def make_fragment(message_id, fragment_number, last_fragment, payload,
payload_limit):
if fragment_number > 0b0011_1111:
raise ValueError("Too many fragments needed for this payload.")
if not payload and message_id != DUMMY_FRAG_ID:
raise ValueError("No more fragments left to generate.")
frag_byte = fragment_number
if last_fragment:
frag_byte |= FragmentGenerator.LAST_FRAG_FLAG
if len(payload) < payload_limit:
frag_byte |= FragmentGenerator.PADDING_FLAG
padding_bytes, padding_len = padding_length_to_bytes(payload_limit -
len(payload))
else:
padding_len = 0
padding_bytes = bytes()
fragment = i2b(message_id, FRAG_ID_SIZE) + i2b(frag_byte, FRAG_FLAG_SIZE)
fragment += padding_bytes
fragment += payload[:payload_limit] + get_random_bytes(padding_len)
return fragment
def parse_channel_init(self, channel_init, priv_comp):
"""Takes an already decrypted channel init message and reads the key.
"""
self.last_interaction = time()
msg_ctr, channel_init = cut(channel_init, CTR_PREFIX_LEN)
self.request_replay_detector.check_replay_window(b2i(msg_ctr))
sym_key, _, channel_init = process(priv_comp, channel_init)
if self.key is not None:
assert self.key == sym_key
self.initialized = True
else:
self.key = sym_key
print(self, "Init", "->", len(channel_init))
channel_init = msg_ctr + channel_init
# we add an empty ctr prefix, because the link encryption expects there
# to be one, even though the channel init wasn't sym encrypted
# todo look at this one again
packet = CHAN_INIT_MSG_FLAG + i2b(self.out_chan_id, CHAN_ID_SIZE) + channel_init
ChannelMid.requests.append(packet)
def __init__(self, src_addr, dest_addr, pub_comps):
self.src_addr = src_addr
self.dest_addr = dest_addr
self.chan_id = ChannelEntry.random_channel()
self.b_chan_id = i2b(self.chan_id, CHAN_ID_SIZE)
self.pub_comps = pub_comps
print(self, "New Channel", self.dest_addr)
ChannelEntry.table[self.chan_id] = self
self.sym_keys = []
self.request_counter = Counter(CHANNEL_CTR_START)
self.replay_detector = ReplayDetector(start=CHANNEL_CTR_START)
for _ in self.pub_comps:
self.sym_keys.append(gen_sym_key())
self.packets = []
self.mix_msg_store = MixMessageStore()
self.last_interaction = time()
self.allowed_to_send = False
def forward_response(self, response):
self.last_interaction = time()
# cut the padding off
response, _ = cut(response, -CTR_MODE_PADDING)
msg_type, response = cut(response, MSG_TYPE_FLAG_LEN)
msg_ctr, _ = cut(response, CTR_PREFIX_LEN)
# todo find better way
if msg_ctr != bytes(CTR_PREFIX_LEN):
self.response_replay_detector.check_replay_window(b2i(msg_ctr))
self.response_counter.next()
cipher = ctr_cipher(self.key, int(self.response_counter))
forward_msg = cipher.encrypt(response)
print(self, "Data", "<-", len(forward_msg))
response = msg_type + i2b(self.in_chan_id, CHAN_ID_SIZE) + bytes(self.response_counter) + forward_msg
ChannelMid.responses.append(response)
def __init__(self, csv_row, port):
self.packet_id = int(csv_row[PACKET_ID_INDEX])
self.timestamp = float(csv_row[TIMESTAMP_INDEX])
self.port = i2b(port, PORT_LEN)
self.payload_len = int(csv_row[LENGTH_INDEX])
self.payload_len -= ETHERNET_STACK_OVERHEAD
def test_replay_detection_too_small():
encryptor = LinkEncryptor(link_key)
decryptor = LinkDecryptor(link_key)
first_encrypted = encryptor.encrypt(msg_type + i2b(chan_id, CHAN_ID_SIZE) +
msg_ctr + payload)
first_link_counter = encryptor.counter
for _ in range(REPLAY_WINDOW_SIZE + 1):
encrypted = encryptor.encrypt(msg_type + i2b(chan_id, CHAN_ID_SIZE) +
msg_ctr + payload)
decryptor.decrypt(encrypted)
assert first_link_counter not in decryptor.replay_detector.replay_window
try:
decryptor.decrypt(first_encrypted)
except ReplayDetectedError:
assert True
return
assert False
def test_link_encryption():
encryptor = LinkEncryptor(link_key)
decryptor = LinkDecryptor(link_key)
encrypted = encryptor.encrypt(msg_type + i2b(chan_id, CHAN_ID_SIZE) +
msg_ctr + payload)
chan_id2, msg_ctr2, payload2, msg_type2 = decryptor.decrypt(encrypted)
assert int(encryptor.counter) in decryptor.replay_detector
assert chan_id == chan_id2
assert msg_ctr == msg_ctr2
assert payload == payload2
assert msg_type == msg_type2
def recv_response(self, response):
self.last_interaction = time()
"""Turns the response into a MixMessage and saves its fragments for
later sending.
