Date : Thu , 15 Apr 1999 22 : 17 : 28 + 0900 ( JST )

This paper studies the security offered by E2 against truncated differential attack. At FSE’99, Matsui and Tokita presented a paper on this. They showed a possible attack on an 8round variant of E2 without IT and FT -Functions. To check their results and confirm that the full E2 is secure against this type of cryptanalysis, we developed a search algorithm to find all byte characteristics that lead to possible attacks on E2. As a result, we found another possible attack on an 8-round variant of E2 without IT or FT -Function with less complexity. Moreover, we found that it is possible to distinguish a 7-round variant of E2 with IT and FT Functions from a random function. However, no flaw in the full E2 has been discovered by this type of cryptanalysis.