encryption.py

#!/usr/bin/python

__author__      = "Michael Rightmire"
__copyright__   = "Copyright 2013, UTR Enterprises"
__credits__     = ["Michael Rightmire"]
__license__     = "UTR Enterprises"
__version__     = "0.9.0"
__maintainer__  = "Michael Rightmire"
__email__       = "RightmireM@UTR.Net"
__status__      = "Beta"

import Crypto.Util.randpool as crandom
from Crypto.Cipher import AES
import hashlib

# salt size in bytes
SALT_SIZE = 16
# number of iterations in the key generation
NUMBER_OF_ITERATIONS = 20
# the size multiple required for AES
AES_MULTIPLE = 16

def generate_key(password, salt, iterations):
    assert iterations > 0
    key = password + salt
    for i in range(iterations):
        key = hashlib.sha256(key).digest()
    return key

def pad_text(text, multiple):
    extra_bytes = len(text) % multiple
    padding_size = multiple - extra_bytes
    padding = chr(padding_size) * padding_size
    padded_text = text + padding
    return padded_text

def unpad_text(padded_text):
    padding_size = ord(padded_text[-1])
    text = padded_text[:-padding_size]
    return text

def encrypt(plaintext, password):
    salt = crandom.RandomPool(SALT_SIZE)
    salt = salt.get_bytes(SALT_SIZE)
    key = generate_key(password, salt, NUMBER_OF_ITERATIONS)
    cipher = AES.new(key, AES.MODE_ECB)
    padded_plaintext = pad_text(plaintext, AES_MULTIPLE)
    ciphertext = cipher.encrypt(padded_plaintext)
    ciphertext_with_salt = salt + ciphertext
    return ciphertext_with_salt

def decrypt(ciphertext, password):
    salt = ciphertext[0:SALT_SIZE]
    ciphertext_sans_salt = ciphertext[SALT_SIZE:]
    key = generate_key(password, salt, NUMBER_OF_ITERATIONS)
    cipher = AES.new(key, AES.MODE_ECB)
    padded_plaintext = cipher.decrypt(ciphertext_sans_salt)
    plaintext = unpad_text(padded_plaintext)
    return plaintext