Using Multiplex Key Systems

Aug. 1, 2007
The strength of a multiplex key system is that it can drastically increase the power of a mater key system. The weakness is that many keyways are readily available

Commercial locks are designed to limit the types of keys that can enter the lock cylinder.

This is accomplished by uniquely slotting the plug component within the lock cylinder. This unique slot is the “keyway.” The keyway allows a predictable subset of different key shapes to be properly inserted into the plug. Each of the different key shapes is a “key section.”

Some keyways accommodate a single key section while other keyways are strategically widened to allow whole groups (or families) of key sections, to access the plug.

The main application for keyways having more than one key section is to enhance or expand the number of change key possibilities for a master key system.

Creating and machining sectional keyways is part mathematics and part artistry. The keyways require precise machining. The keyway must be accommodating enough to allow all the intended key sections while being restrictive enough to limit unauthorized key sections.

Keyways are slotted into the lock cylinder plug, primarily using broaching tools. The broach is a hardened piece of tool steel that features graduated heights of teeth. As the broach is forced into the brass plug, the slot widens until the width meets specification. The complexity of the keyway is determined by different broaches that are run through the plug.

Basic key blanks are stamped out of flat stock and then run through several milling steps. Each step relieves more of the key until the specified overall profile is accomplished.

Most lock companies design their lock cylinder components including the plugs to be interchangeable. If a lock cylinder needs to be rekeyed to a different key section, a new plug can sometimes be ordered and retrofitted into the lock cylinder.

Multiplex Key Systems

A finite number of change keys are available in a two-step quadratic master key system. In a 10-depth, five-pin system the yield is 1024; and in a six-pin system it is 4096. With large and multiple buildings, these numbers may not be sufficient.

Lock companies can provide lock cylinders with keyways whose profiles can accommodate specific keyways, while limiting other keyways within the associated group (or family) of key sections.

Figure 5 is an example an example of a “multiplex” key system. Each different key section in the family can support an entire (but parallel) master key system.

In a multiplex key system there are multiple levels of access. Each higher level is thinner, enabling it to pass more or different keyways.

The “all-section” key blank for the multiplex key system in Figure 5 is identified as GST.

On the left of Figure 5 is the hierarchy of key sections; on the right is the GST key section overlaid in red, onto each key section. The black areas not covered by the red reveal the remainder of the keyway not filled by the GST key section.

A standard 10-depth six-pin system has 4096 change keys. Each of these key sections (in Figure 5) can yield 4096 change keys: GA; GB; GC; GD; GE; GF; GG; and GH. That produces 32,768 change keys.

Multi-section keys in the multiplex key system are: GAH; GBG; GCE; and GDF. GAH sections can access GA and GH; GBG sections can access GB and GG; GCE sections can access GC and GE; and GDF can access GD and GF.

Lock cylinders can be ordered for multi-section GAH; GBG; GCE; and GDF keyways. This provides for even more expansion as each of these key sections can also support a key system.

The GMK level can access GAH; GBG; GCE; and GDF. Again lock cylinders can be ordered with a GMK keyway. Only the GMK and GST sections can access GMK keyways.

Here is a typical example how multiplex key systems are used. Buildings at a college campus are each setup to different single-section keyways: GA; GB; GC; GD; GE; GF; GG; and GH. All custodial closets are keyed alike. The custodian's key operates in a given building that uses GD keyways would have a change key cut on a GD key blank. A custodian that works in all buildings would have the same key combination cut on a GMK key blank.

Figure 6 is a Schlage multiplex key system that features a “composite” keyway that all single-section key blanks can access.

A composite keyway is enlarged to accept more than one key section. This provides for an additional level of master keying. Composite keyways should be used in areas where low security is required.

A practical example using this level is where restrooms in all buildings would be keyed alike and locks would feature composite keyways. Any custodian in any building could open or close a restroom in any building.

Note that the keyways in Figure 6 are identified as “obverse” keyways. Obverse or open keyways are those that are available without ordering formalities. This means that these are available to all locksmiths, directly from their distributors, without questions asked.

