I was thinking for sometime how it is that we could have a multi-user secure chest for smp so here are two separate ideas I had not sure how feasible either of them are so replies would be nice.
The first was the simple idea of a pad-lock and key. You would create a padlock and use it on one of your own personal-chest and would receive 2 or more keys back. You could then take a key and give it to someone else so they could open the chest so long as they were holding the key when they did. This would be a great way for small groups to have shared secure storage. In the case of this method I would think crafting a key-ring that you can store more than 1 key in so they only take one inventory spot would also probably be a good idea.
Main downside to the above method is that if something happens to all the keys then the original owner would have to break the chest and you would have to redo it all over again to have it a multiuser.
The second idea was the possibility of using a tool like the Freqtrans to add a player’s name to a chest allowing for large groups to have a secure storage and enable the copy and pasting of the chest's memory of who can open it by using said tool to transfer the setting from one to another.
Possible recipe for the pad-lock could be the following: X = bronze 0 = refined iron R = redstone dust
Any and all replies are welcome