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#!/usr/bin/env python3
"""
Follow/Split TCP streams with scapy.
"""
import argparse
import scapy
import scapy.all
import sys
import time
import TCPStream
import TCPStreamExtractor
MAX_BYTES_PER_PACKET = 2
class TCPSplitStreamException(Exception):
def __init__(self, msg):
super(Exception, self).__init__(msg)
class TCPSplitData(object):
def __init__(self, pkt_timestamp, pkt_direction, pkt_payload):
self.time = pkt_timestamp
self.direction = pkt_direction # False if src->dst, True otherwise
self.payload = pkt_payload
class TCPSplitStream(object):
def __init__(self, tcp_stream: TCPStream.TCPStream):
if not isinstance(tcp_stream, TCPStream.TCPStream):
raise TypeError('Got type ' + str(type(tcp_stream)) +
', expected ' + str(TCPStream.TCPStream))
self.stream = tcp_stream
self.ordered_pkts = self.stream.get_order_pkts()
self.ip2dst = scapy.all.IP(src = self.stream.src, dst = self.stream.dst)
self.ip2src = scapy.all.IP(src = self.stream.dst, dst = self.stream.src)
if self.stream.tcp_state.syn_seen is True:
self.seq = self.ordered_pkts[0][scapy.all.TCP].seq # TCP-SYN
self.ack = self.ordered_pkts[1][scapy.all.TCP].seq # TCP-SYN-ACK
else:
self.seq = self.ordered_pkts[0][scapy.all.TCP].seq
self.ack = self.ordered_pkts[1][scapy.all.TCP].ack
def __generate_handshake(self):
if self.stream.tcp_state.syn_seen is False:
return list()
syn = scapy.all.TCP(sport = self.stream.sport, dport = self.stream.dport,
flags = 'S', seq = self.seq, ack = 0)
self.seq += 1
synack = scapy.all.TCP(sport = self.stream.dport, dport = self.stream.sport,
flags = 'SA', seq = self.ack, ack = self.seq)
self.ack += 1
ack = scapy.all.TCP(sport = self.stream.sport, dport = self.stream.dport,
flags = 'A', seq = self.seq, ack = self.ack)
handshake = list()
handshake += self.ip2dst/syn
handshake += self.ip2src/synack
handshake += self.ip2dst/ack
handshake[0].time = self.ordered_pkts[0].time # time(TCP-SYN)
handshake[1].time = self.ordered_pkts[1].time # time(TCP-SYN-ACK)
handshake[2].time = self.ordered_pkts[2].time # time(TCP-ACK)
return handshake
def __generate_payload(self, split_data, bytes_per_packet):
packets = list()
for i in range(0, len(split_data.payload), bytes_per_packet):
payload = split_data.payload[i:i + bytes_per_packet]
if split_data.direction is False: # reverse direction e.g. server -> client?
iphdr_src = self.ip2src
iphdr_dst = self.ip2dst
tcphdr_sport = self.stream.sport
tcphdr_dport = self.stream.dport
tcphdr_seq = self.seq
tcphdr_ack = self.ack
else:
iphdr_src = self.ip2dst
iphdr_dst = self.ip2src
tcphdr_sport = self.stream.dport
tcphdr_dport = self.stream.sport
tcphdr_seq = self.ack
tcphdr_ack = self.seq
iphdr = iphdr_dst
tcphdr = scapy.all.TCP(sport = tcphdr_sport, dport = tcphdr_dport,
flags = 'PA', seq = tcphdr_seq, ack = tcphdr_ack)
p = iphdr/tcphdr/scapy.all.Raw(load = payload)
p.time = split_data.time
packets += p
tcphdr_seq += len(payload)
iphdr = iphdr_src
tcphdr = scapy.all.TCP(sport = tcphdr_dport, dport = tcphdr_sport,
flags = 'A', seq = tcphdr_ack, ack = tcphdr_seq)
p = iphdr/tcphdr
p.time = split_data.time
packets += p
if split_data.direction is False:
self.seq = tcphdr_seq
self.ack = tcphdr_ack
else:
self.seq = tcphdr_ack
self.ack = tcphdr_seq
return packets
def __generate_finish(self, split_data):
packets = list()
# We are always closing the connection from the client side for now.
iphdr = self.ip2dst
tcphdr = scapy.all.TCP(sport = self.stream.sport, dport = self.stream.dport,
flags = 'FA', seq = self.seq, ack = self.ack)
p = iphdr/tcphdr
p.time = split_data.time
packets += p
self.seq += 1
iphdr = self.ip2src
tcphdr = scapy.all.TCP(sport = self.stream.dport, dport = self.stream.sport,
flags = 'FA', seq = self.ack, ack = self.seq)
p = iphdr/tcphdr
p.time = split_data.time
packets += p
self.ack += 1
iphdr = self.ip2dst
tcphdr = scapy.all.TCP(sport = self.stream.sport, dport = self.stream.dport,
flags = 'A', seq = self.seq, ack = self.ack)
p = iphdr/tcphdr
p.time = split_data.time
packets += p
return packets
@staticmethod
def build_stream_key(pkt):
return str(pkt['IP'].src) + ':' + str(pkt['TCP'].sport) + \
' -> ' + \
str(pkt['IP'].dst) + ':' + str(pkt['TCP'].dport)
def split(self):
data = []
seq_nos = {}
for pkt in self.ordered_pkts:
tcpp = pkt[scapy.all.TCP]
seq = tcpp.seq
key = TCPSplitStream.build_stream_key(pkt)
if not key in seq_nos:
seq_nos[key] = []
if seq in seq_nos[key]:
# retransmit
continue
if scapy.all.Raw in tcpp:
data.append(TCPSplitData(pkt.time, False if pkt.sport == self.stream.sport else True,
tcpp[scapy.all.Raw].load))
seq_nos[key].append(seq)
tcp_stream = self.__generate_handshake()
data.sort(key = lambda tcp_split_data: tcp_split_data.time)
for payload_packet in data:
tcp_stream += self.__generate_payload(payload_packet, MAX_BYTES_PER_PACKET)
tcp_stream += self.__generate_finish(data[-1:][0])
return tcp_stream
def printStreams(tse):
print('TCP Streams found:')
for stream in tse.summary():
print('\t' + stream)
if __name__ == '__main__':
parser = argparse.ArgumentParser()
parser.add_argument('input', type=str, help='PCAP input file')
parser.add_argument('-o', '--output', type=str, help='PCAP output file',
default=None)
parser.add_argument('-s', '--summary', action="store_true",
help='Print found TCP Streams to stdout',
default=False)
parser.add_argument('-l', '--length', type=int,
help='Split TCP payload every n bytes',
default=MAX_BYTES_PER_PACKET)
args = parser.parse_args()
tse = TCPStreamExtractor.TCPStreamExtractor(args.input)
if args.summary is True:
printStreams(tse)
MAX_BYTES_PER_PACKET = args.length
all_streams = list()
for session in tse.fwd_flows:
stream = tse.streams[session]
tss = TCPSplitStream(stream)
all_streams += tss.split()
if args.output is not None:
scapy.all.wrpcap(args.output, all_streams)
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