AES.py

import os
from Crypto.Cipher import AES
from Crypto.Hash import SHA256
from Crypto import Random

def encrypt(key, filename):
    chunkSize = 64*1024
    outputFile = 'e-'+filename
    filesize = str(os.path.getsize(filename)).zfill(16)
    IV = Random.new().read(16)

    encryptor = AES.new(key, AES.MODE_CBC, IV)

    with open(filename, 'rb') as infile:
        with open(outputFile, 'wb') as outfile:
            outfile.write(filesize.encode('utf-8'))
            outfile.write(IV)

            while True:
                chunk = infile.read(chunkSize)
                if chunk == 0:
                    break
                elif len(chunk) % 16 != 0:
                    chunk += b' ' * (16 - len(chunk) % 16)
                outfile.write(encryptor.encrypt(chunk))


def decrypt(key, filename):
    chunksize = 64*1024
    outputfile = filename[11:]

    with open(filename, 'rb') as infile:

        filesize = int(infile.read(16))
        IV = infile.read(16)
        decryptor = AES.new(key, AES.MODE_CBC, IV)

        with open(outputfile, 'wb') as outfile:
            while True:
                chunk = infile.read(chunksize)

                if len(chunk) == 0:
                    break
                outfile.write(decryptor.decrypt(chunk))
            outfile.truncate(filesize)

def getKey(password):
    hasher = SHA256.new(password.encode('utf-8'))
    return hasher.digest()

def Main():
    choice = input('(E)ncrypt, or (D)ecrypt?: ')

    if choice == 'e':
        filename = input('File to encrypt: ')
        password = input('Password: ')
        encrypt(getKey(password), filename)
        print('Done')

    if choice == 'd':
        filename = input('File to decrypt: ')
        password = input('Password: ')
        decrypt(getKey(password), filename)
        print('Done decrypting.')
    else:
        print('Invalid input')
        Main()

if __name__ == '__main__':
    Main()