byte problems while encrypting with AES

Question

i wrote a code using Crypto.cipher that will go over all the files in the directory/sub-directory and encrypt them using AES-ECB. now the problem is that for some reason i get this error:

raise ValueError("Error %d while encrypting in ECB mode" % result) ValueError: Error 3 while encrypting in ECB mode

i tried converting the bytes to base64 and i still got the same problem, i thought at first that it might just be certain files that are encoded in a different way but then i took a look at the list and some of the files that gave this exception are .txt and just have some numbers in them so im not sure what the problem is.

with open(loc, 'rb') as file:
     data = file.read()
     Edata = Encrypt(data)

This is how i encrypt it:

def Encrypt(msg): #AES
    pad = lambda x: x + (SIZE - len(x) % SIZE) * PADDING
    print(type(msg))
    msg = pad(msg)
    cipher = AES.new(hkey,AES.MODE_ECB)
    cipherTxt = cipher.encrypt(msg)
    return cipherTxt

edit: python 3.6

def Decrypt(msg): #AES
    decipher = AES.new(hkey,AES.MODE_ECB)
    plain = decipher.decrypt(msg)
    index = plain.find(b".")
    original = msg[:index]
    return original

Answer 1

Encrypting binary data works with my crypto package (from anaconda). You may be using a different package - mine will error if you try to encrypt a string. This may just be a straw man, but this works for me:

from Crypto.Cipher import AES
from Crypto.Hash import SHA256
import random

password = "temp"
hashObj = SHA256.new(password.encode("utf-8"))
hkey = hashObj.digest()

def Encrypt(msg, blocksize=16):
    """encrypt msg with padding to blocksize. Padding rule is to fill with
    NUL up to the final character which is the padding size as an 8-bit
    integer (retrieved as `msg[-1]`)
    """
    assert blocksize > 2 and blocksize < 256
    last = len(msg) % blocksize
    pad = blocksize - last
    random_pad = bytes(random.sample(range(255), pad-1))
    msg = msg + random_pad + bytes([pad])
    cipher = AES.new(hkey,AES.MODE_ECB)
    cipherTxt = cipher.encrypt(msg)
    return cipherTxt

def Decrypt(msg): #AES
    decipher = AES.new(hkey,AES.MODE_ECB)
    print('msg size', len(msg))
    plain = decipher.decrypt(msg)
    print('plain', plain)
    original = plain[:-plain[-1]]
    return original


# test binary data
sample = bytes(range(41))
print('sample', sample)
encrypted = Encrypt(sample, 16)
print('encrypted', encrypted)
print(len(sample), len(encrypted))
decrypted = Decrypt(encrypted)
print('decrypted', decrypted)
print('matched', decrypted == sample)

# test blocksize boundary
sample = bytes(range(48))
decrypted = Decrypt(Encrypt(sample))
print('on blocksize', sample==decrypted)