DACS App Note

Encrypted Radios in Model Builder version 4.06 (#47)

Model Builder versions 4.06 and higher enhance the encrypted mode operation of the radio objects. A library of crypto tones can be associated with each model and crypto system of a given radio object. This library greatly simplifies the encrypted radio simulation by automatically playing tones (such as a preamble, a postamble, or a mismatch tone) at the appropriate times during a secure radio transmission or reception. In earlier versions of Model Builder, the user had to trigger individual playsounds to simulate these tones.

Overview

Radio objects in Model Builder version 4.06 and higher contain several crypto parameter fields: crypto key, crypto system, crypto preamble, and crypto tone gain. The crypto key is a four byte integer that is assigned to the entire radio object (i.e. it applies to all radio modes) but can be changed dynamically. The crypto system is a four byte integer that is assigned to each individual radio mode. The crypto preamble is a library of sound files that are designated to play at specific points during a secure radio transmission or reception within a given radio mode. The crypto tone gain is a floating point value that controls the gain level of all of the crypto tone sound files. The following discussion assumes that the standard radio environment parameters (e.g. frequency, modulation type, system, frequency hopping parameters) match between radios. If these parameters do not match, secure communication will not occur regardless of how the crypto parameters are set.

Crypto Key

This field appears on page four of the radio object as shown in the figure below. The value of this field is set through a control variable which is offset by a fixed value. The crypto key provides discrimination among radios operating in secure mode. If the crypto key is zero, encrypted communication will not occur. If the crypto keys in the transmitting and receiving radios do not match, the receiving radio will not receive the encrypted transmission. The hexadecimal value $FFFF acts as a wildcard value. A transmission from a radio with a wildcard crypto key, will be received by any radio with a nonzero crypto key and a matching or wildcard crypto system value (see Crypto System below). Likewise, a radio with a wildcard crypto key, will receive transmissions from any radio with a nonzero crypto key and a matching or wildcard crypto system value.

Screen shot

Crypto System

The crypto system field appears on page four of the radio object for each of the eight radio modes. This field is set to a fixed value. Like the crypto key, the crypto system provides discrimination among radios operating in secure mode. However, unlike the crypto key which applies to the entire radio object, each crypto system value applies to the specific radio mode to which it is assigned. If the crypto system is set to zero for a given radio mode, encrypted communication will not occur in that radio mode. If the crypto system in the transmitting and receiving radios do not match, the receiving radio will not receive the encrypted transmission. The hexadecimal value $FFFF is a wildcard for the crypto system just as it is for the crypto key. A transmission from a radio mode with a wildcard crypto system, will be received by any radio with a matching or wildcard crypto key and a nonzero crypto system value. Likewise, a radio in a mode with a wildcard crypto system, will receive transmissions from any radio with a matching or wildcard crypto key and a nonzero crypto system value.

The enumerated values that the DIS protocol uses in the Crypto-System field of the transmitter PDUs for certain radio crypto systems are shown in the table below.

Field Value Radio Crypto System
0 Other
1 KY-28
2 KY-58
3 Narrow Spectrum Secure Voice (NSVE)
4 Wide Spectrum Secure Voice(WSVE)
5 SINCGARS ICOM

Crypto Preamble

The crypto preamble field appears next to the crypto system field on page four of the radio object. This field contains a library of sound files and is individually assigned to each radio mode. The sound file library is simply a sound group whose sound files have particular indices. The sound file index is specified within the sound file object as shown in the figure below. This index controls when that sound file is played during encrypted communication between radios. The duration of the sound file is also controlled within the sound file object through the "Begin Posn" and "End Posn" fields.

Screen shot

The table below explains each index value and under what conditions a sound file with that index is played.

Name Index Play Conditions
RX Crypto Preamble 1 -1 Played at receiving radio when crypto key and crypto system of transmitting and receiving radios match (through actual values or wildcards)
RX Crypto Preamble 2 -2 Played at receiving radio after the first preamble when crypto key and crypto system of transmitting and receiving radios match (through actual values or wildcards)
RX Crypto Postamble -3 Played at receiving radio at the end of a transmission when crypto key and crypto system of transmitting and receiving radios match (through actual values or wildcards)
RX Crypto TX Clr -4 Played at receiving radio when either crypto key or crypto system is zero at the transmitting radio and crypto key and crypto system are nonzero at the receiving radio.
RX Crypto Match -5 Played at receiving radio during the entire transmission after preambles when crypto key and crypto system of transmitting and receiving radios match (through actual values or wildcards).
RX Crypto No Match -6 Played at receiving radio during entire transmission when crypto key and crypto system of transmitting and receiving radios do not match
TX Crypto Preamble 1 -21 Played at transmitting radio when crypto key and crypto system of transmitting radio are nonzero
TX Crypto Preamble 2 -22 Played at transmitting radio after first preamble when crypto key and crypto system of transmitting radio are nonzero
TX Crypto Postamble -23 Played at transmitting radio at the end of a transmission when crypto key and crypto system of transmitting radio are nonzero
TX Crypto TX Clr -24 Played at transmitting radio when either crypto key or crypto system is zero
TX Crypto On -25 Played at transmitting radio during entire transmission after preambles when crypto key and crypto system are nonzero

Crypto Tone Gain

The crypto tone gain field appears next to the crypto preamble field on page four of the radio object. This field controls the output gain of all of the sound files in the crypto sound library. The crypto tone gain can be set to a fixed value only.