void decode_key(char *buf, uint32_t *keyret)
{
    char key[4] = { 0 };
    int a = -17;
    int b = 0;
    int c = 3;
    int d = 3;
    int i, j = 15;

    for (i = 0; i < 32; i++) {
        j += a + b + c + 19;

        if (buf[j % 187] & (1 << d))
            key[i / 8] |= 1 << i % 8;

        d = (d + 5) % 8;

        a += 17; if (a >= 51) a = -17;
        b +=  7; if (b >= 28) b = 0;
        c +=  3; if (c >= 33) c = 0;
    }

    memcpy(keyret, key, 4);
}