There is no way to password protect quests reliably. period.

Bottom line is the player still has to decrypt the quest data, without knowing the password.

because of that, the format can be reverse engineered, and an editor that doesn't respect the password can be created.

Opening the source would make that process easier, but it's already been done.

Ripping can't be stopped with a password. cheating can't be stopped with a password. even if it cold be stopped with a password, there's always Cheat Engine. And quest editing can't be stopped wit ha password, even without open source. its' totally pointless. Best to watermark the graphics/audio such that theft can be proven instead.