Anyone has the SDK for CRIware for Unity? by saintjejemon at 6:42 AM EDT on April 27, 2016
I guess this SDK would solve the extaction problems for CPKs added as Unity assets, which they included a encryption key. Examples of a game that has CPKs packed in Unity is Fate/Grand Order.
I know this is stupid sounding, but have you tried requesting the SDK download from their site? They seem to give out their SDK pretty freely, from what I've experienced.