func ksRotate(in uint32) (out []uint32) {
	out = make([]uint32, 16)
	last := in
	for i := 0; i < 16; i++ {
		// 28-bit circular left shift
		left := (last << (4 + ksRotations[i])) >> 4
		right := (last << 4) >> (32 - ksRotations[i])
		out[i] = left | right
		last = out[i]
	}
	return
}

// creates 16 56-bit subkeys from the original key.
func (c *desCipher) generateSubkeys(keyBytes []byte) {