308 insertions(+)

diff --git a/src/test/ntor_v3_ref.py b/src/test/ntor_v3_ref.py new file mode 100755 index 0000000000..28bc077105 --- /dev/null +++ b/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()