Implementing AES/ECB/PKCS5 padding in Python

Question

I am trying to implement a python program to encrypt a plain text using AES/ECB/PKCS5 padding. The output I am getting is slightly different from expected.

Python3 program:

import base64
from Crypto.Cipher import AES

 
def add_to_16(value):
    while len(value) % 16 != 0:
        value += '\0'
    return str.encode (value) # returns bytes
 

# Encryption method
def encrypt(text):
         # Secret key 
    key='92oifgGh893*cj%7' 

         # Text to be encrypted
         # Initialize encryptor
    aes = AES.new(key, AES.MODE_ECB) 

         # Aes encryption to be
    encrypt_aes = aes.encrypt(add_to_16(text)) 

         # Converted into a string with base64
    encrypted_text = str(base64.encodebytes (encrypt_aes), encoding = 'utf-8')

    print(encrypted_text)
    return encrypted_text

if __name__ == '__main__': 

    text = '{  "Message": "hello this is a plain text" , "user":"john.doe", "Email":"[email protected]}'
    entrypted_text = encrypt(text)

The output for above program is:

oo8jwHQNQnBwVUsJ5piShFRM3PFFIfULwcoFOEQhPMTAvexSr6eE9aFLVQTpAKBFkGi8vNbtScvyexSxHBlwVapJ5Szz1JPR9q9cHHJYYMzGocln4TRPFQ6S3e8jjVud

where as when verified with 3rd party tools online, the results is:

oo8jwHQNQnBwVUsJ5piShFRM3PFFIfULwcoFOEQhPMTAvexSr6eE9aFLVQTpAKBFkGi8vNbtScvyexSxHBlwVapJ5Szz1JPR9q9cHHJYYMwnIIuNCUVn/IExpxebqXV1

Can someone please guide me where I am doing wrong?

Answer 1

I have framed the code with below for padding with PKCS5 and is working as expected.

block_size=16
pad = lambda s: s + (block_size - len(s) % block_size) * chr(block_size - len(s) % block_size)

and the encrypt method was re-written as below:

def encrypt(plainText,key):
    
    aes = AES.new(key, AES.MODE_ECB)    
    encrypt_aes = aes.encrypt(pad(plainText))   
    encrypted_text = str(base64.encodebytes (encrypt_aes), encoding = 'utf-8')
    return encrypted_text