Here is a practical example of how a locksmith can use obverse keyways. A client has a site with 90 suites, all keyed to a master key. The client wants a new administration suite keyed off the master key, but still the manager needs to carry a single key. If all the suites use a “C” keyway, the administration suite can be keyed using “E” keyway lock cylinders and a new master key cut for the manager on an “CE” key blank. Although the CE is not considered a master key, the use of the CE provides greater expansion capability by reserving the “H” key blank. The new master key will open all suites including the new administration suite.

This multiplex key system in Figure 7 was introduced in 1959 and incorporates the single-section keyway 60, which replaced 77 as Corbin's stock keyway in 1960.

It is common that different families of key sections will mirror other existing key sections. Figure 8 is an example where broaching and milling tools were reversed to produce one family of keyways for one company and an opposite for the other. This is preferred as development of new key sections relies on new sets of tools which are expensive to originate.

Protecting Key Stock

The inherent weakness of master key systems is the availability of others to obtain key stock. As master key systems are enhanced by multiplexing; protecting key stock becomes especially important.

Lock companies are sensitive to this and provide multiplex key systems with different levels of key control. Open (or obverse) systems allow any locksmith to obtain key stock; restricted systems are controlled by the company or distributor; and security systems require special arrangements between company and customer to obtain key stock.

There was a time in which companies that provide key stock to locksmiths would not provide key blanks identified by lock companies as restricted. Starting in the late 60s, key shops started carrying aftermarket key blanks for older restrictive systems. By the late 70s it was common place to see popular restrictive key blanks in key shops.

A typical means for lock companies to protect the ornamentality of a key blank is to protect it with a design patent. In an effort to protect the keyway, lock companies started including the keyway profile in the design patent.

Functionality vs. Ornamentality

In 1996, Best Lock had their design patent 327,636 made invalid.

Best Lock started a campaign in which they initiated individual design patents for 33 original keyways. In this manner the keyways could not be reproduced for aftermarket use.

Best Lock sued Ilco-Unican Corp., when the company distributed aftermarket key blanks with similar keyways. Best Lock lost the lawsuit when the design patent that protected the keyways was made invalid. The court decided that the profile of the keyway was much more functional than ornamental. Design patents protect the ornamentality of the invention. Where an invention can be ornamental and functional, keyways are very specific and based almost entirely on being functional.

Best Lock's submittals were very specific. The title of each design patent was: “the portion of a key blank” (basically the keyway), and claims focused on the precise shape. This was all about functionality.

Losing this case was monumental as it allowed companies that provide aftermarket key blanks to reproduce formally protected keyways and distribute them without restrictions. Lock companies could no longer rely on design patents to guarantee their exclusive rights to distribute restricted keyways.

Lock companies went back to the drawing board and designed new key blanks that were not only instrumental in operating the lock cylinder, but were also necessary to disable additional security features.

New key blanks would sport cavities, detents, dimples, and insertions. These new features would engage security mechanisms within the lock cylinder. The key blank and lock cylinder would be protected by utility patents that focused on functionality.

High Security Multiplex Key Systems

High security multiplex key systems were then created where all keys in the system feature the protected invention.

Lock companies now offer large multiplex key systems integrated with security features that are protected with strong utility patents. Figure 12 is an example where all the keys in this multiplex key system are protected by patent from being reproduced and distributed by others.

The Keymark® keyway, shown in Figure 13, uses a security leg® that is set at an angle. By changing the angle of the security leg®, a new set of proprietary keyways can be developed. Wards along the security leg® allows keyways that share an angle to be multiplexed.

An additional feature of Keymark® cylinders is that several versions are available to accommodate retrofitting into all kinds of commercial locksets and padlocks.

A Bit Of Irony

Today companies are looking for exclusive keyways that work with their master key systems and will guarantee that the distribution of key stock is kept secured.

Modern exclusivity is based upon the purchase of new high-security lock cylinders that feature multiplex key systems.

An alternative is to research older, obsolete keyways.

Lock companies like Corbin, Schlage and Yale, have been around for a long time and they still have the ability to provide lock cylinders, plugs, and key blanks with old, obsolete or rare keyways.

Some of these keyways are so old or rare that aftermarket key blanks were never made or were discontinued.

A key blank has to be popular to justify the expense of tooling up for an aftermarket version.

Ironically, old, obsolete, or rare keyways provide significant security as it is not practical to “knock” them off, leaving the lock company as the only means to obtain key stock.