fileencrypt.py

# ---------------------------------------
#
# Sample application to encrypt and decrypt 
# files using AES
#
# requires pycrypto
#
# ---------------------------------------


import os, random, struct
from Crypto.Cipher import AES
from Crypto import Random
import boto3
import base64
import hashlib


BLOCK_SIZE = 16
CHUNK_SIZE = 64 * 1024

def encrypt_file(password, in_filename, out_filename):

    key = hashlib.sha256(password.encode("utf-8")).digest()

    iv = Random.new().read(AES.block_size)
    encryptor = AES.new(key, AES.MODE_CBC, iv)
    filesize = os.path.getsize(in_filename)

    with open(in_filename, 'rb') as infile:
        with open(out_filename, 'wb') as outfile:
            outfile.write(struct.pack('<Q', filesize))
            outfile.write(iv)

            while True:
                chunk = infile.read(CHUNK_SIZE)
                if len(chunk) == 0:
                    break
                elif len(chunk) % 16 != 0:
                    chunk += ' '.encode("utf-8") * (16 - len(chunk) % 16)

                outfile.write(encryptor.encrypt(chunk))


def decrypt_file(password, in_filename, out_filename):

    key = hashlib.sha256(password.encode("utf-8")).digest()

    with open(in_filename, 'rb') as infile:
        origsize = struct.unpack('<Q', infile.read(struct.calcsize('Q')))[0]
        iv = infile.read(16)
        decryptor = AES.new(key, AES.MODE_CBC, iv)

        with open(out_filename, 'wb') as outfile:
            while True:
                chunk = infile.read(CHUNK_SIZE)
                if len(chunk) == 0:
                    break
                outfile.write(decryptor.decrypt(chunk))

            outfile.truncate(origsize)


# ------------------------
#
# Main program
#
# ------------------------

password = 'kitty and the kat'

encrypt_file(password,"afile1_dec.txt", out_filename="afile1_dec.txt.enc")
decrypt_file(password, "afile1_dec.txt.enc", out_filename="afilenew_dec.txt")