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[Legacy] keys management
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@lyusupov
lyusupov committed May 15, 2024
1 parent 261e591 commit f618bda
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Showing 2 changed files with 88 additions and 21 deletions.
91 changes: 79 additions & 12 deletions software/firmware/source/SoftRF/src/protocol/radio/Legacy.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -140,20 +140,36 @@ long obscure(uint32_t key, uint32_t seed) {
}

static const uint32_t table[12] = LEGACY_KEY1;
static int xxtea_keys_offset = 0;

void make_key(uint32_t key[4], uint32_t timestamp, uint32_t address) {
void make_v6_key(uint32_t key[4], uint32_t timestamp, uint32_t address) {
int8_t i, ndx;
for (i = 0; i < 4; i++) {
if (xxtea_keys_offset == 8) {
ndx = xxtea_keys_offset + i ; /* V7 */
} else {
ndx = ((timestamp >> 23) & 1) ? i+4 : i ; /* V6 */
}
ndx = ((timestamp >> 23) & 1) ? i+4 : i ;
key[i] = obscure(table[ndx] ^ ((timestamp >> 6) ^ address), LEGACY_KEY2) ^ LEGACY_KEY3;
}
}

void make_v7_key(uint32_t key[4]) {
uint8_t *bkeys;
int p, q, x, y, z, sum;

bkeys = (uint8_t *) &key[0];
x = bkeys[15];
sum = 0;
q = 2;

do {
sum += 0x9E3779B9; // "delta"
for (p=0; p<16; p++) {
z = x & 0xFF;
y = bkeys[(p+1) % 16];
x = bkeys[p];
x += ((((z >> 5) ^ (y << 2)) + ((y >> 3) ^ (z << 4))) ^ (sum ^ y));
bkeys[p] = (uint8_t)x;
}
} while (--q > 0);
}

static bool legacy_v6_decode(void *legacy_pkt, ufo_t *this_aircraft, ufo_t *fop) {

legacy_v6_packet_t *pkt = (legacy_v6_packet_t *) legacy_pkt;
Expand All @@ -167,7 +183,7 @@ static bool legacy_v6_decode(void *legacy_pkt, ufo_t *this_aircraft, ufo_t *fop)
int ndx;
uint8_t pkt_parity=0;

make_key(key, timestamp, (pkt->addr << 8) & 0xffffff);
make_v6_key(key, timestamp, (pkt->addr << 8) & 0xffffff);
btea((uint32_t *) pkt + 1, -5, key);

for (ndx = 0; ndx < sizeof (legacy_v6_packet_t); ndx++) {
Expand Down Expand Up @@ -322,7 +338,7 @@ size_t legacy_encode(void *legacy_pkt, ufo_t *this_aircraft) {

pkt->parity = (pkt_parity % 2);

make_key(key, timestamp , (pkt->addr << 8) & 0xffffff);
make_v6_key(key, timestamp , (pkt->addr << 8) & 0xffffff);

#if 0
Serial.print(key[0]); Serial.print(", ");
Expand All @@ -342,28 +358,79 @@ size_t legacy_encode(void *legacy_pkt, ufo_t *this_aircraft) {
*/

bool legacy_decode(void *legacy_pkt, ufo_t *this_aircraft, ufo_t *fop) {
const uint32_t xxtea_key[4] = LEGACY_KEY4;
uint32_t key_v7[4];

legacy_v7_packet_t *pkt = (legacy_v7_packet_t *) legacy_pkt;

if (pkt->type == 0) { /* Air V6 position */
xxtea_keys_offset = 0;
return legacy_v6_decode(legacy_pkt, this_aircraft, fop);
}

xxtea_keys_offset = 8;
uint32_t *wpkt = (uint32_t *) legacy_pkt;
uint32_t timestamp = (uint32_t) this_aircraft->timestamp;

btea(&wpkt[2], -4, xxtea_key);

key_v7[0] = wpkt[0];
key_v7[1] = wpkt[1];
key_v7[2] = timestamp >> 4;
key_v7[3] = 0x956F6C77;

make_v7_key(key_v7);

wpkt[2] ^= key_v7[0];
wpkt[3] ^= key_v7[1];
wpkt[4] ^= key_v7[2];
wpkt[5] ^= key_v7[3];

