Rating:
Solution:
We are given this source code:
```
from PIL import Image
from itertools import cycle
def xor(a, b):
return [i^j for i, j in zip(a, cycle(b))]
f = open("original.png", "rb").read()
key = [f[0], f[1], f[2], f[3], f[4], f[5], f[6], f[7]]
enc = bytearray(xor(f, key))
open('enc.txt', 'wb').write(enc)
```
Here we can see that the encryption algorithm used is XORing the original byte array of the image with the first 8 bytes of the image. Since the original image is in PNG format, the first 8 bytes are fixed: 137 80 78 71 13 10 26 10.
By using the property of XOR (A ^ B = C and C ^ B = A), we can decrypt the image by XORing it with these fixed bytes.
Decryption Script:
```
from PIL import Image
from itertools import cycle
def xor(a, b):
return [i^j for i, j in zip(a, cycle(b))]
f = open("enc.txt", "rb").read()
key = [137, 80, 78, 71, 13, 10, 26, 10]
enc = bytearray(xor(f, key))
open('original.png', 'wb').write(enc)
Image.open('original.png').show()
```
```
Flag:
VishwaCTF{h3ad3r5_f0r_w1nn3r5}
```
