#!/usr/bin/python

import socket
import struct
import threading
import time
import sys
import random
import re
import logging
from optparse import OptionParser
from scapy.all import *

def calculate_tcp_length(pkt):
        iphdr_len = pkt[IP].ihl * 4
        total_len = pkt[IP].len
        tcp_hdrlen = pkt[TCP].dataofs * 4
        tcp_payload_len = total_len - iphdr_len - tcp_hdrlen
        return tcp_payload_len

def recalculate_tcp_md5_signature(pkt,password):
    
    destination_ip = pkt[IP].dst
    source_ip = pkt[IP].src
    reserved = 0
    protocol = socket.IPPROTO_TCP

    tcp_hdrlen = pkt[TCP].dataofs *4
    tcp_payload_len =calculate_tcp_length(pkt)
    total_length = tcp_hdrlen + tcp_payload_len
    
    #pseudo header
    psh = struct.pack("!4s4sBBH",
                      source_ip,
                      destination_ip,
                      reserved,
                      protocol,
                      total_length
                      )

    iphdr_len = pkt[IP].ihl * 4
    tcp_header = pkt[iphdr_len:iphdr_len+20]
    tcp_payload = pkt[iphdr_len+20:]
    
    tcp_sport = pkt[TCP].sport
    tcp_dport = pkt[TCP].dport
    tcp_seq = pkt[TCP].seq
    tcp_ack = pkt[TCP].ack
    tcp_dataofs = pkt[TCP].dataofs
    tcp_reserved = pkt[TCP].reserved
    tcp_flags = pkt[TCP].flags
    tcp_window = pkt[TCP].window
    tcp_chksum = pkt[TCP].chksum
    tcp_urgptr = pkt[TCP].urgptr


    
    reassemble_pkt[TCP].seq = seq
	reassemble_pkt[TCP].ack = ack
	reassemble_pkt[TCP].sport = sport
	reassemble_pkt[TCP].dport = dport

	if tsecr!=None and tsval!=None:
		if reassemble_pkt[TCP].options != None:
			#logging.info("tcp options:",reassemble_pkt[TCP].options)
			listopt = []
			for opt in reassemble_pkt[TCP].options:
				if opt[0] != 'Timestamp':
					listopt.append(opt)
				else:
                                        
					timestamp = ('Timestamp',(tsval,tsecr))
					
					listopt.append(timestamp)

		reassemble_pkt[TCP].options = listopt		
		#logging.info("11111tcp options:",reassemble_pkt[TCP].options)

	del reassemble_pkt[TCP].chksum
	del reassemble_pkt[IP].chksum