A master keyed lock system is one in which locks are designed not only to be opened by their individual keys, but also by special “master” keys that open some or all other locks in the system. They are commonly found in commercial, industrial, educational and government facilities as well as in some centrally managed residences. Master keying is used because it allows those who must have access to many locks (maintenance workers, managers, etc.) to carry only a few keys. (Note that master keying is unrelated to whether the locks are sold under the “Master ®” brand name.) It is not usually possible to tell by inspecting a key or a lock from the outside whether it is part of a master system. Individuals should ask their locksmith, building management, or maintenance office whether their locks are master keyed.
This research demonstrates that virtually all master keyed mechanical lock systems are at least theoretically vulnerable; the practical seriousness of the threat to any particular system depends on a number of factors:
- Only master keyed locks are vulnerable to this threat. These techniques are not effective against locks that are not part of a master system.
- In order to make a master key, the attacker must have access to one of the locks in the system and possess or have previously examined its associated key. Any lock and key in the system is sufficient for this purpose, and so any individual who has ever been given access to any key has the potential to carry out the attack. The technique involves a series of simple “probes” of a lock (typically less than fifty) which reveal successively more information about the master key. This can be done in several sessions; continuous access to the lock for an extended period of time is not required.
- The procedure consumes a small number (less than ten) of “blank” keys of the kind that fit the locks. Blank keys for most commonly-used locks are available in small quantities from a wide range of commercial sources. The keys are “cut” using hand-held machines or a small metal file.
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Tags: Locks, master key lock systems