Rekeying normally refers to the ability to change a lock so that a different key may operate it. Rekeying is done when a lock owner may be concerned that unauthorized persons have keys to the lock, so the lock may be altered by a locksmith so that only new keys will work. Rekeying is the relatively simple process of changing the tumbler or wafer configuration of the lock so a new key will function while the old one will not. Rekeying is done without replacement of the entire lock.
Rekeying was first invented in 1836 by Solomon Andrews, a New Jersey locksmith. His lock had adjustable tumblers and keys, allowing the owner to rekey it at any time. Later in the 1850s, inventors Andrews and Newell patented removable tumblers which could be taken apart and scrambled. The keys had bits that were interchangeable, matching varying tumbler configurations. This arrangement later became the basis for combination locks.
Roughly equivalent to the classical procedure of changing codes on a daily basis, the key is changed after a pre-set volume of data has been transmitted or a given period of time has passed.
In contemporary systems, rekeying is implemented by forcing a new key exchange, typically through a separate protocol like Internet key exchange (IKE). The procedure is handled transparently to the user.
A prominent application is Wi-Fi Protected Access (WPA), the extended security protocol for wireless networks that addresses the shortcomings of its predecessor, WEP, by frequently replacing session keys through the Temporal Key Integrity Protocol (TKIP), thus defeating some well-known key recovery attacks.