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The system is an APCO25 digital 2-way radio conventional system with repeaters, or it is an APCO25 trunking system.
Motorola Inc. August 1996
English (United States)
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8 -LA Technical Developments
METHOD TO DISCOURAGE UNAUTHORIZED USE OF AN APC025 CONVENTIONAL AND TRUNKED SYSTEM
by Hans Sowa
The.system is an APCO25 digital 2-way radio conventional system with repeaters, or it is an APCO25 trunking system.
An unauthorized user is using an APCO25 dig- ital repeater in a conventional system. Or an unauthorized user is stealing time on an APCOZS trunking system.
All digital voice transmissions will be encrypted by the repeater in the system. So repeater inbound horn a subscriber unit is unencrypted and repeater outbound is encrypted. If an encrypted transmis- sion originates from a subscriber unit, it will be encrypted again by the repeater.
Authorized users in the system will possess the encryption algorithm and encryption key used by
the repeater to encrypt the outbound voice. An unauthorized user will not know the encryption key used.
Unauthorized users who attempt to use the sys- tem will be able to capture the repeater. However, the repeated voice will be unintelligible to the unauthorized user, thus rendering the system use- less to them.
The repeated transmissions will be encrypted with Electronic Codebook, so no encryption syn- chronization (Message Indicator) is necessary. This allows the framing format ofthe digital voice to stay the same when the repeater encrypts the voice. Not all voice information needs to be encrypted, since we are only trying to discourage use of the sys...