Scapy Tcp Checksum Recalculation Odd Behaviour

I'm trying to do a TCP ACK Spoofing. I sniff one ACK packet from a pcap file and send it in a loop incrementing its ACK number as well as another option field. Sniffing Part: (Pres

Solution 1:

After a extended testing, I saw that, del ack_pkt[TCP].checksum deletes the checksum. But while converting to hex string with str(ack_pkt), I guess, it recalculates the checksum. After trying:

ack_pkt = sniff(offline="mptcpdemo.pcap", filter="tcp", count=15)[14]
del ack_pkt[TCP].chksum
print ack_pkt[TCP].chksum
printstr(ack_pkt)

It 1st prints the checksum as None. But while printing the hex string, I'm able to see that the checksum field is non zero and contains the actual recalculated checksum.

In the non-optimized code, inside the loop, the packet is converted to hex-string and hence it's re-calculating the checksum each time. But in the optimized version, conversion is outside the loop and hence it carries one value only.