Cyber Apocalypse 2021

Authenticator

Solved by chronocruz.exe

• Disassembling the binary using IDA we get the first code block

• Here we can clearly see the “Alien ID: “ that is supposed to be the first input

• To find the pin, we proceed down the code flow

• We can see there’s a function named “checkpin” being called so we look at what its doing

• It may get slightly difficult to understand what this code really means..
• We can use decompilers like Ghidra to try to convert this into something we can understand better.

• Looking at the decompiled “checkpin” function, we can clearly see a XOR operation on a string.
• It’s safe to say that our pin must be the XOR of each character in this string with 9.
• With the help of this simple Python script we print the flag