Locks and Keys

Locks do not make the chest they’re attached to unbreakable, it will only take longer to be destroyed. You can further increase the security of the chest by enchanting the Lock. Also note that Keys can be enchanted to pick Locks.
 * Locks  can be used to lock Reinforced Chests. Each crafted Key is unique, and can be duplicated or used to craft Locks. Locks are attached by right-clicking a chest, and can be removed by shift-right-clicking with a fitting Key.
 * Keys are used to unlock Locks that were placed on Reinforced Chests.  Keys  can be enchanted, giving them extra protection or abilities.

Source : http://minecraft-big-dig-pack.wikia.com/wiki/Better_Storage