Over the Air Rekeying

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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. Although the acronym refers specifically to radio transmission means, the technology is also employed via land line and cable.

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.

OTAR technology and methods were operationally introduced to the US Department of Defense by the U.S. Navy in 1991 through 1993. Lieutenant Commander David D. Winters, Naval Communications Security Officer for the European Theater (on the staff of the Commander in Chief, US Navy Europe) early recognized the necessity for these advances and personally oversaw development and deployment of the innovative procedures required for incorporating OTAR throughout the Navy. Shortly thereafter, when joint US forces became heavily tasked in the Middle-East and Eastern Europe, Commander Winters was dispatched promptly to the combat zones, providing opportunity to introduce these same capabilities to the Air force, Army, and Allied forces.

This revolutionized US and associated military telecommunications security by eliminating the previous requirements for risky, expensive wide-spread distribution of paper code keys. It thereby extinguished vulnerability to physical theft and loss previously exploited by the infamous Jonathan Walker spy ring.[1] Elimination of this vulnerability, although little appreciated outside the security community at the time, was an innovation of inestimable impact.

Winters's contributions were quietly recognized and mentioned in official history,[2] military awards and by his election in 2003 to membership in the elite British Special Forces Club.[3]


  1. ^ See John Anthony Walker.
  2. ^ "OPERATION PROVIDE COMFORT, A Communications Perspective, published by the United States European Command Directorate of Command, Control, and Communications, June 4, 1993.
  3. ^ See Special Forces Club