A lock is a mechanical or electronic fastening device that is released by a physical object (such as a key, keycard, fingerprint, etc.), by supplying secret information (such as a number or letter permutation or password). There are many types of locks such as the combination lock or the deadbolt lock, but the most common type of lock is the pin tumbler lock.
Pin Tumbler Locks
First of all, let’s talk about the outside part of this type of lock. The outside part is the case. The part inside of that is the plug. The opening part inside the plug is the keyway. That is the part where the key is inserted in.
Inside, there are a few more parts. Through the keyhole, there are many vertical shafts that goes through the keyhole. Each shaft has a spring, a driver pin, and a key pin.
The top part is the spring, then the driver pin, and finally the key pin is the part that goes in contact with the key parts.
The springs press all the pins down so that they all rest on a ledge. You’ll notice that the pins meet at a different level for each shaft. For the plug to turn, the pins must line up with the Shear line.
What if the wrong key is inserted?
The pins will not lined up, which means the the Plug won’t rotate. When we insert the correct key, everything lines up, and the Plug turns.
So, we’ve covered the case of one key for one lock; there’s another case.
Let’s say there’s a building where there’s a different key for each door, but there’s also a key that opens every single door in the building. This is called a Master key. For the Master key to work, there must be an extra pin in at least one of the Vertical Shafts. We call this the Master pin. Now the plug will turn if there is a key that raises the pins either to the 1st pin or the 2nd pin in that shaft. Both the normal key and the master key allows the lock to open. Some master key systems will have more than one Shaft with a Master pin.
Where to get more information about different locks
Pin Tumbler locks
https://en.wikipedia.org/wiki/Pin_tumbler_lock
