Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Add Motorola OTA alias decoding #2098

Merged
merged 1 commit into from
Dec 2, 2024
Merged

Add Motorola OTA alias decoding #2098

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
86 changes: 80 additions & 6 deletions ...ub/dsheirer/module/decode/p25/phase1/message/lc/motorola/MotorolaTalkerAliasComplete.java
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -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
Expand Down Expand Up @@ -38,6 +38,26 @@
*/
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);
Expand Down Expand Up @@ -113,9 +133,64 @@ public P25TalkerAliasIdentifier getAlias()
{
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);
}

Expand Down Expand Up @@ -192,8 +267,7 @@ public List<Identifier> getIdentifiers()
mIdentifiers = new ArrayList<>();
mIdentifiers.add(getTalkgroup());
mIdentifiers.add(getRadio());
//TODO: uncomment once alias decoding is implemented.
// mIdentifiers.add(getAlias());
mIdentifiers.add(getAlias());
}

return mIdentifiers;
Expand Down