1

I am trying to run an image encryption and decryption program in Python 2.7. And I get following error enter image description here https://i.stack.imgur.com/pymJG.png

The encryption part works fine but the error is shown in the decryption part. I searched over internet but could not find a particular solution. I am new to programming. So, if someone could say what to do it will help me very much.

Here is the Code too

from Tkinter import *

from tkFileDialog import *

import tkMessageBox

import os

import Image 

import PIL

import math

from Crypto.Cipher import AES

import hashlib

import binascii

global password # make pass global var ```


# encryption method
# -----------------

def encrypt(imagename,password):

    # initialize variables

    plaintext = list()

    plaintextstr = ""

    
    # load the image
    im = Image.open(imagename)  # open target image
    pix = im.load()
    
    #print im.size   # print size of image (width,height)
    width = im.size[0]
    height = im.size[1]
    
    # break up the image into a list, each with pixel values and then append to a string
    for y in range(0,height):
        #print("Row: %d") %y  # print row number
        for x in range(0,width):
            #print pix[x,y]  # print each pixel RGB tuple
            plaintext.append(pix[x,y])
            
    # add 100 to each tuple value to make sure each are 3 digits long.  being able to do this is really just a PoC 
    # that you'll be able to use a raw application of RSA to encrypt, rather than PyCrypto if you wanted.
    for i in range(0,len(plaintext)):
        for j in range(0,3):
            plaintextstr = plaintextstr + "%d" %(int(plaintext[i][j])+100)
    
    # length save for encrypted image reconstruction
    relength = len(plaintext)
    
    # append dimensions of image for reconstruction after decryption
    plaintextstr += "h" + str(height) + "h" + "w" + str(width) + "w"
    
    # make sure that plantextstr length is a multiple of 16 for AES.  if not, append "n".  not safe in theory
    # and i should probably replace this with an initialization vector IV = 16 * '\x00' at some point.  In practice
    # this IV buffer should be random.
    while (len(plaintextstr) % 16 != 0):
        plaintextstr = plaintextstr + "n"
    
    # encrypt plaintext
    obj = AES.new(password, AES.MODE_CBC, 'This is an IV456')
    ciphertext = obj.encrypt(plaintextstr)
    
    # write ciphertext to file for analysis
    cipher_name = imagename + ".crypt"
    g = open(cipher_name, 'w')
    g.write(ciphertext)
    
    # -----------------
    # construct encrypted image (not currently using since Tkinter isn't very nice)
    # -----------------
    def construct_enc_image():
        # hexlify the ciphertext    
        asciicipher = binascii.hexlify(ciphertext)

        # replace function
        def replace_all(text, dic):
            for i, j in dic.iteritems():
                text = text.replace(i, j)
            return text

        # use replace function to replace ascii cipher characters with numbers
        reps = {'a':'1', 'b':'2', 'c':'3', 'd':'4', 'e':'5', 'f':'6', 'g':'7', 'h':'8', 'i':'9', 'j':'10', 'k':'11', 'l':'12', 'm':'13', 'n':'14', 'o':'15', 'p':'16', 'q':'17', 'r':'18', 's':'19', 't':'20', 'u':'21', 'v':'22', 'w':'23', 'x':'24', 'y':'25', 'z':'26'}
        asciiciphertxt = replace_all(asciicipher, reps)

        # construct encrypted image
        step = 3
        encimageone=[asciiciphertxt[i:i+step] for i in range(0, len(asciiciphertxt), step)]
        # if the last pixel RGB value is less than 3-digits, add a digit a 1
        if int(encimageone[len(encimageone)-1]) < 100:
            encimageone[len(encimageone)-1] += "1"
        # check to see if we can divide the string into partitions of 3 digits.  if not, fill in with some garbage RGB values
        if len(encimageone) % 3 != 0:
            while (len(encimageone) % 3 != 0):
                encimageone.append("101")

        encimagetwo=[(int(encimageone[int(i)]),int(encimageone[int(i+1)]),int(encimageone[int(i+2)])) for i in range(0, len(encimageone), step)]    

        # make sizes of images equal
        while (int(relength) != len(encimagetwo)):
            encimagetwo.pop()

        # encrypted image
        encim = Image.new("RGB", (int(width),int(height)))
        encim.putdata(encimagetwo)
   
        #encim.show()
        # alert success and path to image
        enc_success(cipher_name)
        
    construct_enc_image()
    
# decryption method

# -----------------
def decrypt(ciphername,password):
    
    # reach ciphertext into memory
    cipher = open(ciphername,'r')
    ciphertext = cipher.read() 

    
    # decrypt ciphertext with password
    obj2 = AES.new(password, AES.MODE_CBC, 'This is an IV456')
    decrypted = obj2.decrypt(ciphertext)
    
    # parse the decrypted text back into integer string
    decrypted = decrypted.replace("n","")
    
    # extract dimensions of images
    newwidth = decrypted.split("w")[1]
    newheight = decrypted.split("h")[1]
    
    # replace height and width with emptyspace in decrypted plaintext
    heightr = "h" + str(newheight) + "h"
    widthr = "w" + str(newwidth) + "w"
    decrypted = decrypted.replace(heightr,"")
    decrypted = decrypted.replace(widthr,"")

    # reconstruct the list of RGB tuples from the decrypted plaintext
    step = 3
    finaltextone=[decrypted[i:i+step] for i in range(0, len(decrypted), step)]
    finaltexttwo=[(int(finaltextone[int(i)])-100,int(finaltextone[int(i+1)])-100,int(finaltextone[int(i+2)])-100) for i in range(0, len(finaltextone), step)]    

    # reconstruct image from list of pixel RGB tuples
    newim = Image.new("RGB", (int(newwidth), int(newheight)))
    newim.putdata(finaltexttwo)
    newim.show()
    
# ---------------------
# GUI stuff starts here
# ---------------------

# empty password alert
def pass_alert():
   tkMessageBox.showinfo("Password Alert","Please enter a password.")
   
def enc_success(imagename):
   tkMessageBox.showinfo("Success","Encrypted Image: " + imagename) 
   
# image encrypt button event
def image_open():
    # useless for now, may need later
    global file_path_e
    
    # check to see if password entry is null.  if yes, alert
    enc_pass = passg.get()
    if enc_pass == "":
        pass_alert()
    else:
        password = hashlib.sha256(enc_pass).digest()
        filename = askopenfilename()
        file_path_e = os.path.dirname(filename)
        # encrypt the image
        encrypt(filename,password)
    
# image decrypt button event
def cipher_open():
    # useless for now, may need later
    global file_path_d
        
    # check to see if password entry is null.  if yes, alert
    dec_pass = passg.get()
    if dec_pass == "":
        pass_alert()
    else:    
        password = hashlib.sha256(dec_pass).digest()
        filename = askopenfilename()
        file_path_d = os.path.dirname(filename)
        # decrypt the ciphertext
        decrypt(filename,password)

# main gui app starts here
class App:
  def __init__(self, master):
    # make passg global to use in functions
    global passg
    # setup frontend titles etc blah blah
    title = "Image Encryption"
    author = "Cahlen Humphreys\ncahlen@gmail.com"
    msgtitle = Message(master, text =title)
    msgtitle.config(font=('helvetica', 17, 'bold'), width=200)
    msgauthor = Message(master, text=author)
    msgauthor.config(font=('helvetica',10), width=200)

    # draw canvas
    canvas_width = 200
    canvas_height = 50
    w = Canvas(master, 
           width=canvas_width,
           height=canvas_height)

    # pack the GUI, this is basic, we shold use a grid system
    msgtitle.pack()
    msgauthor.pack()
    w.pack()
    
    # password field here above buttons
    passlabel = Label(master, text="Enter Encrypt/Decrypt Password:")
    passlabel.pack()
    passg = Entry(master, show="*", width=20)
    passg.pack()

    # add both encrypt/decrypt buttons here which trigger file browsers
    self.encrypt = Button(master, 
                         text="Encrypt", fg="black", 
                         command=image_open, width=25,height=5)
    self.encrypt.pack(side=LEFT)
    self.decrypt = Button(master,
                         text="Decrypt", fg="black",
                         command=cipher_open, width=25,height=5)
    self.decrypt.pack(side=RIGHT)



root = Tk()
root.wm_title("Image Encryption")
app = App(root)
root.mainloop()
Engineering Student
  • 49
  • 1
  • 7

1 Answers1

0

You forgot to close the stream when writing the file. It is better to use the with syntax like this:

with open(cipher_name, 'w') as g: 
    g.write(ciphertext)

It closes the file for you. That way you can be sure that you've written all of the bytes and none are lost.

The same should be done during the read operation.

I haven't checked your code outside of encrypt and decrypt because that is quite a lot of code.

Security considerations:

  • The IV has to be unpredictable for CBC mode, but it doesn't have to be secret. We usually generate a random IV and write it in front of the ciphertext. Since it is always 16 bytes for AES-CBC, you can slice it off during decryption.
  • While your self-made padding scheme (multiple "n" characters) works in this case. It will not work in the general case. Please use something like PKCS#7 padding as seen here.
  • Please use a cipher mode that provides authentication. Otherwise you will not be able to detect (malicious) manipulations of the ciphertext. Examples are seen here.
Artjom B.
  • 61,146
  • 24
  • 125
  • 222