| *********************** |
| Calling Scapy functions |
| *********************** |
| |
| This section provides some examples that show how to benefit from Scapy |
| functions in your own code. |
| |
| UDP checksum |
| ============ |
| |
| The following example explains howto use the checksum() function to compute and |
| UDP checksum manually. The following steps must be performed: |
| |
| 1. compute the UDP pseudo header as described in RFC768 |
| 2. build an UDP packet with Scapy with p[UDP].chksum=0 |
| 3. call checksum() with the pseudo header and the UDP packet |
| |
| :: |
| |
| from scapy.all import * |
| |
| # Get the UDP checksum computed by Scapy |
| packet = IP(dst="10.11.12.13", src="10.11.12.14")/UDP()/DNS() |
| packet = IP(raw(packet)) # Build packet (automatically done when sending) |
| checksum_scapy = packet[UDP].chksum |
| |
| # Set the UDP checksum to 0 and compute the checksum 'manually' |
| packet = IP(dst="10.11.12.13", src="10.11.12.14")/UDP(chksum=0)/DNS() |
| packet_raw = raw(packet) |
| udp_raw = packet_raw[20:] |
| # in4_chksum is used to automatically build a pseudo-header |
| chksum = in4_chksum(socket.IPPROTO_UDP, packet[IP], udp_raw) # For more infos, call "help(in4_chksum)" |
| |
| assert(checksum_scapy == chksum) |
