checksumming part finish

This commit is contained in:
Nico Schottelius 2019-07-01 09:36:14 +02:00
parent b757a3c2b0
commit 92e1407729
2 changed files with 112 additions and 11 deletions

View file

@ -1,7 +1,77 @@
#!/usr/bin/python3
#from __future__ import unicode_literals
import ipaddress
from scapy.all import *
import array
import struct
# stolen from scapy (little endian system)
def checksum_scapy(pkt):
if len(pkt) % 2 == 1:
pkt += b"\0"
s = sum(array.array("H", pkt))
s = (s >> 16) + (s & 0xffff)
s += s >> 16
s = ~s
return (((s>>8)&0xff)|s<<8) & 0xffff
# 1. convert to array of "bytes"
# 2. import into an array
# 3. sum everything up
def sum_for_udp(packet):
sums = ""
sums += struct.pack("H", packet[UDP].sport)
sums += struct.pack("H", packet[UDP].dport)
sums += struct.pack("H", packet[UDP].len)
return sums
def sum_for_v6(packet):
# hdr.ipv6.src_addr, /* 128 */
# hdr.ipv6.dst_addr, /* 128 */
# meta.length_without_ip_header, /* 32 */
# 24w0, /* 24 */
# hdr.ipv6.next_header, /* 8 */
# /* total: 324 */
# // UDP header
# hdr.udp.src_port, /* 16 */
# hdr.udp.dst_port, /* 16 */
# hdr.udp.payload_length /* 16 */
# /* all: 372 */
# order does not matter!
sums = ""
sums += ipaddress.IPv6Address(packet[IPv6].src.decode("utf-8")).packed
sums += ipaddress.IPv6Address(packet[IPv6].dst.decode("utf-8")).packed
sums += struct.pack("H", packet[IPv6].plen)
sums += struct.pack("B", packet[IPv6].nh)
print("{} - {} - {}".format(len(sums), sums, checksum_scapy(sums)))
return sums
def sum_for_v4(packet):
# Get diffs -- for UDP
# udp_v4 =
# hdr.ipv4.src_addr,
# hdr.ipv4.dst_addr,
# 8w0,
# hdr.ipv4.protocol,
# meta.length_without_ip_header,
sums = ""
sums += ipaddress.IPv4Address(packet[IP].src.decode("utf-8")).packed
sums += ipaddress.IPv4Address(packet[IP].dst.decode("utf-8")).packed
sums += struct.pack("H", packet[IP].len - 20) # -20 for ip header
sums += struct.pack("H", packet[IP].proto) # udp / tcp
return sums
if __name__ == '__main__':
p = []
@ -41,18 +111,16 @@ if __name__ == '__main__':
chk_new = packet_rebuild[UDP].chksum
print("chk1 = {} chk2={}".format(chk_old, chk_new))
# Get diffs -- for UDP
# udp_v4 =
# hdr.ipv4.src_addr,
# hdr.ipv4.dst_addr,
# 8w0,
# hdr.ipv4.protocol,
# meta.length_without_ip_header,
sums = ""
# // UDP header
# hdr.udp.src_port,
# hdr.udp.dst_port,
# hdr.udp.payload_length
if IP in packet:
sums += sum_for_v4(packet_rebuild)
if IPv6 in packet:
sums += sum_for_v6(packet_rebuild)
# if UDP in packet:
# sums += sum_for_udp(packet_rebuild)
print("Checksum-parts {} for {}".format(checksum_scapy(sums), packet_rebuild.__repr__()))
# Checksums:

View file

@ -384,6 +384,12 @@
| 2019-06-27 | | |
| | Target Hardware: code running | |
| | | |
| 2019-07-01 | | |
| | Meeting Laurent | |
| | | |
| | - Diff'ing in python | |
| | - Phasing in netpfga code | |
| | | |
| 2019-07-11 | | |
| | Integrated org-documentation into latex / export working | |
| | https://bastibe.de/2014-09-23-org-cite.html | |
@ -4893,6 +4899,33 @@ actual (tlast, tkeep, tdata) = (0, ffffffff, 000000000000000080fe403b0a0000000
*** 2019-06-24: find out how the expected/actual packet lines are generated
- afair: indirectly by running gen_testdata.py -> replace script
with port1
*** 2019-07-01: verify checksumming
#+BEGIN_CENTER
if struct.pack("H",1) == b"\x00\x01": # big endian
def checksum(pkt):
if len(pkt) % 2 == 1:
pkt += b"\0"
s = sum(array.array("H", pkt))
s = (s >> 16) + (s & 0xffff)
s += s >> 16
s = ~s
return s & 0xffff
else:
def checksum(pkt):
if len(pkt) % 2 == 1:
pkt += b"\0"
s = sum(array.array("H", pkt))
s = (s >> 16) + (s & 0xffff)
s += s >> 16
s = ~s
return (((s>>8)&0xff)|s<<8) & 0xffff
#+END_CENTER
*** 2019-07-01: 128 bit ipv6 struct -> no conversion!
- https://docs.python.org/2.7/library/struct.html
- .packed of ipaddress works
*** 2019-07-01: finish sum, use scapy checksum
*** 2019-07-01: meeting Laurent
** References / Follow up
*** RFC 791 IPv4 https://tools.ietf.org/html/rfc791
*** RFC 792 ICMP https://tools.ietf.org/html/rfc792