I've been working on the encryption for Monster Hunter games for a long time (since Monster Hunter Portable 2nd G). I haven't really spread my code around much but it's always been available on my github and I feel like more people might be interested in it now. Here's my repo dealing with the encryption: https://github.com/svanheulen/mhef It's has code for decrypting/encrypting DLC and saves from Monster Hunter 4 Ultimate and all the the Monster Hunter games from the PSP. Here's my repo for code dealing with the various file formats: https://github.com/svanheulen/mhff The code there is all experimental and not very user friendly but the wiki in that repo has information about the MH4U quest file format which would help you make custom quests. Here's my repo for a proxy server for hosting DLC quests: https://github.com/svanheulen/mhqs/tree/dev The mh4u_proxy.py file is the one for MH4U but it's not user friendly, and you need Twisted. I'll be working on improving it so it's easier for anyone to use. Edit: I made this script much easier to use, please view the README for details. All my code it's licensed under GPLv3. I would love for people to extend my code, make it better, and contribute. Pull requests are always welcome and I'm often available to chat on freenode using the nick svanheulen.