User's Manual

Table Of Contents
MM102558V1 R1A
5.4.3 Advanced Encryption Standard
Advanced Encryption Standard (AES) is a block cipher format approved for use as an encryption standard
by the U.S. government. AES is fast in both software and hardware, is relatively easy to implement, and
requires little memory. AES is currently used in conjunction with the P25 technology.
Unlike DES, AES operates as a substitution-permutation network. AES utilizes fixed blocks of data
formed into tables. AES has a fixed block size of 128 bits and a key size of 128, 192 or 256 bits. AES
uses a process of shifting data in a table. The bit shifting techniques are known as AddRoundKey,
SubBytes, ShiftRows and MixColumns. This combination of block data, bit shifting and unique key
driven encryption methodologies provide much further advanced encryption capabilities than DES or
VGE.
5.5 P25 CONVENTIONAL CONFIGURATIONS
VHF and UHF MASTR III ADC stations may be equipped with a DSP Module to allow operation as a
Project 25 (P25) Conventional station. P25 compliant stations use four-level FM modulation (C4FM),
and are backward compatible with traditional analog FM radios. P25 Conventional technology supports
the following modes of communication:
P25 Conventional Base Station (4-Level FM)
P25 Conventional Repeater
P25 Conventional Repeater with Console Control
P25 is an Industry Standard developed to bring Interoperability between different manufacturers, and
users of their respective digital communications equipment. P25 technology uses a standardized digital
format known as Common Air Interface (CAI). CAI incorporates various system information and a
digital voice format into one digital transmission.
While the DSP card located in the MASTR III ADC station provides the P25 formatting, external
equipment is required to encrypt the voice product delivered to the station. External encryption
equipment for P25 Conventional systems is available for three types of encryption:
DES
VGE
AES
The encryption formats are discussed in Section
5.4.
5.5.1 P25 Conventional Station Operation
MASTR III ADC stations operating in P25 Conventional mode utilize additional circuitry in the RX IF
Module to provide the properly filtered and amplified signal required by the DSP Module to decode the
signal. The DSP Module also provides the encoded C4FM signaling for the transmitter.
In the 21.4 MHz RX IF module (VHF and UHF stations), the 455 kHz four-level FM signal passes
through additional IF filtering, a differential amplifier, and a buffer to the 455kHzIF lines on the
backplane. Unlike 2-level signals, the signals present on the 455kHzIF lines are not demodulated. These
lines connect to the DSP Module input where the DSP captures the data signal and processes it as
necessary.
During TX operations, the DSP Module encodes the inbound audio or digital signal into the P25
compliant C4FM modulation scheme and routed via the backplane to the TX Synthesizer Module.
29