def parse_fragment(fragment):
msg_id, frag_byte, rest = cut(fragment, FRAG_ID_SIZE, FRAG_FLAG_SIZE)
i_frag_byte = b2i(frag_byte)
fragment_id = i_frag_byte & 0b0011_1111
is_last = (
i_frag_byte
& FragmentGenerator.LAST_FRAG_FLAG) == FragmentGenerator.LAST_FRAG_FLAG
payload_len = len(rest)
has_padding = (
i_frag_byte
& FragmentGenerator.PADDING_FLAG) == FragmentGenerator.PADDING_FLAG
if has_padding:
padding_len, padding_bytes = bytes_to_padding_length(rest)
payload_len -= (padding_len + padding_bytes)
_, payload, _ = cut(rest, padding_bytes, payload_len)
else:
payload = rest
return b2i(msg_id), is_last, fragment_id, payload
def test_get_data_fragment():
udp_payload = get_random_bytes(DATA_FRAG_PAYLOAD_SIZE)
f = FragmentGenerator(udp_payload)
fragment = f.get_data_fragment()
_, frag_byte, payload = cut(fragment, FRAG_ID_SIZE, FRAG_FLAG_SIZE)
assert b2i(frag_byte) & FragmentGenerator.LAST_FRAG_FLAG
assert b2i(frag_byte) == 0b0100_0000
assert payload[0:DATA_FRAG_PAYLOAD_SIZE] == udp_payload
assert len(
fragment) == DATA_FRAG_PAYLOAD_SIZE + FRAG_ID_SIZE + FRAG_FLAG_SIZE
def parse_channel_init(self, channel_init):
self.last_interaction = time()
_, _, payload = cut_init_message(channel_init)
ip, port, fragment = cut(payload, IPV4_LEN, PORT_LEN)
ip = b2ip(ip)
port = b2i(port)
self.dest_addr = (ip, port)
try:
self.out_sock.connect(self.dest_addr)
except OSError:
# couldn't connect, maybe not a channel init message?
print("Couldn't connect to destination. Dropped message.")
self.out_sock.close()
del ChannelExit.table[self.in_chan_id]
return
ChannelExit.sock_sel.register(self.out_sock, EVENT_READ, data=self)
print(self, "Init", "->", len(channel_init))
self.recv_request(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 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 decrypt(self, cipher_text):
b_link_ctr, header, mac, fragment = cut(cipher_text, CTR_PREFIX_LEN,
LINK_HEADER_LEN, GCM_MAC_LEN)
link_ctr = b2i(b_link_ctr)
cipher = gcm_cipher(self.key, link_ctr)
plain_header = cipher.decrypt_and_verify(header, mac)
chan_id, msg_ctr, msg_type, _ = cut(plain_header, CHAN_ID_SIZE,
CTR_PREFIX_LEN, MSG_TYPE_FLAG_LEN)
self.replay_detector.check_replay_window(link_ctr)
return b2i(chan_id), msg_ctr, fragment, msg_type
def test_get_data_fragment_with_padding():
udp_payload = get_random_bytes(DATA_FRAG_PAYLOAD_SIZE - 1)
f = FragmentGenerator(udp_payload)
fragment = f.get_data_fragment()
_, frag_byte, _, payload = cut(fragment, FRAG_ID_SIZE, FRAG_FLAG_SIZE, 1)
assert b2i(frag_byte) & FragmentGenerator.LAST_FRAG_FLAG
assert b2i(frag_byte) & FragmentGenerator.PADDING_FLAG
assert b2i(frag_byte) == 0b1100_0000
assert payload[0:DATA_FRAG_PAYLOAD_SIZE - 1] == udp_payload
assert len(
fragment) == DATA_FRAG_PAYLOAD_SIZE + FRAG_ID_SIZE + FRAG_FLAG_SIZE
udp_payload = get_random_bytes(1)
f = FragmentGenerator(udp_payload)
fragment = f.get_data_fragment()
_, frag_byte, _, payload = cut(fragment, FRAG_ID_SIZE, FRAG_FLAG_SIZE, 2)
assert b2i(frag_byte) & FragmentGenerator.LAST_FRAG_FLAG
assert b2i(frag_byte) & FragmentGenerator.PADDING_FLAG
assert b2i(frag_byte) == 0b1100_0000
assert payload[0:1] == udp_payload
assert len(
fragment) == DATA_FRAG_PAYLOAD_SIZE + FRAG_ID_SIZE + FRAG_FLAG_SIZE
def _decrypt_fragment(self, fragment):
ctr = 0
for key in self.sym_keys:
ctr, cipher_text = cut(fragment, CTR_PREFIX_LEN)
ctr = b2i(ctr)
cipher = ctr_cipher(key, ctr)
fragment = cipher.decrypt(cipher_text)
self.replay_detector.check_replay_window(ctr)
return fragment
def handle_client_request(self, request, src_addr):
"""Takes a message and the source address it came from. The destination
header is cut off, parsed and mapped to a channel. Then the payload is
separated into mix fragments and sent out with the channel id in front.
"""
dest_ip, dest_port, payload = cut(request, IPV4_LEN, PORT_LEN)
dest_addr = (b2ip(dest_ip), b2i(dest_port))
if (src_addr, dest_addr) not in self.ips2id:
channel = self.make_new_channel(src_addr, dest_addr)
else:
try:
channel_id = self.ips2id[src_addr, dest_addr]
channel = ChannelEntry.table[channel_id]
except KeyError:
del self.ips2id[src_addr, dest_addr]
channel = self.make_new_channel(src_addr, dest_addr)
# add fragments to internal packet list
channel.request(payload)
def test_decrypt_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()
fragment = channel._encrypt_fragment(fragment)
packet1 = channel._decrypt_fragment(fragment)
for _ in range(MIX_COUNT):
msg_ctr, fragment = cut(fragment, CTR_PREFIX_LEN)
cipher = ctr_cipher(sym_key, b2i(msg_ctr))
fragment = cipher.decrypt(fragment)
packet2 = fragment
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]
"Receives data on the specified ip:port using UDP and prints it on stdout."
)
parser.add_argument("ip:port",
help="IP and Port pair to listen for datagrams on.")
BUFFER_SIZE = 65535
if __name__ == "__main__":
args = parser.parse_args()
ip, port = getattr(args, "ip:port").split(":")
port = int(port)
sock = socket(AF_INET, UDP)
sock.bind((ip, port))
packets = 0
start_time = None
while True:
try:
data, addr = sock.recvfrom(BUFFER_SIZE)
packets += 1
print(str(b2i(data[0:4])).rjust(7), "{:.9f}".format(time()))
except KeyboardInterrupt:
break
output_file = argv[1]
for port_number in argv[2:]:
listener_socket = socket(AF_INET, SOCK_DGRAM)
listener_socket.bind(("127.0.0.1", int(port_number)))
socket_selector.register(listener_socket, EVENT_READ)
def set_killed(signal, stackframe):
global killed
killed = True
signal(SIGTERM, set_killed)
killed = False
with open(output_file, "w") as f:
while not killed:
events = socket_selector.select(timeout=2)
for key, _ in events:
sock = key.fileobj
data = sock.recv(UDP_MTU)
f.write("{} {:.9f}\n".format(str(b2i(data[0:4])).rjust(7), time()))
f.flush()