"TypeError: Object type <class 'str'> cannot be passed to C code when encrypting an image

Question

I am trying to encrypt an image file, but when I try to execute my code, I get the error:

TypeError: Object type <class 'str'> cannot be passed to C code

I will really appreciate any help on how to fix this error, I'm a beginner in using python.

Here is my code:

from PIL import Image
#from PIL.Image import core as image
import os
import sys
from Crypto.Cipher import AES

Block_size=16 
IV_size=16 
def encrypt_file(input_file,output_file,cipher_mode):
          input_img=Image.open('/content/Linux-icon.png')
          key="770A8A65DA156D24EE2A093277530142"
          if cipher_mode=='CBC':
               mode=AES.MODE_CBC
          #elif cipher_mode=='CBC':
              # mode=AES.MODE_CBC
          else:
              mode=AES.MODE_CFB
          i=os.urandom(IV_size)
          aes=AES.new(key,mode,i)
          img_str=input_img.tostring()
          #Pad the image string to the input block size
          img_pad_lenght=Block_size-len(img_str)/Block_size

          img_str+=img_pad_lenght*"~"
          #generate the encrypted image string
          encrypted_img_str=aes.encrypt(encode(img_str))

          #create an image from the encrypted string
          encrypted_img=Image.frombuffer('RGB',input_img.size, encrypted_img_str,'raw','RGB',0,1)
          #create and save the output image
          encrypted_img.save('/content/Linux-icon1.png','PNG')
          print("Encrypted using AES in " + cipher_mode + " mode and saved to \"" + output_filename + "\"!")

Thanks in advance

Answer 1

Your code have some issues read the code comments. As a side note: try to encrypt BMP images in ECB mode to see why it's bad to use encryption in ECB mode.

# deleted non needed imports
from PIL import Image
import os
from Crypto.Cipher import AES

Block_size = 16
IV_size = 16
def encrypt_file(input_file,output_file,cipher_mode):
            # use function input file name not a fixed one
          input_img = Image.open(input_file)

          # must be in bytes
          key = b"770A8A65DA156D24EE2A093277530142"
          if cipher_mode=='CBC':
               mode = AES.MODE_CBC
          else:
              mode = AES.MODE_CFB

          iv = os.urandom(IV_size)
          aes = AES.new(key, mode, iv)
          img_str = input_img.tobytes()

            # To get padding needed use mod operator
          img_pad_lenght = Block_size - (len(img_str) % Block_size)

            # Add padding of null bytes
          img_str += img_pad_lenght * b"\0"
          print(len(img_str))
            # There is no built in encode function in python encode is a string method
            # must be applied to a string
          encrypted_img_str = aes.encrypt(img_str)

          encrypted_img = Image.frombuffer('RGB', input_img.size, encrypted_img_str, 'raw', 'RGB', 0, 1)
          encrypted_img.save(output_file, 'PNG')

            # there is no variable as outputfilename only output_file
          print("Encrypted using AES in " + cipher_mode + " mode and saved to \"" + output_file + "\"!")