November 16, 2006 6881094C31-E
3-42 Theory of Operation: Encryption Module
The radio power-down sequence begins by opening the radio On/Off switch, which removes the
B+SENSE signal from the VOCON board. This does not immediately remove power because the
GCAP II IC has control of Q502 through Vref, and U301 through WDI maintains the GCAP II IC in an
active state. Both the MCU and Flipper IC monitor B+SENSE. After B+SENSE is removed, the
Flipper IC waits 125 ms. before releasing WDI to allow for software cleanup; however, the software
has the ability to prolong this time if it was necessary to complete its operations. When WDI is
released, the GCAP II IC shuts down its supplies and the rest of the radio through Q501. In
NNTN5567 VOCON board, the radio power-down sequence begins by opening the radio On/Off
switch, causing the MECH_SW pin to transition high. This causes the MAKO IC to start an internal
125ms watchdog timer and drive the INT_X interrupt output pin low. The dual-core processor then
determines (through communication on the SPI bus) that it must initiate the power-down sequence.
At this point, the watchdog timer can be kept alive by the dual-core processor (via the SPI bus)
allowing for software cleanup. Upon expiration of the watchdog timer, the MAKO IC asserts the
RESETX pin and turns off all DC regulators including SW_B+ (Q500 turns off when the MAKO IC
drives the FET_ENX pin high).
3.3 Encryption Module
The encryption module (secure models only) connects directly to the VOCON board and interfaces
directly with the vocoder digital circuitry. It contains an independent microcontroller and two custom
ICs to perform digital, numerical, encryption algorithms.
The encryption modules are designed to digitally encrypt and decrypt voice and ASTRO data in
ASTRO XTS 5000 radios. This section covers the encryption modules, hardware kits NTN9738 and
NNTN5032.
NOTE: The encryption modules are NOT serviceable. The information contained in this section is
only intended to help determine whether a problem is due to a encryption module or the radio
itself.
The encryption module uses a custom encryption IC and an encryption key variable to perform its
encode/decode function. The encryption key variable is loaded into the encryption module, via the
radio's universal (side) connector, from a hand-held, key variable loader (KVL). The encryption IC
corresponds to the particular encryption algorithm purchased. Table 3-6 lists the encryption
algorithms and their corresponding kit numbers.
The encryption module operates from two power supplies (UNSW_B+ and SW_B+). The SW_B+ is
turned on and off by the radio's On/Off switch. The UNSW_B+ provides power to the encryption
module as long as the radio battery is in place.
Table 3-6. Encryption Module Software Kits and Algorithms
Software
Kit Number
Algorithm
NNTN4006 DES, DES-XL, DES-OFB
NTN9837 DES, DES-XL, DES-OFB WITH DVP-XL
NTN9838 DVI-XL
NTN9839 DVP-XL
NNTN4197 AES
NNTN4198 AES with DES, DES-XL, DES-OFB
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