Thoughts On Master Keying

With the introduction of electronic locks many years ago, some locksmiths predicted that by this time all metal keys would be extinct. Nothing could be further from the truth.


Specifically in the automotive industry we have seen continuing progress in the reduction and elimination of mechanical keyed cylinders. Fewer and fewer cars each year have keyed cylinders in the trunk, doors or glove box. Even the keyed ignition switch is disappearing. In the commercial and...


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In a fully progressed system each chamber uses all of the cuts available in that manufacturer’s system. In most common 10-depth, two-step systems the cuts range from a shallowest cut of 0 to a deepest cut of 9 for a total of 10 available depths. (Illustration #3)

The two-step means that for each given cut of the master key, every other available cut is used in the progression of the system. If a MK cut is an even number in the first chamber, all cuts used in the first chamber will be even. In a chamber with odd cuts in the MK all individual cuts used in that chamber must also be odd. Since we will have five available cuts in each (even or odd) chamber and one is used in the master key, we have a progression value of 4. A mathematical formula dictates that 4 is the prime number in progression.

Determining The KBA

The Key Bit Array (KBA) is also known as the Progression Chart. The first step is to determine the cuts of the master key. After the cuts of the master key are chosen, each chamber can be progressed out. In a partially progressed system, some chambers are progressed and some remain constant. Carrying constants reduces the number of available cuts. (Illustration #4)

Since each chamber offers four possible cuts, the number of cuts in each chamber is multiplied by the number of cuts in the next chamber. The more chambers progressed, the more cuts available. Progressing three chambers will result in 64 cuts (4x4x4) and leave three chambers to be used as constants. In common use, this is considered a one page system with 4 columns of 16 cuts each. Expanding progression to four chambers will give you four pages of 64 cuts each with a total of 256 cuts (4x4x4x4). Remember the exponential formula, the number of shear lines in a chamber times the number in the next chamber.

Therefore a fully progressed 10-depth, two-step system will give you a maximum of 4096 cuts because all chambers are progressed (4x4x4x4x4x4) or 4 to the sixth power. (Illustration #5)

Common Areas

One of the biggest problems faced is that of the common area. Whenever a building is master keyed, the issue of shared entry doors, bathrooms, etc. is raised.

People all have a key to their own doors but don’t want to carry an extra key for the common areas. Loading a cylinder with a low bottom pin and a stack of master wafers or pins can cause lock problems with jammed pins or keys working when they shouldn’t. A 6-pin lock with that setup can actually have thousands of shear lines! Almost any key inserted will open the lock.

Security is tighter when a totally separate key is issued for those doors. Explain to your customer the risks involved and the loss of security.

When it is necessary, here are a couple of ideas to minimize problems and keep security as tight as possible. By keying only the first and last chambers of the lock in a system carrying constants in those chambers, a key with specific cuts will be required to gain entry.

In a 5-pin system, use a 6-pin housing and utilize the sixth chamber. Fully insert a 5-pin key from the system and insert the proper length pin in the sixth chamber to achieve a shear line. The point of the pin will actually rest on the slope of the tip of the key. This will ensure that any key used from the system must be fully inserted into the lock before it will operate.

Decoding An Existing System

When you take over a new building from a customer, there is usually an existing MK system in place. If the customer doesn’t have a copy of the charts, you don’t have the KBA or progression information. You also don’t have the number of cuts used, unused or what key was issued for what door.

Aside from gaining access to the information from the previous locksmith servicing this account or a total re-key, you may be able to determine a lot of the missing information from what is at hand. This is not a slam-dunk guarantee, but it can certainly help. The problem is that it takes time and effort.

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