Given a custom made hash, the task is to break it (find a collision). The flaw lies in fact that only the first 4 bytes used from md5sum for every round for hl/hr. This could be easily break, thus it has dozens of right answer. More on [original post](https://catousify.wordpress.com/2018/02/04/sharifctf-2018-fhash-writeup/).

Original writeup (https://catousify.wordpress.com/2018/02/04/sharifctf-2018-fhash-writeup/).