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Key (lock)

A key is a device which is used to open a lock. A typical key consist of two parts: the blade, which slides into the keyway of the lock and distinguishes between different keys, and the bow, which is left protruding so that torque can be applied by the user. The blade is usually designed to open one specific lock, although master keys are designed to open sets of similar locks.

Keys provide an inexpensive, though imperfect, method of authentication for access to properties like buildings and vehicles. As such, keys are an essential feature of modern living in the developed world, and are common around the globe. It is common for people to carry the set of keys they need for their daily activities around with them, often linked by a keyring adorned by key fobs and known as a keychain.

Special types of keys

House keys

A house key is the most common sort of key. There are two main forms. The older form is for lever locks, where a pack of flat levers (typically between two and five) are raised to different heights by the key whereupon the slots or gates of the levers line up and permit a bolt to move back and forth, opening or closing the lock. The teeth or bittings of the key have flat tops rather than being pointed. Lever lock keys tend to be bigger and less convenient for carrying, although lever locks tend to be more secure. These are still common in, for example, many European countries.

The more recent form is that for a pin tumbler cylinder lock. When held upright as if to open a door, a series of grooves on either side of the key (the key's profile) limits the type of lock cylinder the key can slide into. As the key slides into the lock, a series of pointed teeth and notches allow pins to move up and down until those pins are in line with the shear line of the cylinder, allowing that cylinder to rotate freely inside the lock and the lock to open. These predominate in, for example, the United States of America.

Car key

A car key or an automobile key is a key used to open and/or start an automobile, often identified with the logo of the car company at the head. Modern key designs are usually symmetrical, and some use grooves on both sides, rather than a cut edge, to actuate the lock. It has multiple uses for the automobile with which it was sold. A car key can open the doors, as well as start the ignition, open the glove compartment and also open the trunk (boot) of the car. Some cars come with an additional key known as a valet key that starts the ignition and opens the drivers side door but prevents the valet from gaining access to valuables that are located in the trunk or the glove box. Some valet keys, particularly those to high-performance vehicles, go so far as to restrict the engine's power output to prevent joyriding. Recently, features such as coded immobilizers have been implemented in newer vehicles. More sophisticated systems make ignition dependent on electronic devices, rather than the mechanical keyswitch. Ignition switches/locks are combined with security locking of the steering column (in many modern vehicles) or the gear lever (Saab Automobile). In the latter, the switch is between the seats, preventing damage to the driver's knee in the event of a collision.

Keyless entry systems, which utilize a remote control in place of a car key, are becoming a standard feature on many new cars. Some of them are handsfree.

Some keys are high-tech in order to prevent the theft of a car. Mercedes-Benz uses a key that, rather than have a cut metal piece to start the car, uses an encoded infrared beam that communicates with the car's computer. If the codes match, the car can be started. These keys can be expensive to replace, if lost, and can cost up to US$400. Some car manufacturers like Land Rover and Volkswagen use a 'switchblade' key where the key is spring-loaded out of the fob when a button is pressed. This eliminates the need for a separate key fob. This type of key has also been known to be confiscated by airport security officials.

Master key

A master key is intended to open a set of several locks. Usually, there is nothing special about the key itself, but rather the locks into which it will fit. These locks also have keys which are specific to each one (the change key) and cannot open any of the others in the set. Locks which have master keys have a second set of the mechanism used to open them which is identical to all of the others in the set of locks. For example, master keyed pin tumbler locks will have two shear points at each pin position, one for the change key and one for the master key. A far more secure (and more expensive) system has two cylinders in each lock, one for the change key and one for the master key.

Larger organizations, with more complex "grandmaster key" systems, may have several masterkey systems where the top level grandmaster key works in all of the locks in the system.

A practical attack exists to create a working master key for an entire system given only access to a single master-keyed lock, its associated change key, a supply of appropriate key blanks, and the ability to cut new keys. This is described in Cryptology and Physical Security: Rights Amplification in Master-Keyed Mechanical Locks

Locksmiths may also determine cuts for a replacement master key, when given several different key examples from a given system.

