demo-rc4-image.py

#demo XOR RC4
#Yohanes Nugroho 2019
import os
from PIL import Image

key = "YOHANES"
WIDTH=200
HEIGHT=50
IMG1="image1.png"
IMG2="image2.png"
MERGED="image1+2.png"

gentext1 = "convert -size {0}x{1} -background lightblue -fill blue -pointsize 36 -gravity east label:{2} {3}"
gentext2 = "convert -size {0}x{1} -background lightblue -fill blue -pointsize 36 -gravity west label:{2} {3}"

os.system(gentext1.format(WIDTH, HEIGHT, "Yohanes", IMG1))
os.system(gentext2.format(WIDTH, HEIGHT, "Risna", IMG2))

def load_pixels(img):
    im = Image.open(img)
    pixels = im.load()
    width, height = im.size

    all_pixels = []
    for x in range(width):
        for y in range(height):
            r,g,b = pixels[x, y]
            all_pixels += [r,g,b]            
    return all_pixels

def save_pixels(destimage, newpixels):

    background = (0, 0, 0, 255)
    im = Image.new('RGB', (WIDTH, HEIGHT), background)
    width, height = im.size    
    pixels = im.load()    

    for x in range(width):
        for y in range(height):
            r,g,b = newpixels[0:3]
            newpixels = newpixels[3:]
            pixels[x,y] = (r,g,b)
            
    im.save(destimage)
    
#RC4 implementation note
#https://github.com/jbremer/rc4/blob/master/LICENSE.txt
def rc4(data, key):
    """RC4 encryption and decryption method."""
    S, j, out = list(range(256)), 0, []

    for i in range(256):
        j = (j + S[i] + ord(key[i % len(key)])) % 256
        S[i], S[j] = S[j], S[i]

    i = j = 0
    for ch in data:
        i = (i + 1) % 256
        j = (j + S[i]) % 256
        S[i], S[j] = S[j], S[i]
        out.append(0xff & (ch ^ S[(S[i] + S[j]) % 256]))
    return out

def enc_img(image, key):
    pixels = load_pixels(image)  
    enc = rc4(pixels, key)
    save_pixels("enc-"+image, enc)
    return enc

def enc_xor_img(name, enc1, enc2):
    res = []
    for i,j in zip(enc1, enc2):
        res.append(i^j)

    save_pixels(name, res)    

enc1 = enc_img(IMG1, key)
enc2 = enc_img(IMG2, key)

enc_xor_img(MERGED, enc1, enc2)