Abstract
E2, a 128-bit block cipher, is an AES candidate designed and submitted by NTT corporation. It employs a Feistel structure as global structure and 2-layer Substitution-Permutation Network structure in round function. The conservative structure makes E2 immune to kinds of current cryptanalysis. Previously, there is no result of impossible differential attacks on E2 since it was once supposed to have no more than 5-round impossible differential characteristic. In this paper, the immunity of tweaked E2 (E2 without initial transformation and final transformation) against impossible differential cryptanalysis is evaluated. We present many 6-round impossible differential characteristics of tweaked E2, by using one of which, we perform a 7-round attack on tweaked E2 with 128, 192 and 256 bits key and an 8-round attack on tweaked E2 with 256 bits key. The 7-round attack requires about 2120 chosen plaintexts and 2115.5 7-round encryptions; the 8-round attack needs 2121 chosen plaintexts and less than 2214 8-round encryptions.
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Wei, Y., Yang, X., Li, C., Du, W. (2012). Impossible Differential Cryptanalysis on Tweaked E2. In: Xu, L., Bertino, E., Mu, Y. (eds) Network and System Security. NSS 2012. Lecture Notes in Computer Science, vol 7645. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-34601-9_30
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DOI: https://doi.org/10.1007/978-3-642-34601-9_30
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