How Do Bob and Alice and Carol Add Their Encryption Keys To Data?

When I worked as an electrical engineer, we had a hasp to isolate the electric power on a device we were working on:

With this, each person who was working on the equipment, would put on their own padlock, and where we could not put the power back on, until all the padlocks had been taken off. The padlocks could be put on in any order, and taken off in…