>>21894110mechanical engineer for 10 years.
there are several ways to accomplish this, but the way it's shown in the picture wouldn't work.
what's shown is a ratchet like a zip tie that she would have to pull perpendicularly to engage the teeth into the grooves.
the issue that reaching straight into the box would not impart any force to close the loop.
instead, I suggest mounting three pulleys to the side of box, one at the top and two at the bottom as part of a moveable block.
the key is attached to a cable running up through the pulleys and to the loose end of the shackle. thus, pulling the key quickly tightens the ratchet at a rate of 2:1 compared to the movement of the key.
the shackle is mounted with a locking cam to sit just below the opening of the box. when the ratchet reaches its tightened state, a notch in the cam allows a capped rod connected to side of the box to be released, allowing the side to flip down. 4x for each of the box sides.
you will have to use slight of hand to pretend to put the loose key in the box
