Decoding is the process of determining the correct position of components in a lock through manipulation, disassembly, measurement, and observation of keys or lock components. While it does not necessarily open the lock, decoding provides the information necessary to create a working key. In this respect, decoding is the middle ground between lockpicking and impressioning techniques.
Decoding techniques are quite varied and leave a wide range of forensic evidence. Most lock-centric decoding techniques are considered covert because of the invasive manipulation required. In contrast, most key-centric techniques are forms of surreptitious entry because they focus on observation and measurement.
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Decoding via manipulation focuses on invasive manipulation and analysis of the locking components to determine their correct positions. A wide range of tools and techniques exist to determine the number, size, shape, and position of components. In some cases, lockpicking or impressioning is a prerequisite to the decoding process.
- In pin-tumbler locks, a tool may be used to determine bottom pin sizes once the lock has been picked. The tool measures the distance each pin can be raised until it gets to the top of the plug. Tools resemble pin-tumbler picks placed on a lever.
- Sophisticated scales to weigh components to determine their size. Generally, heavier components signify lower depths because of the additional material.
- Tools to count or identify characterstics of components to identify their code.
- Some lockpicking tools, namely axial/tubular picks and the Sputnik tool, automatically decode or impression the lock while it is being picked.
- Impressioning, in a general sense, is a form of manipulation-based decoding that directly produces a working key.
- In combination locks, manipulation of the dial(s), handle, and shackle can be used to determine the correct combination.
Disassembly of the lock will allow direct counts and measurements of internal components. These can be compared with manufacturing data to produce a working key. In some cases, disassembled components are imprinted with their sizes or codes, simplifying the process.
The key is measured to decode the values of the bitting cuts and the keyway profile. Various tools exist for specific locks, such as key gauges, but a ruler or micrometer is equally effective in most cases.
Optical, Photographic, and Visual
Visual observation of a key or lock allows for various forms of decoding.
- Key bitting pattern. This process is known as "sight-reading" a key.
- Key codes on the bow. Can also be used to identify the keyway of a lock.
- Presence and position of secondary locking mechanisms such as sidebars.
In the case of colored lock components, a borescope or similar tool may be used to look inside the lock and determine component positions. Many pin-tumbler rekeying kits use colors to symbolize different bottom pin sizes.
In wafer locks, a borescope or similar tool can be used to look at the position of each wafer as it rests in the lock.
In lever locks, a borescope or similar tool can be used to look at the shape of each lever, but requires that a secondary tool (called a "setup key") be used to move other levers out of the way.
Radiological imaging uses penetrating radiation (X, beta, and gamma rays) to see inside the lock or safe, revealing the proper positions of components. This is most often used against combination locks to determine the position of each gate in the wheel pack. This is a surreptitious entry technique unless the use of such a device can be detected. In many cases, even if the ability to detect this form of entry is available it may be considerably expensive.
The use of low-density wheel materials (such as Delrin) combats this attack. Group 1R safe locks are specifically designed to defeat various radiological attacks as well as provide manipulation protection.