/* TODO */

return false /* true */;
}

size_t legacy_encode(void *legacy_pkt, ufo_t *this_aircraft) {
const uint32_t xxtea_key[4] = LEGACY_KEY4;
uint32_t key_v7[4];

legacy_v7_packet_t *pkt = (legacy_v7_packet_t *) legacy_pkt;
xxtea_keys_offset = 8;
uint32_t *wpkt = (uint32_t *) legacy_pkt;

uint32_t id = this_aircraft->addr;
uint8_t acft_type = this_aircraft->aircraft_type > AIRCRAFT_TYPE_STATIC ?
AIRCRAFT_TYPE_UNKNOWN : this_aircraft->aircraft_type;
uint32_t timestamp = (uint32_t) this_aircraft->timestamp;

pkt->addr = id & 0x00FFFFFF;

#if !defined(SOFTRF_ADDRESS)
pkt->addr_type = ADDR_TYPE_FLARM; /* ADDR_TYPE_ANONYMOUS */
#else
pkt->addr_type = (pkt->addr == SOFTRF_ADDRESS ?
ADDR_TYPE_ICAO : ADDR_TYPE_FLARM); /* ADDR_TYPE_ANONYMOUS */
#endif

pkt->stealth = this_aircraft->stealth;
pkt->no_track = this_aircraft->no_track;

pkt->aircraft_type = acft_type;

/* TODO */

key_v7[0] = wpkt[0];
key_v7[1] = wpkt[1];
key_v7[2] = timestamp >> 4;
key_v7[3] = 0x956F6C77;

make_v7_key(key_v7);

wpkt[2] ^= key_v7[0];
wpkt[3] ^= key_v7[1];
wpkt[4] ^= key_v7[2];
wpkt[5] ^= key_v7[3];

btea(&wpkt[2], 4, xxtea_key);

return (sizeof(legacy_v7_packet_t));
}

Expand Down
18 changes: 9 additions & 9 deletions software/firmware/source/SoftRF/src/protocol/radio/Legacy.h
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Original file line number Diff line number Diff line change
Expand Up @@ -35,11 +35,11 @@
#define LEGACY_TX_INTERVAL_MIN 600 /* in ms */
#define LEGACY_TX_INTERVAL_MAX 1400

#define LEGACY_KEY1 { 0xe43276df, 0xdca83759, 0x9802b8ac, 0x4675a56b, /* V6 */ \
0xfc78ea65, 0x804b90ea, 0xb76542cd, 0x329dfa32, /* V6 */ \
0xA5F9B21C, 0xAB3F9D12, 0xC6F34E34, 0xD72FA378 /* V7 */ }
#define LEGACY_KEY1 { 0xe43276df, 0xdca83759, 0x9802b8ac, 0x4675a56b, \
0xfc78ea65, 0x804b90ea, 0xb76542cd, 0x329dfa32 }
#define LEGACY_KEY2 0x045d9f3b
#define LEGACY_KEY3 0x87b562f4
#define LEGACY_KEY4 { 0xA5F9B21C, 0xAB3F9D12, 0xC6F34E34, 0xD72FA378 }

/* FTD-12 Version: 7.00 */
enum
Expand Down Expand Up @@ -152,7 +152,7 @@ typedef struct {
typedef struct {
/********************/
unsigned int addr:24;
unsigned int type:4;
unsigned int type:4; /* 2 new protocol, 0 old protocol, 1 other messages */
unsigned int addr_type:3;
unsigned int _unk1:1;
/********************/
Expand All @@ -164,10 +164,10 @@ typedef struct {
unsigned int _unk5:2; /* always 1 ? */
unsigned int _unk6:2; /* always 0 ? */
/********************/
unsigned int _unk9:2; /* always 0 ? */
unsigned int ts:4; /* 4 bits of timestamp (unix epoch) */
unsigned int _unk7:2; /* always 0 ? */
unsigned int ts:4; /* the LS 4 bits of timestamp (unix epoch) */
unsigned int aircraft_type:4;
unsigned int _unk10:1; /* always 0 ? */
unsigned int _unk8:1; /* always 0 ? */
unsigned int alt:13; /* meters + 1000, enscaled(12,1) */

unsigned int lat:20; /* rounded and with MS bits removed */
Expand All @@ -180,8 +180,8 @@ typedef struct {

unsigned int hacc:6; /* meters times 10, enscaled(3,3) */
unsigned int vacc:5; /* meters times 4, enscaled(2,3) */
unsigned int _unk11:5;
unsigned int _unk12:8; /* always 0 ? */
unsigned int _unk9:5;
unsigned int _unk10:8; /* always 0 ? */
/********************/
} __attribute__((packed)) legacy_v7_packet_t;

Expand Down

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