You’re likely to carry a few keys around on you at any time. A simple piece of metal with a series of notches cut into the blade, or ‘bitting’ of the key. They’re all coded in some way, and locked keys are a regular occurrence. But how did the key come to be locked in the first place, and what is the story behind the bitting of the key?
Locks have pins. These pins are tiny springs that are stuck in a lock’s pin stack. When a key is inserted into a lock, each cut on the key’s blade makes a cut in the coating on each pin in the corresponding pin position. The cut in the coating determines the depth to which the pin is raised. When all the pins are raised to the correct height, the shear line is cleared and the lock’s cylinder turns.
So, a lock with 5 pin positions, each with 5 possible depths for the pins would have 3,125 possible combinations of keys. However, the majority of locks on the market are not set up to produce all of these combinations. Many budget locks have only 3 or 4 depths for the pins, and some are even restricted to prevent the key from being too weak to cut. When a lock is mass produced, it is common for the manufacturer to “tool up” the lock to cut all possible combinations, but this can be very expensive. As a result, many locks are set up to only produce a subset of all possible keys. This is known as the “key space” of a lock, and it is measured in terms of the number of possible keys that could potentially open the lock. Some locks have as few as 200-300 possible keys, yet they may be mass produced and distributed to millions of people. Locksearch databases, as well as other resources such as physical security guidance for homes and businesses, acknowledge that there is a real risk of key duplication, even when all locks are supposedly unique.
This is known as the ‘key-alike’ problem and is a common industrial shortcut where manufacturers create locks with the same bitting to reduce the cost of tooling for true randomness in the key cutting process. Although perfectly legal, this practice is rarely, if ever, disclosed on the packaging of such products.
Master keying adds an extra layer to this problem. As well as the usual number of pin-shear positions found in any lock, a master keyed lock has a second shear position. This means that, in addition to the normal number of cuts required to open a lock in the usual way, a second set of corresponding cuts are required to open the lock with a master key. The problem is, each additional shear position (or pin) increases the potential for another key, by chance, to cut the same combination of cuts.
A good locksmith will always look at the brand of lock and the series of keys that have been issued for your lock. like where the bitting on your key falls in relation to a congested area of the key space or a sparse area of the key space.
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Your key is older than your mobile phone, car, kettle etc. However it may not be as unique.
