Here‘s a cool challenge by Ryscrow of Root-Me . The challenge says
For this challenge you will need to decypher a simple XORed picture. This BMP picture was mistakenly encrypted. Can you recover it ?
The file name is “ch3.bmp” and let’s open in a hex editor and see. I first inspected the first 20 bytes and we can see a string saying “fallen”. Actually I guessed this key of length 6.