Assignment 1

1 files changed, 42 insertions, 0 deletions

diff --git a/netsec-assignment1-S4498062/exercise3/sniffer.py b/netsec-assignment1-S4498062/exercise3/sniffer.py
new file mode 100755
index 0000000..55416a8
--- /dev/null
+++ b/netsec-assignment1-S4498062/exercise3/sniffer.py
@@ -0,0 +1,42 @@
+#!/usr/bin/env python3
+
+import socket
+import struct
+
+def parse_udp(packet):
+    header_length = 8
+    header = packet[:header_length]
+    data = packet[header_length:]
+    (source_port, dest_port, data_length, checksum) = struct.unpack(
+            "!HHHH", header)
+    return source_port, dest_port, data_length, data, checksum
+
+def parse_ip(packet):
+    header_length_in_bytes = (packet[0] & 0x0f) * 4
+    header = packet[:20]
+    data = packet[header_length_in_bytes:]
+    length, protocol, src, dst = struct.unpack(
+            "!xxHxxxxxBxx4s4s", header)
+    header = {'length': length,
+            'protocol': protocol,
+            'source': src,
+            'destination': dst}
+    return header_length_in_bytes, header, data
+
+def format_ip(addr):
+    return '.'.join('%d'%i for i in addr)
+
+def main():
+    s = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_UDP)
+    while True:
+        raw, address = s.recvfrom(2 ** 16 - 1)
+        ip_header_len, ip_header, ip_payload = parse_ip(raw)
+        src_port, dst_port, udp_len, udp_data, udp_crc = parse_udp(ip_payload)
+        print("{}:{} --> {}:{}\nData length: {}\nChecksum: {}\n{}\n".format(
+            format_ip(ip_header['source']), src_port,
+            format_ip(ip_header['destination']), dst_port,
+            udp_len, udp_crc, udp_data))
+
+if __name__ == "__main__":
+    main()
+