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DMR: Remove Condition where VLC and TLC without FID 0x10 did not calculate RAS MAC attachments; Misc Tweaks to dburst RAS Indicator; #359

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DMR: Tweak FLCO to remove 0x23 as a Cap+ Private Call when it is only a RAS indicator on a normal Private Call; Clarify Comments;

DMR: Tweak RAS MD5 loading to allow for a correction against a flat value (if needed in future based on observation);

DMR: Misc Tweaks to Vertex Standard Key Loading; #316
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lwvmobile
2026-09-06 17:57:42 -04:00
parent fb3dc75c47
commit cd5f0f4a8e
7 changed files with 42 additions and 40 deletions
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41
src/crypt-md5.c
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@@ -410,50 +410,48 @@ void ras_effective_key_creation(dsd_state * state, char * input)
fprintf (stderr, "\n");
//The following rules are still not entirely clear, however,
//the first one executed (last byte) has been observed to be
//true, the SEED values are more speculative, values of
//0 and 0x1F do not change the 5-bit checksum mod 31 (0x1F)
//the last taken digest byte has been observed to be true
//Furthermore, it is still unclear how any rollover is handled,
//if adding 2 is byte inclusive (effectively resetting the byte)
//or if the value is flat 56-bit value and rollover occurs
//to the next value over, using best guess on this
//until further informatin comes along
//against the flat value, using best guess on this
//until further information comes along
//Below patent also suggest all bytes cannot equal zero
//and if so, the next portion of MD5 may be used,
//or some other method may be utilized to prevent fringe cases
//https://patents.google.com/patent/US20130288643A1
//Last Byte low5 not allowed to be 0x1F (reasons unclear, but observed true)
//Last Collected Byte 5-bit LSB not allowed to be 0x1F
if ((ctx.digest[6] & 0x1F) == 0x1F)
{
fprintf (stderr, " Byte %d: %02X -> %02X; ", 7, ctx.digest[6], ctx.digest[6]+2);
fprintf (stderr, " Byte %d: %02X -> %02X; ", 7, ctx.digest[6], (ctx.digest[6]+2) & 0xFF);
ctx.digest[6] += 2;
}
//UPDATE: I have now observed a system that has a 5-bit differential value of 0
//so that means that the low5 effective key value can be either 0, or 0x1F
//collect 7 bytes of the MD5 Hash to create the flat key value
unsigned long long int flat_key = 0;
for (int i = 0; i < 7; i++)
{
flat_key <<= 8;
flat_key |= ctx.digest[i];
}
// //SEED low5 non-zero value (no change to 5-bit EMB checksum mod 31)
// if ((ctx.digest[0] & 0x1F) == 0)
//May switch to this correction method instead if the
//observed rollover is on a flat value and not a byte value
// if ((flat_key & 0x1F) == 0x1F)
// {
// fprintf (stderr, " Byte %d: %02X -> %02X; ", 1, ctx.digest[0], ctx.digest[0]+2);
// ctx.digest[0] += 2;
// }
// //SEED low5 plus 1F (no change to 5-bit EMB checksum mod 31)
// else if ((ctx.digest[0] & 0x1F) == 0x1F)
// {
// fprintf (stderr, " Byte %d: %02X -> %02X; ", 1, ctx.digest[0], ctx.digest[0]+2);
// ctx.digest[0] += 2;
// fprintf (stderr, "Flat Correction: %014llX -> %014llX;\n", flat_key, flat_key+2);
// flat_key += 2;
// }
//byte-reverse the flat_key into the effective_key
unsigned long long int effective_key = 0;
for (int i = 0; i < 7; i++)
{
effective_key <<= 8;
effective_key |= ctx.digest[6-i];
effective_key |= (flat_key >> (i*8)) & 0xFF;
}
uint32_t ras_seed = effective_key & 0xFFFFFFFF;
@@ -467,5 +465,4 @@ void ras_effective_key_creation(dsd_state * state, char * input)
fprintf (stderr, "\n");
}