Over the Air Rekeying (OTAR) is the common name for the method of changing or updating encryption keys 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 electronic key, such as the ANDVT, KY-58, KG-84A/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, such as the KYK-13 or KYX-15/KYX-15A. The key is then loaded into another cryptographic system as needed.