> Picking apart r0B's Sanssu crackme

(12/17/2025), 1 minute read ⏰

Note: these are just my markdown notes, but a bit cleaned up. The original sample link is there too! Feel free to check out the original notes here!

This crackme is a 64-bit C/C++ Windows binary. This was a bit rough for me, since this was my first crackme after doing some practice w/ OALabs tutorials. I did in fact cheat and look at a writeup. In the process of such, my analysis became a lot smoother.

The complete markdown note for my analysis can be found here, though this was a pretty short analysis!

With all that being said, I will quickly summarize the functionality of this program!

The program takes input from the user through a message box. The message's length must be >= 5 AND <= 11, and the key itself must be an odd number. If it wasn't incredibly clear yet, yes, we do need to write a keygen given the checks for a bad key. The logic for checking a bad key involves some string magic, which I didn't solve (but should, because that's how a true engine ear should think!) I still had my share of fun with this challenge. If I did want to write a keygen, then I would simply just write an equivalent C program and begin fuzzing away w/ characters until I get a good key (then you can write a keygen!)

The link to the author for the writeup I consulted is here. They went into a LOT more depth than I did and I encourage you to check them out for a good look into making a keygen for this crackme.

That's all I have to share. Thanks for reading, and have a good rest of your day!