1  Category: #Reversing 
 2  Rated Difficulty: #VeryEasy 
 3  Personal Difficulty: #Easy 
 4  
 5  Open [[.elf]] file in [[Binary Ninja]]
 6  
 7  Reading through the function we can see that it uses [[ChaCha20]] and the key it uses to generate the ciphertext.
 8  
 9  Use the key to decrypt the flag.txt.undead and get the flag
10  
11  **OR**
12  
13  Rename the flag.txt.undead by removing the .undead there is a function to detect for .undead and not encrypt it.
14  
15  Since there is no nonce set, if we run the hash through the algorithm again, we will get the plaintext