TLDR: It's a VM that JIT compiles bytecode and runs it to mutate the password/secret. Once you decode the operations it does, you can reverse it via brute force or using z3 (like I did)
Original writeup (with solution script): [https://ctf.harrisongreen.me/2020/hacktm/mama_bear/](https://ctf.harrisongreen.me/2020/hacktm/mama_bear/)