void key_decode (const u8 *key, u8 *deckey) {
    u8  seq []   = {6, 0, 2, 9, 3, 11, 1, 7, 5, 4, 10, 8};
    s8  i        = 11;
    u32 v        = 330078017;
    while (i > -1) {
	seq [i] = key [seq [i]];
	if (seq [i] < 8) {
	    seq [i] ^= v & 7;
	    v >>= 3;
	} else
	    seq [i] ^= i & 1;
	deckey [i--] = seq [i];
    }
}