Many of the parts of a land mobile radio communications system will use encryption to protect the information that is sent through the system. The encryption algorithms require keys in order to protect the confidentiality of this information. The process by which these encryption keys are generated, stored, protected, transferred, loaded, used and destroyed is known as key management. These keys must be protected from disclosure and require updating or replacement in order to maintain system security. This is often accomplished manually. However, the most convenient way to do this is by electronically sending keys from a key management facility (KMF) to the destination equipment. This involves sending keys over the air and this procedure is referred to as Over-the-Air-Rekeying (OTAR). OTAR is a method of encrypting and sending the encryption keys and other related key management messages through an air interface in such a way that they are protected from disclosure, and, in some cases, unauthorized modification.

This document describes the basic keying concepts for protected radios, including those fundamental key management concepts related to OTAR. OTAR is an application layer process. Peer processes exist in the key management facility (KMF) and at the mobile radios. The KMF is responsible for providing OTAR functions for the set of mobile radios within its jurisdiction.

The document gives sample operational procedures for the OTAR of radios in a protected system. The interaction between the KMF and mobile radios that is necessary to provide various key management services is described. The operational procedures delineated in this document include both a basic and an advanced set of procedures. No advanced public key OTAR procedures have been defined for Data Encryption Standard applications, and are not discussed in this document. An OTAR protocol document for the particular encryption algorithm being used describes which messages require encryption, message authentication and replay protection.

Customers who purchased TIA TIA-102.AACB
also purchased

• TIA TIA-102.AACA-2 : Project 25 Digital Radio Over-the-Air Rekeying (OTAR) Protocol Addendum 2 – Data Link Independent OTAR-Addendum No. 2 to TIA/EIA-102.AACA
• TIA TIA-102.AABC-C-1 : Project 25 Trunking Control Channel Messages Addendum 1-Addendum to TIA-102.AABC-C
• TIA TIA-102.AABD-A-1 : Project 25 Trunking Procedures Addendum 1-Addendum to TIA-102.AABD-A
• TIA TIA-102.BAAA-A : Project 25 FDMA – Common Air Interface

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