decoder the payload that got from pcap files

ctp_quiz8_decoder.py

#!/usr/bin/python2.7
import string
import random
from base64 import b64encode, b64decode

FLAG = 'flag{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx}'

enc_ciphers = ['rot13', 'b64e', 'caesar']
dec_ciphers = ['rot13', 'b64d', 'caesard']

def rot13(s):
 _rot13 = string.maketrans( 
     "ABCDEFGHIJKLMabcdefghijklmNOPQRSTUVWXYZnopqrstuvwxyz", 
     "NOPQRSTUVWXYZnopqrstuvwxyzABCDEFGHIJKLMabcdefghijklm")
 return string.translate(s, _rot13)

def b64e(s):
 return b64encode(s)

def b64d(s):
 return b64decode(s)

def caesar(plaintext, shift=3):
    alphabet = string.ascii_lowercase
    shifted_alphabet = alphabet[shift:] + alphabet[:shift]
    table = string.maketrans(alphabet, shifted_alphabet)
    return plaintext.translate(table)

def caesard(cipher, shift=-3):
    alphabet = string.ascii_lowercase
    shifted_alphabet = alphabet[shift:] + alphabet[:shift]
    table = string.maketrans(alphabet, shifted_alphabet)
    return cipher.translate(table)

def encode(pt, cnt=50):
 tmp = '2{}'.format(b64encode(pt))
 for cnt in xrange(cnt):
  c = random.choice(enc_ciphers)
  i = enc_ciphers.index(c) + 1
  _tmp = globals()[c](tmp)
  tmp = '{}{}'.format(i, _tmp)

 return tmp

def decode(cipher):
   while 'flag' not in cipher:

      i = int(cipher[0])
      raw = cipher[1:]
      print '# ['+ str(i) + '] <= '+cipher[0]
      print 'raw: '+ cipher[0:] +', Running function :' + dec_ciphers[i-1]
      decoded_text = globals()[dec_ciphers[i-1]](raw)
      print 'decoded: '+decoded_text+'\n'
      cipher = decoded_text
   print cipher

if __name__ == '__main__':
 #print encode(FLAG, cnt=?)
 with open('payload.txt', 'r') as raw:
   print decode(raw.read().strip())