[aidenn0]

> * Basic keyholders getting masterkeys by taking locks apart. Think of a college dorm where they want every resident to be able to open the front door, but not each others' dorm rooms, and they want the fire department to have one key that will work for all the rooms. Because of the way masterkey systems work, a resident can take the lock off their dorm room door, measure some internal components, and figure out the cuts on the fire department master key. Restricted key blanks make this a lot harder.

You can actually do it without disassembling the lock with N+1 keyblanks (where the lock has N pins).

Master keys work by having two[1] setpoints for each pin. So you copy your key N times, leaving a different pin uncut in each copy. Then just slowly file down the key until it unlocks. It will unlock in the pin-set position for your key and the pin-set position for the master key. This allows decoding the master key position for a single pin.

Finally, copy the master-key positions onto the last keyblank.

Basically it lets you turn a M^N problem (M positions, N pins) into a MN problem.

1: Assuming the non-master keys are random, there's a chance the two setpoints will be the same on any given pin/lock.