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#!/usr/bin/env python
# Thu, 13 Mar 14 (PDT)
# arp-anon.py: Anonymise IPv4 addresses in ARP records
# Copyright (C) 2015, Nevil Brownlee, U Auckland | WAND
# python arp-anon.py pcapfile:anon-v4.pcap pcapfile:first-n.pcap 30
from plt_testing import *
#import sys # argv, exit
in_fn = 'anon-v4.pcap'
#doc_ipv4 = IPprefix.from_s('192.168.0.0/24') # IPv4 'documentation' prefix
test_ipv4 = ipp.from_s('17.34.51.68') # test prefix
new_addr = test_ipv4.addr # 4-byte bytearray
print "test_ipv4 = %s" % test_ipv4
print "new_addr = %02x %02x %02x %02x" % (
new_addr[0], new_addr[1], new_addr[2], new_addr[3])
t = get_example_trace(in_fn)
ot = plt.output_trace('pcapfile:arp-changed.pcap')
ot.start_output()
print "files opened ..."
n = nip = 0; nudp = 0
for pkt in t:
n += 1
l3 = pkt.layer3
if l3.ethertype == 0x0806: # ARP
d = l3.data # Decode the ARP packet
hw_type = d[0]*256 + d[1]
protocol_type = d[2]*256 + d[3]
hln = d[4] # Length of h/w address
pln = d[5] # Length of protocol address
opcode = d[6]*256 + d[7]
print "hrd=%d, pro=%04x, hln=%d, pln=%d, opcode=%04x" % (
hw_type, protocol_type, hln, pln, opcode)
sax = 8+hln; tax = sax+pln+hln # Change sender and
print "sax=%d, tax=%d" % (sax, tax)
# CAUTION: python will replace a slice by a longer on,
# thus adding elements into a (byte)array.
# Here we're careful to replace 4 byte with another 4!
d[sax:sax+pln] = new_addr # target addresses in d
d[tax:tax+pln] = new_addr
l3.data = d # Write changed addresses into pkt
# pkt.layer3.data = d # This also works
ot.write_packet(pkt)
if n == 5:
break
ot.close_output; t.close
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