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Add Motorola OTA alias decoding (#2098)

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ilyacodes
2024-12-02 18:31:37 -05:00
committed by GitHub
parent 5c9c3fa503
commit d61d9c07b0
1 changed files with 80 additions and 6 deletions
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86
src/main/java/io/github/dsheirer/module/decode/p25/phase1/message/lc/motorola/MotorolaTalkerAliasComplete.java
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@@ -1,6 +1,6 @@
/*
* *****************************************************************************
* Copyright (C) 2014-2024 Dennis Sheirer
* Copyright (C) 2014-2024 Dennis Sheirer, 2024 Ilya Smirnov
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
@@ -38,6 +38,26 @@ import java.util.List;
*/
public class MotorolaTalkerAliasComplete extends TimeslotMessage implements IMessage
{
private static final byte[] LOOKUP_TABLE =
{
-14, 46, 102, -112, 116, -118, 111, 120, -69, 83, 3, 17, 104, -51, 68, 23,
40, 95, 30, -124, 117, 121, 110, -101, 44, -66, 98, 45, -15, 124, -72, -125,
-39, 78, 109, 2, 97, 61, -88, 6, -71, -8, -100, 55, 58, 35, -63, 80,
-19, -97, -81, 59, -67, -126, -70, -96, -33, -62, 71, 34, -16, -18, -95, -2,
-94, 16, 91, 72, 87, -93, 5, 96, 123, 13, -7, 108, -77, 86, 76, -68,
41, -92, 15, -20, -74, -91, -90, 60, 127, 107, -76, 33, -83, -82, -60, -56,
-59, 93, -34, -32, 29, 25, 75, -58, 12, 63, 90, -57, -31, 89, 85, 84,
74, 67, 66, -30, -29, -6, 0, -28, -27, 24, 65, 11, 10, -26, -4, -3,
-46, -10, -44, 43, 99, 73, -108, 94, -89, 92, 112, 105, -9, 8, -79, 125,
56, -49, -52, -40, 81, -113, -43, -109, 106, -13, -17, 126, -5, 100, -12, 53,
39, 7, 49, 20, -121, -104, 118, 52, -54, -110, 51, 27, 79, -116, 9, 64,
50, 54, 119, 18, -45, -61, 1, -85, 114, -127, -107, -55, -64, -23, 101, 82,
36, 48, 28, -37, -120, -24, -105, -99, 88, 38, 4, 57, -84, 42, -98, -86,
37, -41, -50, -21, -106, -11, 14, -115, -36, -87, 47, -35, 31, -22, -111, -73,
-42, -119, -117, -47, -80, -103, 19, 122, -25, -102, -75, -122, -1, 70, -123, -78,
115, -38, -65, -48, 113, -53, 77, -128, 21, 103, 22, 26, 32, -114, 69, 62
};
private static final IntField SUID_WACN = IntField.length20(OCTET_0_BIT_0);
private static final IntField SUID_SYSTEM = IntField.length12(OCTET_2_BIT_16 + 4);
private static final IntField SUID_ID = IntField.length24(OCTET_4_BIT_32);
@@ -113,9 +133,64 @@ public class MotorolaTalkerAliasComplete extends TimeslotMessage implements IMes
{
if(mAlias == null)
{
//BinaryMessage encoded = getEncodedAlias();
//TODO: implement decoding of the encoded alias.
String alias = "*ALIAS " + getRadio().getValue() + "*"; //Temporary value until we implement decoding
byte[] encoded = getEncodedAlias().toByteArray();
// TODO: check CRC in last two bytes to validate alias has no errors
//
// Data: wwwww sss iiiiii aaaa...aaaa cccc
//
// - w = WACN
// - s = system
// - i = id
// - a = encoded alias
// - c = CRC-16/GSM of the previous bytes
// Get number of bytes and characters excluding checksum
char bytes = (char)(encoded.length - 2);
char chars = (char)(bytes / 2);
// Create array for decoded computed bytes (big-endian)
byte[] decoded = new byte[encoded.length];
// Set up the long-running accumulator
char accumulator = bytes;
char byteIndex = 0;
// Calculate each byte sequentially
do
{
// Multiplication step 1
char accumMult = (char)(((accumulator + 65536) % 65536) * 293 + 0x72E9);
// Lookup table step
byte lut = LOOKUP_TABLE[encoded[byteIndex] + 128];
byte mult1 = (byte)(lut - (byte)(accumMult >> 8));
// Incrementing step
byte mult2 = 1;
byte shortstop = (byte)(accumMult | 0x1);
byte increment = (byte)(shortstop << 1);
while(mult2 != -1 && shortstop != 1) {
shortstop = (byte)(shortstop + increment);
mult2 += 2;
}
// Multiplication step 2
decoded[byteIndex] = (byte)(mult1 * mult2);
// Update the accumulator
accumulator += (char)(((encoded[byteIndex] + 256) % 256) + 1);
byteIndex += 1;
}
while(byteIndex < bytes);
// Copy decoded bytes (as chars) to our alias string
String alias = "";
for (char i = 0; i < chars; i++) {
alias += (char)((decoded[i * 2] << 8) | decoded[i * 2 + 1]);
}
mAlias = P25TalkerAliasIdentifier.create(alias);
}
@@ -192,8 +267,7 @@ public class MotorolaTalkerAliasComplete extends TimeslotMessage implements IMes
mIdentifiers = new ArrayList<>();
mIdentifiers.add(getTalkgroup());
mIdentifiers.add(getRadio());
//TODO: uncomment once alias decoding is implemented.
// mIdentifiers.add(getAlias());
mIdentifiers.add(getAlias());
}
return mIdentifiers;