Little abstraction for PyCrypto

crypto_utils.py

import base64

from Crypto import Random
from Crypto.Cipher import AES


BLOCK_SIZE = 16

pad = lambda s: s + (BLOCK_SIZE - len(s) % BLOCK_SIZE) * chr(BLOCK_SIZE - len(s) % BLOCK_SIZE)
unpad = lambda s: s[0:-ord(s[-1])]


class AESCipher(object):
    def __init__(self, key):
        self.key = key

    def encrypt(self, raw):
        raw = pad(raw)
        iv = Random.new().read(AES.block_size)
        cipher = AES.new(self.key, AES.MODE_CBC, iv)
        return base64.b64encode(iv + cipher.encrypt(raw))

    def decrypt(self, enc):
        enc = base64.b64decode(enc)
        iv = enc[:BLOCK_SIZE]
        cipher = AES.new(self.key, AES.MODE_CBC, iv)
        return unpad(cipher.decrypt(enc[BLOCK_SIZE:]))


cipher = AESCipher(key="x" * 32)
text = "Hello, world!"
print(text)
encrypted = cipher.encrypt(text)
print(encrypted)
decrypted = cipher.decrypt(encrypted)
print(decrypted)
assert text == decrypted

Sources:

• http://www.codekoala.com/blog/2009/aes-encryption-python-using-pycrypto/
• http://stackoverflow.com/a/12525165/458610