"""
frag_gen = FragmentGenerator(response)
while frag_gen:
print(self, "Data", "<-", len(frag_gen.udp_payload))
fragment = frag_gen.get_data_fragment()
packet = fragment + get_random_bytes(MIX_COUNT * CTR_PREFIX_LEN)
ChannelExit.to_mix.append(DATA_MSG_FLAG + i2b(self.in_chan_id, CHAN_ID_SIZE) + packet)
def _get_init_message(self):
self.request_counter.next()
ip, port = self.dest_addr
destination = ip2b(ip) + i2b(port, PORT_LEN)
fragment = self._get_init_fragment()
channel_init = gen_init_msg(self.pub_comps, self.sym_keys, destination + fragment)
print(self, "Init", "->", len(channel_init))
# we send a counter value with init messages for channel replay detection only
return CHAN_INIT_MSG_FLAG + self.b_chan_id + bytes(self.request_counter) + channel_init
def test_replay_detection_already_seen():
encryptor = LinkEncryptor(link_key)
decryptor = LinkDecryptor(link_key)
encrypted = encryptor.encrypt(msg_type + i2b(chan_id, CHAN_ID_SIZE) +
msg_ctr + payload)
decryptor.decrypt(encrypted)
try:
decryptor.decrypt(encrypted)
except ReplayDetectedError:
assert True
return
assert False
def test_encrypt_fragment():
channel = ChannelEntry(src_addr, dest_addr, public_keys)
sym_key = gen_sym_key()
channel.sym_keys = [sym_key] * MIX_COUNT
fragment = FragmentGenerator(bytes(100)).get_data_fragment()
packet1 = channel._encrypt_fragment(fragment)
packet2 = fragment
counter = 1
for _ in range(MIX_COUNT):
cipher = ctr_cipher(sym_key, counter)
packet2 = i2b(counter, CTR_PREFIX_LEN) + cipher.encrypt(packet2)
assert packet1 == packet2
def forward_request(self, request):
"""Takes a mix fragment, already stripped of the channel id."""
self.last_interaction = time()
ctr, cipher_text = cut(request, CTR_PREFIX_LEN)
ctr = b2i(ctr)
self.request_replay_detector.check_replay_window(ctr)
cipher = ctr_cipher(self.key, ctr)
forward_msg = cipher.decrypt(cipher_text) + get_random_bytes(CTR_MODE_PADDING)
print(self, "Data", "->", len(forward_msg) - CTR_PREFIX_LEN)
ChannelMid.requests.append(DATA_MSG_FLAG + i2b(self.out_chan_id, CHAN_ID_SIZE) + forward_msg)
timed_out = check_for_timed_out_channels(ChannelMid.table_in)
for in_id in timed_out:
out_id = ChannelMid.table_in[in_id].out_chan_id
del ChannelMid.table_in[in_id]
del ChannelMid.table_out[out_id]
ip, port = "127.0.0.1", 45000
entry_addr = ("127.0.0.1", 20000)
if len(argv) > 1:
to_send = int(argv[1])
else:
to_send = -1
sock = socket(AF_INET, UDP)
start = time()
packets = 1
while to_send != 0:
msg_size = randrange(MIN_MSG_SIZE, MAX_MSG_SIZE)
pack_id = i2b(packets, 4)
try:
sock.sendto(
ip2b(ip) + i2b(port, 2) + pack_id + bytes(msg_size - 4),
entry_addr)
except OSError:
continue
to_send -= 1
sleep(1 / 20.0)
print("Sent", packets, "packets in", time() - start, "seconds.")
def send_chan_confirm(self):
print(self, "Init", "<-", "len:", DATA_PACKET_SIZE)
ChannelExit.to_mix.append(CHAN_CONFIRM_MSG_FLAG + i2b(self.in_chan_id, CHAN_ID_SIZE) + bytes(CTR_PREFIX_LEN) + get_random_bytes(DATA_PACKET_SIZE))
def header(ip, port):
return ip2b(ip) + i2b(port, 2)
def __bytes__(self):
return i2b(self.current_value, CTR_PREFIX_LEN)
def get_bytes(self):
return Packet.ip + self.port + i2b(self.packet_id, 4) + bytes(
self.payload_len)
