AES encryption differences in Ruby vs Python

Question

I'm trying to encrypt a message using AES-256-CBC but I get different behavior in Ruby and Python versions. It seems like Python's AES encryption does not add a suffix.

require 'base64'
require 'aescrypt'

key = "z\r}\xE6\xB5\xB0P:\x80D@+\x96S\xAB (\x87\xDD#3x\xB9\xF3\xB4\xE7*qTKz\xC1"
iv = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
data = "\xC7u\xE7\xB7W\xED\xE60\xCD\n\xA1\x11;\xD1\x02f\x1A\xB3\x88)\xCAR\xA6B*\xB7\x82\x86/&\x86F"

Base64.encode64(AESCrypt.encrypt_data(data, key, iv, "AES-256-CBC"))

=> "ldB7M0nr+FP6I9NiogtvysUFfUC2vIt6Hj7cwzEiUEal76Cpyc+x6RTiHgkq\n6j7n\n"

Whereas in Python using cryptography:

from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from cryptography.hazmat.backends import default_backend
import base64
backend = default_backend()

key = "z\r}\xE6\xB5\xB0P:\x80D@+\x96S\xAB (\x87\xDD#3x\xB9\xF3\xB4\xE7*qTKz\xC1"
iv = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
data = "\xC7u\xE7\xB7W\xED\xE60\xCD\n\xA1\x11;\xD1\x02f\x1A\xB3\x88)\xCAR\xA6B*\xB7\x82\x86/&\x86F"

cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=backend)
encryptor = cipher.encryptor()
ct = encryptor.update(data) + encryptor.finalize()
base64.b64encode(ct)

=> 'ldB7M0nr+FP6I9NiogtvysUFfUC2vIt6Hj7cwzEiUEY='

You can see the encrypted text produced by Ruby library has extra 16 bytes. I have Java code as well which produces exact same ciphertext as Ruby version. Python code is behaving oddly. How can I change the Python code so that it produces the same ciphertext?

I just remembered I wrote an answer for AES CBC using the cryptography package a few months ago. You may find it helpful. Note the PKCS7 padding. stackoverflow.com/a/50063211/4014959 — PM 2Ring
– PM 2Ring, Commented Sep 15, 2018 at 13:24

President James K. Polk · Accepted Answer · 2018-09-15 13:22:42Z

2

A friend pointed out the problem: the encrypt method requires padded data:

from Crypto.Util.Padding import pad
ct = encryptor.update(pad(data,16)) + encryptor.finalize()

edited Sep 15, 2018 at 13:22

President James K. Polk

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answered Sep 15, 2018 at 10:50

curiousboy

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1 Comment

Maarten Bodewes Over a year ago

You should be able to accept your own answer by now.

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