Demonstrate pseudo-random IV generation for AES-CBC using a counter as IV input

aes_cbc_iv_example.py

#!/usr/bin/env python

from Crypto.Cipher import AES
from Crypto.Cipher import DES3

def add_padding(message):
    pad_len = 16 - (len(message) % 16)
    message += (' ' * pad_len)
    return message

# AES test

key='\x63\x5b\x76\xd1\x71\x5c\xdf\x2a\x69\x99\xc9\x0f\x3b\x23\x13\x02'
pkt_ctr_iv='\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01'
dummy_iv='\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'

# Using a dummy IV to encrypt a counter IV to create a pseudo random IV from the first block of ciphertext
# Allows the use of a simple counter as IV input to CBC mode.
obj_enc = AES.new(key, AES.MODE_CBC, dummy_iv)
new_iv = obj_enc.encrypt(pkt_ctr_iv)

message = "This is a sample message."
message = add_padding(message)
enc = obj_enc.encrypt(message)

obj_dec = AES.new(key, AES.MODE_CBC, new_iv)
dec = obj_dec.decrypt(enc)

if(dec != message):
    print("Error decrypting message")