Theoretical Analysis of "Correlations in RC6"

In this paper, we give the theoretical analysis of χ attack proposed by Knudsen and Meier on the RC6 block cipher. To this end, we propose the novel method of security evaluation against χ attack precisely including key dependency by introducing a technique “Transition Matrix Computing.” On the other hand, the way of security evaluation against χ attack has not been known except the computer experiment. We should note that it is the first results the way of security evaluation against χ attack is shown theoretically. Using this method, we can obtain the “weakest keys” against the attack. Keyword: RC6, χ attack, Transition Matrix,