Teisybe's Blog

So I have this friend Alex. He is one of the best programmers that I know and had the honor to work with. The guy literally lives and breathes bits and bytes. He is also a fan of programming challenges, especially optimization ones. Sometimes he creates his own. One day, he dropped me a file on Discord titled floppy.img and said “solve it”. I put it off for some time due to a busy schedule and that was a grave mistake on my part, because this is the most fun crackme that i’ve solved to date.

This is a write-up of a crackme titled cracknkeygen by 0xdecaf for Linux which can be found on crackmes.one. On crackmes.one, this crackme has a difficulty score of 2.0. Tools used while solving this crackme are Ghidra and Python. The binary expects the user to pass in the key via the first argument as such: ./cracknkeygen <key>. Upon execution, it either prints a success or failure message. Our task is to figure out how the key is checked and write a key generator to generate valid keys for this binary.