This specific ransomware actually sounds like a fun task to write oneself. I still remember the iOS filesystem encryption layers of a few years ago, where you had different encryption keys for the two NAND flash layers, the HFS metadata and the per-file encryption. Similarly the OS X FDE is also a bunch of layers of encryption. I bet whoever wrote this had a bit of fun on that task. That said, I really dislike the programmer’s intention in writing that piece of software.