Encryption using pycrypto, AES, and PKCS5 padding

py3_AES.py

'''
Author: komuw/pycrypto_AES.py

Security issues:
+ https://stackoverflow.com/questions/2641720/for-aes-cbc-encryption-whats-the-importance-of-the-iv
+ https://defuse.ca/cbcmodeiv.htm
+ https://passingcuriosity.com/2009/aes-encryption-in-python-with-m2crypto/
'''

from Crypto.Cipher import AES
from Crypto import Random
import base64

block_size = AES.block_size


#unpad = lambda s : s[0:-ord(s[-1])]

def pad(plain_text):
    """
    func to pad cleartext to be multiples of 8-byte blocks.
    If you want to encrypt a text message that is not multiples of 8-byte blocks, 
    the text message must be padded with additional bytes to make the text message to be multiples of 8-byte blocks.
    """
    number_of_bytes_to_pad = block_size - len(plain_text) % block_size
    ascii_string = chr(number_of_bytes_to_pad)
    padding_str = number_of_bytes_to_pad * ascii_string
    padded_plain_text =  plain_text + padding_str
    return padded_plain_text


key='b'* 32
plain="Hence, it wants a string of 8-bit bytes. You create those in Python 3 with the b'' syntax."
plain = pad(plain)

#iv = b'0000000000000000'
iv = b'\0'* 16

cipher = AES.new(key.encode("utf-8"), AES.MODE_CBC, iv )
encrypted_text = cipher.encrypt( plain.encode("utf-8") )

print (base64.b64encode(encrypted_text).decode("utf-8"))