OTAR

During encrypted radio conversations REGULAR KEY CHANGING of the code used in scramblers/encryptors is of vital importance.

Regular key changing is one of the basic requirements for secure radio communication.
Key changing can be achieved by reprogramming of scramblers with a wired programmer or over the air.
Presently radio communication systems, secured by scramblers, prefer to use the OTAR  (Over-The-Air-Rekeying) method of key changing.

This method is more effective than programming by means of a wired programmer. Without OTAR to change the keys of all the radios you have to collect all radios to reprogram or a technician must must visit all the radio sites with a PC and programmer in the shortest possible time just to change keys. Very often it is very difficult or even impossible due to their big number and distances of one from another.  Due to this, leading manufacturers of scramblers began to design various methods of key changing over the air that were abbreviated OTAR.

Naturally, there is no common standard of OTAR technology as there is not a single common standard for voice encryption devices. AT Communications has developed its own OTAR protocol (signalling) as an additional option for its digital encryption modules. Our OTAR protocol is user friendly, protected from interception and/or modification by possible eavesdroppers.

Digital modules with the OTAR function are additionally abbreviated with "SOB" (Subscriber-Otar-Basic) and simultaneously support two signalling protocols:
- dispatcher system DS control and administration protocol (control function Check, complete block function (Kill in case of loss or theft of the radio, interception mode Listen, temporary restriction of radio for receiving or transmitting Restrict, silence mode, etc.) and
- protocol of key changing over the air OTAR-Basic.

OTAR basic features:

• manual input of voice keys (non-automatic) by dispatcher
• key changing takes place in real time and individually only
• key management messages (KMM) are encrypted by an individual key
• protection of KMM from interception, message delayed repeat and distortion of information
• encryption of signalling protocol to exclude traffic analysis (PTT-ID, Check, Emergency, etc)

System D with OTAR includes:

• dispatcher (security manager)
• personal computer PC
• software OBS
• controller CBR-DOB
• base radio

Users

• digital modules SOB
• radios