Control key

A control key is a key used in interchangeable core locking systems. The control key enables the user to remove a core in the cylinder, with a specific combination and replace it with a core with a different combination. In small format interchangeable cores, similar to those developed by Frank Best of the Best Lock Corporation, the key operates a separate shear line, located above the operating key shear line. In other format interchangeable cores, the key may work like a master key along the operating shear line and also contact a separate locking pin that holds the core in the cylinder.

Double-sided key

A double-sided key is very similar to a house or car key with the exception that it has two sets of teeth, an upper level standard set of teeth and a lower, less defined set of teeth beside it. This makes the double-sided key's profile and its corresponding lock look very similar to a standard key while making the attempt to pick the lock more difficult.

Paracentric key

A paracentric key is designed to open a paracentric lock. It is distinguishable by the contorted shape of its blade, which protrudes past the centre vertical line of the key barrel. Instead of the wards on the outer face of the lock simply protruding into the shape of the key along the spine, the wards protrude into the shape of the key along the entire width of the key, including along the length of the teeth. Patented by the Yale lock company in 1898, paracentric cylinders are not exceptionally difficult to pick, but require some skill and know-how on the part of the person attempting to pick the lock.

Skeleton key

A skeleton key (or passkey) is a very simple design of key which usually has a cylindrical shaft (sometimes called a shank) and a single, minimal flat, rectangular tooth or bit. Skeleton keys are also usually distinguished by their bow, or the part one would grasp when inserting the key, which can be either very plain or extremely ornate. A skeleton key is designed to circumvent the wards in warded locks. Warded locks and their keys provide minimal security and only a slight deterrent as any key with a shaft and tooth that has the same or smaller dimensions will open the lock. However, warded keys were designed to only fit a matching lock and the skeleton key would often fit many. Many other objects which can fit into the lock may also be able to open it. Due to its limited usefulness, this type of lock fell out of use after more complicated types became easier to manufacture. In modern usage, the term "skeleton key" is often misapplied to ordinary bit keys and barrel keys, rather than the correct definition: a key, usually with minimal features, which can open all or most of a type of badly designed lock. Bit keys and barrel keys can be newly-minted (and sold by restoration hardware companies) or antiques. They were most popular in the late 1800s, although they continued to be used well into the 20th century and can still be found today in use, albeit in vintage homes and antique furniture. A bit key is distinguished from a barrel key in that a bit key usually has a solid shank, whereas a barrel shafted key can be made either by drilling out the shank from the bit end or by folding metal into a barrel shape when forging the key.

Tubular key

A tubular key (sometimes referred to as a barrel key when describing a vintage or antique model) is one that is designed to open a tubular pin tumbler lock. It has a hollow, cylindrical shaft which is usually much shorter and has a larger diameter than most conventional keys. Antique or vintage-style barrel keys often closely resemble the more traditional skeleton key but are a more recent innovation in keymaking. In modern keys of this type, a number of grooves of varying length are built into the outer surface at the end of the shaft. These grooves are parallel to the shaft and allow the pins in the lock to slide to the end of the groove. A small tab on the outer surface of the shaft prevents the pins in the lock from pushing the key out and works with the hollow center to guide the key as it is turned.

The modern version of this type of key is harder to duplicate as it is less common and requires a different machine from regular keys. These keys are most often seen in home alarm systems, in the United States.

Zeiss Key

A Zeiss key (also known as a Cruciform Key) is a cross between a house key and a tubular key. It has three sets of teeth at 90 degrees to each other with a flattened fourth side. Though this type of key is easy to duplicate, the extra sets of teeth deter lockpicking attempts.

