OTAR is the common name for the method of changing or updating encryption keys

Rekeying

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...

 in a two-way radio system over the radio channel (“over the air”). It is also referred to as Over-the-Air Transfer (OTAT), depending on the specific type and use of key being changed.

Many of the newer NSA cryptographic systems that use a 128-bit

128-bit

There are currently no mainstream general-purpose processors built to operate on 128-bit integers or addresses, though a number of processors do operate on 128-bit data. The IBM System/370 could be considered the first rudimentary 128-bit computer as it used 128-bit floating point registers...

 electronic key

Key (cryptography)

In cryptography, a key is a piece of information that determines the functional output of a cryptographic algorithm or cipher. Without a key, the algorithm would produce no useful result. In encryption, a key specifies the particular transformation of plaintext into ciphertext, or vice versa...

, such as the ANDVT

ANDVT

The Advanced Narrowband Digital Voice Terminal is a secure voice terminal for low bandwidth secure voice communications throughout the U.S. Department of Defense. Devices in the ANDVT family include the AN/USC-43 Tactical Terminal , the KY-99A Miniaturized Terminal , and the KY-100 Airborne...

, KY-58

KY-58

The VINSON KY-58 is a secure voice module primarily used to encrypt radio communication to and from military aircraft and other tactical vehicles. It is employed by U.S. Military Joint Services, NATO and some law enforcement agencies. It is designed to operate over bandwidth-restricted circuits...

, KG-84

KG-84

The KG-84A and KG-84C are encryption devices developed by the U.S. National Security Agency to ensure secure transmission of digital data. The KG-84C is a Dedicated Loop Encryption Device , and both devices are General-Purpose Telegraph Encryption Equipment...

A/C, and KY-75, are capable of obtaining new or updated keys via the circuit they protect or other secure communications circuits. This process is known as over-the-air rekey (OTAR) or over-the-air transfer (OTAT). The use of OTAR/OTAT drastically reduces the distribution of physical keying material and the physical process of loading cryptographic devices with key tapes. A station may have nothing to do with actual physical key changeovers on a day-to-day basis. The electronic key would normally come from the Net Control Station (NCS). The added feature of OTAT is that the key can be extracted from an OTAT-capable cryptographic system using a fill device

Fill device

A fill device is an electronic module used to load cryptographic keys into electronic encryption machines. Fill devices are usually hand held and battery operated....

, such as the KYK-13

KYK-13

The KYK-13 Electronic Transfer Device is a common fill device designed by the United States National Security Agency for the transfer and loading of cryptographic keys with their corresponding check word....

  or KYX-15/KYX-15A. The key is then loaded into another cryptographic system as needed.