Boston Key Party CTF 2017 Cutie Crackme Challenge
(Also known as Qt Crackme, and Cutie Keygenme)
This challenge appeared in BKPCTF 2017. It's a reverse engineering challenge written in Qt with a nice GUI. You have to reverse engineer the algorithm used to verify a key you input.
Solution is in soln. Release is in the .zip. Compile with Qt Creator/QMake.
Some writeups: