Keyhole Block is a custom item made especially for Blackblock.
The Keyhole Block can emit a redstone signal when the correct key is used on it.
This is the Keyhole's GUI.
The top slot is where you can put your Passport
When a Keyhole has a Passport, only the owner of that passport will be able to open the GUI again.
(To make sure nobody can just craft the same key and pick your lock, you should Engrave the key.)
On the bottom row you have to insert Operation Cards. Currently only the Increment Output Operation Cards are supported. It'll make the Keyhole block emit a redstone signal. 1 card will output a redstone signal of 1, 15 cards will emit a redstone signal of 15.