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DMR: Tweaks to PDU Decryption;

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Allow Manually Loaded Key Value AES on DMR PDU;

Add support for CCR AES-ECB PDU Decryption;
This commit is contained in:
lwvmobile
2025-09-18 12:13:54 -04:00
parent b0a46a541d
commit 99b1fd2fe2
1 changed files with 56 additions and 10 deletions
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66
src/dmr_block.c
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@@ -335,7 +335,7 @@ void dmr_dheader (dsd_opts * opts, dsd_state * state, uint8_t dheader[], uint8_t
//The SAP found here is the actual SAP of the message (like a P25 ndary SAP, and can chain together according to ETSI)
fprintf (stderr, " - SAP %02d [%s] - MFID %02X [%s]", p_sap, sap_string, p_mfid, mfid_string);
//p_sap 1 on mfid 10 (moto) has been observed as the first block of LRRP data (unique fixed format?)
//p_sap 1 on mfid 10 MNIS Header
if (p_mfid == 0x10 && p_sap == 1)
{
//add the header to the first 10 bytes of the storage (sans this header's CRC)
@@ -1007,6 +1007,21 @@ void dmr_block_assembler (dsd_opts * opts, dsd_state * state, uint8_t block_byte
if (memcmp(kaes, empt, sizeof(kaes)) != 0) akl = 1;
}
//if still not akl, see if there is anything manually loaded into K1, K2, K3, K4 instead
if (akl == 0)
{
for (i = 0; i < 8; i++)
{
kaes[i+0] = (state->K1) >> (56-(i*8)) & 0xFF;
kaes[i+8] = (state->K2) >> (56-(i*8)) & 0xFF;
kaes[i+16] = (state->K3) >> (56-(i*8)) & 0xFF;
kaes[i+24] = (state->K4) >> (56-(i*8)) & 0xFF;
}
//if kaes is loaded with a key, then flag on the key loaded variable
if (memcmp(kaes, empt, sizeof(kaes)) != 0) akl = 1;
}
if (R == 0 && state->R != 0) R = state->R;
//easier to manually load up rather than make a loop (RC4)
@@ -1033,8 +1048,13 @@ void dmr_block_assembler (dsd_opts * opts, dsd_state * state, uint8_t block_byte
//generate 128-bit IV from 32-bit MI
//expand 32-bit MI to 128-bit IV for AES mode data decryption
//we only want to do this at the moment of keystream generation
if (alg == 5)
if (alg == 4 || alg == 5)
{
//for the LFSR128d function to show the correct alg
if (state->currentslot == 0)
state->payload_algid += 0x20;
else state->payload_algidR += 0x20;
fprintf (stderr, "\n");
LFSR128d(state);
if (state->currentslot == 0)
@@ -1049,30 +1069,54 @@ void dmr_block_assembler (dsd_opts * opts, dsd_state * state, uint8_t block_byte
decrypted_pdu = 1;
}
if (alg == 5 && akl == 1) //AES-256
else if (alg == 5 && akl == 1 && mi != 0) //AES-256 OFB
{
int nblocks = (state->data_byte_ctr[slot] / 16) + 1;
aes_ofb_keystream_output (maes, kaes, ob, 2, nblocks);
decrypted_pdu = 1;
}
else if (alg == 5 && akl == 1 && mi == 0) //AES-256 ECB (CCR without an IV)
{
//void aes_ecb_bytewise_payload_crypt (uint8_t * input, uint8_t * key, uint8_t * output, int type, int de)
int nblocks = (state->data_byte_ctr[slot] / 16) + 0; //was +1
for (i = 0; i < nblocks; i++)
{
aes_ecb_bytewise_payload_crypt(state->dmr_pdu_sf[slot]+start, kaes, state->dmr_pdu_sf[slot]+start, 2, 0);
start += 16;
}
decrypted_pdu = 1;
}
//other algs available, not sure if others will be used in any DMRA offerings
if (alg == 2 && R != 0) //Tait DES
else if (alg == 2 && R != 0) //Tait DES
{
int nblocks = (state->data_byte_ctr[slot] / 8) + 1;
des_multi_keystream_output (mi, R, ob, 1, nblocks);
decrypted_pdu = 1;
}
if (alg == 4 && akl == 1) //AES-128
else if (alg == 4 && akl == 1 && mi != 0) //AES-128 OFB
{
int nblocks = (state->data_byte_ctr[slot] / 16) + 1;
aes_ofb_keystream_output (maes, kaes, ob, 0, nblocks);
decrypted_pdu = 1;
}
else if (alg == 4 && akl == 1 && mi == 0) //AES-128 ECB (CCR without an IV)
{
//void aes_ecb_bytewise_payload_crypt (uint8_t * input, uint8_t * key, uint8_t * output, int type, int de)
int nblocks = (state->data_byte_ctr[slot] / 16) + 0; //was +1
for (i = 0; i < nblocks; i++)
{
aes_ecb_bytewise_payload_crypt(state->dmr_pdu_sf[slot]+start, kaes, state->dmr_pdu_sf[slot]+start, 0, 0);
start += 16;
}
decrypted_pdu = 1;
}
//NOTE: Observed that keystream should not be applied to pad bytes or CRC
//apply keystream here, only if alg is 1 or 4 AND key is available!
//apply keystream here, only if key is available and keystream created, not ECB.
if (alg == 1 && R != 0)
{
for (i = 0; i < end; i++)
@@ -1084,15 +1128,17 @@ void dmr_block_assembler (dsd_opts * opts, dsd_state * state, uint8_t block_byte
for (i = 0; i < end; i++)
state->dmr_pdu_sf[slot][i+start] ^= ob[i%3096];
}
else if (alg == 4 && akl != 0)
else if (alg == 4 && akl != 0 && mi != 0)
{
for (i = 0; i < end; i++)
state->dmr_pdu_sf[slot][i+start] ^= ob[i%3096];
state->dmr_pdu_sf[slot][i+start] ^= ob[(i+16)%3096];
}
else if (alg == 5 && akl != 0)
else if (alg == 5 && akl != 0 && mi != 0)
{
for (i = 0; i < end; i++)
state->dmr_pdu_sf[slot][i+start] ^= ob[i%3096];
state->dmr_pdu_sf[slot][i+start] ^= ob[(i+16)%3096];
}
//BP key application