ld_pwdgen.c

ld_pwdgen.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>

#if defined(__APPLE__)
#include <libkern/OSByteOrder.h>
#define bswap_16(x) OSSwapInt16(x)
#define bswap_32(x) OSSwapInt32(x)
#else
#include <byteswap.h>
#endif

bool debug = false;

#define rotr32(s, n) (((n) >> s) | ((n) << (32 - s)))

uint32_t sub_1440(uint64_t uid) {
  uint8_t base[] = {
      0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x28,
      0x63, 0x29, 0x20, 0x43, 0x6f, 0x70, 0x79, 0x72,
      0x69, 0x67, 0x68, 0x74, 0x20, 0x4c, 0x45, 0x47,
      0x4f, 0x20, 0x32, 0x30, 0x31, 0x34, 0xaa, 0xaa};

  //Copy UID into structure
  for (int i = 0; i < 7; i++) {
    //Casting to pointer and using subtracted index because
    //the 7 byte uid is stored in a 8 byte type in the reverse
    //order or what I need.
    base[i] = ((uint8_t *)&uid)[6 - i];
  }

  if (debug) {
    printf("i\tv4\tv5\tb\tv2\n");
  }
  uint32_t v2 = 0;
  for (int i = 0; i < 8; i++) {
    int v4 = rotr32(25, v2);
    int v5 = rotr32(10, v2);
    uint32_t b = *(uint32_t *)(base + i * 4);
    v2 = b + v4 + v5 - v2;
    if (debug) {
      printf("[%d] %08x %08x %08x %08x\n", i, v4, v5, b, v2);
    }
  }

  return bswap_32(v2);
}

int main(int argc, char *argv[]) {
  if (argc != 2) {
    printf("%s <7 byte uid in hex>\n", argv[0]);
    return 1;
  }
  uint64_t uid = strtoull(argv[1], NULL, 0x10);
  printf("uid = %014llx => %08x\n", uid, sub_1440(uid));
}