This addendum specifies a method to transport Over The Air Rekeying (OTAR) Key Management Messages (KMMs) between a Key Management Facility (KMF) and an Mobile Radio (MR) that is independent of the physical and data transport layers. It defines optional key management procedures for Registration and Deregistration of the MR with the KMF. An Unable-To-Decrypt message has also been defined to respond to a message that was received and could not be decrypted. The addendum supplements the information contained in the TIA/EIA 102.AACA APCO Project 25 Over-The-Air-Rekeying (OTAR) Protocol document (reference [1]) and in TIA/EIA 102.AACA-1 Key Management Security Requirements For Type 3 Block Encryption Algorithms (reference [2]).

To allow for data link independent transport of KMMs, the encryption synchronization (ESYNC) has been appended to the beginning of the KMM and is included as part of the data packet. The method defined in the addendum may be used with any KMM that is defined in the OTAR Protocol standard (reference [1]).