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Refactor how blocks are generated to be cleaner

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This commit is contained in:
DarkMatterMatt 2021-02-11 14:07:14 +13:00
commit 03347fcfea
1 changed files with 21 additions and 14 deletions
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35
client/src/cmdlfgallagher.c
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@ -187,6 +187,16 @@ static int CmdGallagherReader(const char *Cmd) {
return PM3_SUCCESS;
}
static void setBitsInBlocks(uint32_t *blocks, uint8_t *pos, uint32_t data, uint8_t data_len) {
for (int i = data_len - 1; i >= 0; i--) {
uint8_t blk = *pos / 32;
uint8_t bitPos = 31 - *pos % 32; // fill from left
uint8_t bit = (data >> i) & 1;
blocks[blk] |= bit << bitPos;
(*pos)++;
}
}
static void createBlocks(uint32_t *blocks, uint8_t rc, uint16_t fc, uint32_t cn, uint8_t il) {
// put data into the correct places (Gallagher obfuscation)
uint8_t arr[8] = {0};
@ -202,7 +212,7 @@ static void createBlocks(uint32_t *blocks, uint8_t rc, uint16_t fc, uint32_t cn,
// more obfuscation
scramble(arr, ARRAYLEN(arr));
// every byte has a 9th bit which is the inverse of the last bit
// every byte is followed by a bit which is the inverse of the last bit
uint8_t bonus_bit[8] = {0};
for (int i = 0; i < ARRAYLEN(bonus_bit); i++) {
bonus_bit[i] = !(arr[i] & 0x1);
@ -211,19 +221,16 @@ static void createBlocks(uint32_t *blocks, uint8_t rc, uint16_t fc, uint32_t cn,
// calculate checksum
uint8_t crc = CRC8Cardx(arr, ARRAYLEN(arr));
// magic prefix, then the 9-bit bytes, then the CRC
blocks[0] = (0x7fea << 16)
| (arr[0] << 8) | (bonus_bit[0] << 7)
| (arr[1] >> 1);
blocks[1] = ((arr[1] & 0x1) << 31) | (bonus_bit[1] << 30)
| (arr[2] << 22) | (bonus_bit[2] << 21)
| (arr[3] << 13) | (bonus_bit[3] << 12)
| (arr[4] << 4) | (bonus_bit[4] << 3)
| (arr[5] >> 5);
blocks[2] = ((arr[5] & 0x1f) << 27) | (bonus_bit[5] << 26)
| (arr[6] << 18) | (bonus_bit[6] << 17)
| (arr[7] << 9) | (bonus_bit[7] << 8)
| crc;
blocks[0] = blocks[1] = blocks[2] = 0;
uint8_t pos = 0;
// magic prefix, then the bytes with their extra bit, then the CRC
setBitsInBlocks(blocks, &pos, 0x7fea, 16);
for (int i = 0; i < ARRAYLEN(arr); i++) {
setBitsInBlocks(blocks, &pos, arr[i], 8);
setBitsInBlocks(blocks, &pos, bonus_bit[i], 1);
}
setBitsInBlocks(blocks, &pos, crc, 8);
}
static int CmdGallagherClone(const char *Cmd) {