Python AES encryption without extra module

Question

Is it possible to encrypt/decrypt data with AES without installing extra modules? I need to send/receive data from C#, which is encrypted with the System.Security.Cryptography reference.

UPDATE I have tried to use PyAES, but that is too old. I updated some things to make that work, but it didn't. I've also can't install because it latest version is 3.3 while my version is 3.4.

Answer 1

I'm using Cryptography library.

Cryptography is an actively developed library that provides cryptographic recipes and primitives. It supports Python 2.6-2.7, Python 3.3+ and PyPy.

See this documentation for an example of how to use that library:

import os
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes

# Pseudo-random key and initialisation vector
key = os.urandom(32)           # (32*8=256-bit. AES also accepts 128/192-bit)
init_vector = os.urandom(16)   # (16*8=128-bit. AES only accepts this size)

# Setup module-specific classes
cipher = Cipher(algorithms.AES(key), modes.CBC(init_vector))
encryptor = cipher.encryptor()
decryptor = cipher.decryptor()

# Encrypt and decrypt data
cyphertext = encryptor.update(b"a secret message") + encryptor.finalize()
plaintext = decryptor.update(cyphertext) + decryptor.finalize()
print(plaintext) # 'a secret message'

Some notes explaining the example code:

• os.urandom is used for security instead of Python's random module. See this answer for more details.
• This article has more details about why an initialisation vector is used and what CBC (Cypher Block Chaining) mode is in AES encryption.
• The linked documentation explains classes specific to the cryptography module like algorithms or modes: "Cipher objects combine an algorithm such as AES with a mode like CBC or CTR."
• Old versions of the library (<3.1) required a backend object. This is deprecated since version 36.0 of the library.

Answer 2

PYAES should work with any version of Python3.x. No need to modify the library.

Here is a complete working example for pyaes CTR mode for Python3.x (https://github.com/ricmoo/pyaes)

import pyaes

# A 256 bit (32 byte) key
key = "This_key_for_demo_purposes_only!"
plaintext = "Text may be any length you wish, no padding is required"

# key must be bytes, so we convert it
key = key.encode('utf-8')

aes = pyaes.AESModeOfOperationCTR(key)    
ciphertext = aes.encrypt(plaintext)

# show the encrypted data
print (ciphertext)

# DECRYPTION
# CRT mode decryption requires a new instance be created
aes = pyaes.AESModeOfOperationCTR(key)

# decrypted data is always binary, need to decode to plaintext
decrypted = aes.decrypt(ciphertext).decode('utf-8')

# True
print (decrypted == plaintext)

Let me know if you get any errors

Answer 3

The available Cryptographic Services available in the Standard Library are those. As you can see AES is not listed, but is suggest to use pycrypto which is an extra module.

You just have to install it using pip, or easy_install and then as showed in pycrypto's page:

from Crypto.Cipher import AES
obj = AES.new('This is a key123', AES.MODE_CBC, 'This is an IV456')
message = "The answer is no"
print obj.encrypt(message)

The only other way without using an extra module would be to code the function yourself, but what's the difference of downloading an extra module and use that instead?

If you want a pure Python implementation of AES that you can download and import check pyaes.

Answer 4

Here is a self-contained implementation of AES compatible with Python 3.

Example usage:

aesmodal = AESModeOfOperation() 
key = [143,194,34,208,145,203,230,143,177,246,97,206,145,92,255,84]
iv = [103,35,148,239,76,213,47,118,255,222,123,176,106,134,98,92]

size = aesmodal.aes.keySize["SIZE_128"]

mode,orig_len,ciphertext = aesmodal.encrypt("Hello, world!", aesmodal.modeOfOperation["OFB"], key, size, iv)
print(ciphertext)
plaintext = aesmodal.decrypt(ciphertext, orig_len, mode, key, size, iv)
print(plaintext)

Answer 5

To add to @enrico.bacis' answer: AES is not implemented in the standard library. It is implemented in the PyCrypto library, which is stable and well tested. If you need AES, add PyCrypto as a dependency of your code.

While the AES primitives are, in theory, simple enough that you could write an implementation of them in pure Python, it is strongly recommended that you not do so. This is the first rule of crypto: don't implement it yourself. In particular, if you're just rolling your own crypto library, you'll almost certainly leave yourself open to some kind of side-channel attack.

Answer 6

Python 3.6 with cryptography module

from cryptography.fernet import Fernet
key = Fernet.generate_key()
f = Fernet(key)
token = f.encrypt(b"my deep dark secret")
print(token)


f.decrypt(token)