I am not an expert, but I am assuming some of the decrypting needs to get certain info from their servers. Also DVDFab verifies your license is valid each time it launches (one of the things it does is compare your current mac address(es) of your network adapter(s) with what it has on record the last time you authorized the app. (This is why you should do a de-authorization when changing network adapters (or computers), then re-authorize after the change is made, which will require you to enter your current username and password linked to your account and app.) Without verifying your license each time, unlicensed non-legitimate copies could easily be passed around. Many apps today use license verification when launching. If it can't verify, then it starts up in a limited free trial version.
