Results of switching-closure-test on FEAL
The closure tests, CCT and MCT, were introduced to analyze the algebraic properties of cryptosystems by Kaliski et al. [KaRiSh]. If a cryptosystem is closed, the tests give the same results “Fail” and the cryptosystem might be breakable. Though CCT requires much less memory and time than MCT, we cannot apply CCT to check cryptosystems having the same data and key block lengths such as FEAL with non-parity mode. Because CCT utilizes the differences in data and key block lengths.
Though CCT experiments performed by Kaliski et al. detected that DES is not closed, how should FEAL be checked? Does FEAL pass in MCT? Since MCT needs a lot of memory and time, to check FEAL, we developed a switching closure test SCT [MoOhMi], which is practical version of MCT. In this paper, by using SCT, it is confirmed that FEAL is not closed with high probability.
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