A script I used to learn padding oracle attacks

padding_oracle

#!/usr/bin/python
from base64 import b64encode,b64decode
import readline
import struct
from Crypto.Cipher import AES
from sys import argv,exit
from os import urandom
from random import random
BS = 16
pad = lambda s: s + (BS - len(s) % BS) * chr((BS - len(s) % BS))
def encrypt(iv,key,plain):
	return AES.new(key,AES.MODE_CBC,iv).encrypt(plain)
def decrypt(iv,key,cipher):
	plaintext = AES.new(key,AES.MODE_CBC,iv).decrypt(cipher)
	try:
		string = "%s" % (ord(plaintext[len(plaintext)-1]))
		#print "padding length      : '%s'" % (string) <--- uncomment this if you're havin a hard time with the attack :) 
		#print "intermediated value : '%s'" % (pretty_print(plaintext))
	except ValueError,e:
		print "decrypt:",e
		raise e
	padding_length = int(string)
	incorrect = False
	for c in plaintext[len(plaintext)-padding_length:]:
		try:
			c = int("%s" % (ord(c)))
		except:
			print "c convert:",e
			raise e
		if c != padding_length:
			incorrect = True
	if incorrect == True:
		return False  
	return plaintext[:len(plaintext)-padding_length]
	 
def gen_rand_plaintext(length):
	return b64encode("".join([chr(int(random()*1000)%255) for c in range(length)]))
def pretty_print(text):
	string = " ".join([ "%02x" % (ord(c)) for c in text])
	return string
def unpretty_print(text):
	return ''.join([chr(int(c,16)) for c in text.split(" ")])
def rlinput(prompt,prefill=''):
	readline.set_startup_hook(lambda: readline.insert_text(prefill))	
	try:
		return raw_input(prompt)
	finally:
		readline.set_startup_hook()
def block_wise_print(text):
	
	string = " "
	newlines = 0
	char_count = 0
	chars = text.split(" ")
	for char in chars:
		string += char+" "
		char_count+=1
		if char_count % 16 == 0:
			string += "\n"
	return string[1:]
if __name__ == "__main__":
	while True:
		plaintext = pad("P"*33)
		key = "A"*32
		iv = "B"*16
		cipher = encrypt(iv,key,plaintext)
		plaintext = decrypt(iv,key,cipher)
		print "plaintext [%s]:" % (len(plaintext))
		print block_wise_print(pretty_print(plaintext))
		print "cipher    [%s]:" % (len(cipher))
		print block_wise_print(pretty_print(cipher))
		print "decrypted [%s]:" % (len(plaintext))
		print block_wise_print(pretty_print(plaintext))
		while True:
			line = rlinput('>',pretty_print(cipher))
			cipher = unpretty_print(line)	
			line = line.split(" ")	
			user_cipher = ''.join([chr(int(c,16)) for c in line])
			plain = decrypt(iv,key,user_cipher)
			if plain != False:
				print "decrypted [%s]:" % (len(plain))
				print block_wise_print(pretty_print(plain))
			print "[x]",plain