Key control is the ability to control the distribution, duplication, and privilege level of keys in a given keying system. The main focus of key control is protecting the bitting information of keys, limiting the availability of key blanks, and restricting methods of key duplication, even by legitimate users of the keying system.
Add to me!
The ability to duplicate a key for a given system hinders the ability of the keying system to account for working keys and is a major problem for key control. High security locks will provide keys that are mechanically difficult to duplicate without the assistance of special key cutting equipment. Modern key cutting equipment for high security locks will also have secondary measures to prevent arbitrary key bittings from being cut, usually through the use of security cards or an electronic database of customers and their keys.
Do Not Duplicate
Many keys are stamped with "Do Not Copy" (DNC) or "Do Not Duplicate" (DND) to prevent locksmiths from duplicating the key. This warning is rarely backed with legal ramifications and many locksmiths and key duplication centers will duplicate these keys provided they have the proper key blanks.
Restricted Key Profiles
Using a non-standard or custom key profile (the pattern of warding) can provide some measure of key control. Many key profiles are patent protected to prevent them from being manufactured by third parties, making obtaining key blanks more difficult. Many locksmith associations provide members with access to restricted keyways, making key duplication without authorization difficult.
This feature does not prevent a medium to high skill attacker from machining their own key blanks or simulated keys. Several professional machines exist to create key blanks of arbitrary keys either using a working key or a photograph of the key profile. The most notable of these machines is the Easy Entrie.
See Security cards