Do Not Duplicate Key

A Do Not Duplicate key (or DND key, for short) is one which has been stamped do not duplicate , duplication prohibited or similar by a locksmith or manufacturer as a passive deterrent to prevent a retail key cutting service from duplicating a key without authorization or without contacting the locksmith or manufacturer who originally cut the key. More importantly, this is a control system for whoever is the owner of the key, such as a maintenance person or security guard, to identify keys that should not be freely distributed or used without authorization. Though it is intended to prevent unauthorized key duplication, copying restricted keys remains a common security problem. There is no direct legal implication in the US for someone who copies a key that is stamped do not duplicate (unless it is a government owned key), but there are patent restrictions on some key designs (see "restricted keys"). The Associated Locksmiths of America calls DND keys "not effective security", and "deceptive because it provides a false sense of security."

United States Code 18 USC Sec. 1704 deals with United States Post Office keys, and 18 USC Sec. 1386 deals with United States Department of Defense keys.

Restricted Key

A restricted keyblank is a keyway and blank for which a manufacturer has set up a restricted level of sales and distribution. Restricted keys are often protected by patent, which prohibits other manufacturers from making unauthorized productions of the key blank. In many jurisdictions, customers must provide proof of ID before a locksmith will duplicate a key using a restricted blank. These days, many restricted keys have special in-laid features, such as magnets, different types of metal, or even small computer chips to prevent duplication.

Keycard

A keycard, while not actually considered a key, is a plastic card which stores a digital signature that is used with electronic access control locks. It is normally a flat, rectangular piece of plastic and may also serve as an ID card. There are several popular type of keycards in use and include the mechanical holecard, bar code, magnetic stripe, smart card (embedded with a read/write electronic microchip), and RFID proximity cards. The keycard is used by presenting it to a card reader; swiping or inserting of mag stripe cards, or in the case of RFID cards, merely being brought into close proximity to a sensor.

Bar code technology is not a secure form of a key, as the bar code can be copied in a photocopier and often read by the optical reader.

Magnetic stripe keycards are becoming increasingly easy to copy, but have the security advantage that one may change the stored key in a magnetic swipe card in case the current key may be compromised. This immediate change of the "key" information can be applied to other media, but this media probably offers the least expensive option, and the most convenient to users and managers of systems that use this media. Example: If you own a car with this system, you can change your keys anytime you want. You can buy new media anywhere a gift card is sold. At least at this point in time, you could buy a gift card for a penny, then use that as the media for the keys to your car. If the system uses digital environmental data samples to create the "key" string, every car can have a set of keys that no one else has. If a card is stolen, or copied without authorization, the card can be remade, and the car security system can be synchronized with the new card, and no longer activationally responsive to the copy of the old card. This approach can empower the system controller (owner/individual or centralized administration of a business).

Computerized authentication systems, such as key cards, raise privacy concerns, since they enable computer surveillance of each entry. Currently RFID cards and key fobs are becoming more and more popular due to its ease of use. Many modern households have installed digital locks that make use of key cards, in combination with biometric fingerprint and keypad PIN options.

The first keycard was the mechanical holecard type patented by Tor Sørnes, a concept he later developed into the magnetic stripe card key.

History of locks and keys

Wooden locks and keys were in use as early as 4,000 years ago in Egypt. It is also said that key was invented by Theodore of Samos in the 6^th century BC.

A machine permitting rapid duplication of flat metal keys, which contributed to the proliferation of their use during the 20th century, may have been first invented in the United States in 1917 (image to the left):

The key to be duplicated is placed in one vise and the blank key to be cut in a corresponding vise under the cutting disk. The vise carriage is then into such position by means of a lateral-feed clutch that the shoulders of both the pattern and blank keys just touch the guide disk and cutter respectively. The lateral-feed clutch on the top of the machine is then thrown, and the vertical feed rod released into action and power applied through the combination hand-crank power wheel on the right of the machine, until the cutter has passed over the entire length at the blank. A duplicate of the pattern key is obtained in about one minute.|10px||"Man And His Machines", The World's Work XXXIII:6 April, 1917

Key duplication in a fashion similar to this is performed in modern times with powered milling or grinding equipment in many retail hardware stores and of course as a service of the specialized locksmith.