Master key

Master Keying

Master keying is a keying system in which more than one key can operate a lock or group of locks. Master keying is commonly used to restrict or allow access to a group of locks in a facility based on a user's access level. Various types of master keying exist depending on the type of lock and the number of access levels required. The use of master keying can have a dramatic effect on the number of real key differs and resistance to various forms of covert entry, such as lockpicking and impressioning.

Master Key Lock Designs

The type of lock will determine what master keying schemes are available. Each lock design has a different method of providing master keying either by adding components, modifying keys, or both.

Combination

Traditional rotary combination locks can have have multiple true gates per wheel, allowing various combinations to be used. The majority of combination locks do not allow master keying without the addition of an auxillary override lock. Electronic combination locks can store a database of valid combinations for different users.

Disc-detainer

Widened or additional true gates on the discs themselves can allow master keying. The high number of key differs in most disc-detainer locks minimizes the threat of key interchange in most systems.

Lever

Various modifications to the levers themselves can allow master keying but most have an adverse effect on security. The majority of real-world lever locks that need to provide master keying do so by providing two keyholes with two sets of levers, or two keyholes with a single set of levers, each lever having two contact points.

Pin-tumbler

Adding additional, smaller pins between the top and bottom pins of each pin tumbler stack allows for additional shear lines to be created. Pin-tumblers provide one of the most versatile master keying solutions.

Wafer

Wafers are modified to have two contact points. The normal (change) key will pick up one set of contact points and master keys the other.

Warded

Warded keys are modified to fit through different warding designs; the locks themselves are rarely modified.

Master Keying Schemes

Interchangeable Cores

A lock that allows user-rekeying by physically removing the cylinder and replacing it with another. Interchangeable core locks usually feature two shear lines which operate independent of one another. One shear line is used to engage the bolt mechansism, and the other to operate the core removal mechanism.

Maison Keying

A master keying system where security is sacrificed to ensure a large number of users can easily access shared resources. This is usually performed by a removal of components or extreme master keying levels, both of which greatly reduce the security of the lock and keying systems. Maison keying is common in older schools and apartment buildings.

Master Rings

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Partial Position Progression

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Rotating Constant Progression System

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Sectional/Multiplex Keyways

A master keying scheme where the keyway profile of a key is used to restrict physical entry of the key to one or more locks. Keys with low levels of access will have key profiles that cannot be inserted into higher level locks. Locks with high levels of access will have most of their warding removed, allowing them to be used in all or most locks in the system. This scheme is most commonly used in addition to traditional master keying schemes, but may be used alone. In warded locks, sectional keyways are the only type of master keying available.

Total Position Progression

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See also

• Key
• Combination
• Lock