In this paper, we propose the efficient and feasible key recovery algorithm against the reduced-round RC6 without whitening,
called RC6W. Our attack applies to a rather large number of rounds. RC6W with r rounds can be broken in a success probability
of 90% by using 28.1r-13.8 plaintexts. Therefore, our attack can break RC6W with 17 rounds by using 2123.9 plaintexts in a probability of 90%.