skeleton key

A key is a device which is used to open a lock. It usually consists of a specially-shaped piece of flat metal, with cut notches (forming teeth), and/or milled grooves which fit the shape of the lock and can open the correctly combinated lock by (usually) being turned in the lock housing. This portion of the key is referred to as the blade. The wider grip, referred to as the bow, is found at the top of the key to facilitate turning. Usually, there are only a small number of keys which can operate a certain lock. In some residential locks, all of the keys for a lock are given to the purchaser of the lock. Duplicates of the key can normally be made by anyone with the correct key blank and key machine. Some manufacturers assign an identification number to each lock and key combination. Knowing the identification number of such a lock allows a duplicate key to be made at certain places. Many residential keys are identified by the key cuts stamped on the key bow.

Most people in modern society use keys on a daily basis, to secure their home, their vehicle, or to access their workplace, among other uses. Those that use a number of keys will usually place them on a ring or key chain, often with other items such as key fobs.

Special types of keys

House key

A house key is the most common kind of key. When held upright as if to open a door, a series of grooves on either side of the key limits the type of lock cylinder the key can slide into. As the key slides into the lock, a series of notches allow the 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.

Car key

A car key or an automobile key is a key used to open or start an automobile, often identified with the logo of the car company at the head. Modern key designs are usually symetrical, 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. 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.

Master key

A master key is designed to open a set of several locks. 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 and its associated key. This is described in Cryptology and Physical Security: Rights Amplification in Master-Keyed Mechanical Locks

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, a 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. 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 distinguised 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, it has come to describe a key, usually with minimal features, which can open all or most of a type of badly designed lock. Skeleton keys can be newly-minted (and sold by restoration hardware companies) or antiques. True skeleton keys were most popular in the late 1800's, 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 skeleton key is distinguished from a barrel key in that a skeleton 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.

A few car manufacturers such as Ford Motor Company sell skeleton keys (although these are more correctly known as master keys or passkeys) for some of their locks to mechanics in order to aid servicing. This practice is naturally not normally publicized.

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, at least in the United States.

Security on these types of locks are problem, as rediscovered recently. It's known as the "Bic Pen Trick."

Zeiss Key

A Zeiss 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 is one which has been stamped do not duplicate by a locksmith or manufacturer as a deterrent to prevent hardware stores and kiosks from duplicating a key without authorization or without contacting the locksmith or manufacturer who originally cut the key. 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 that copies a key that is stamped do not duplicate, but there are patent restrictions on some key designs (see "restricted 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 often 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.

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

See also

• Advanced key
• Password, Passphrase
• Personal Identification Number
• Personal Unblocking Code
• Key (cryptography)
• Keyway