06080337

a

06080337 Asano, Yuki Yanagihara, Shingo Iwata, Tetsu Cryptanalysis of 256-bit key HyRAL via equivalent keys. Bao, Feng (ed.) et al., Applied cryptography and network security. 10th international conference, ACNS 2012, Singapore, June 26--29, 2012. Proceedings. Berlin: Springer (ISBN 978-3-642-31283-0/pbk). Lecture Notes in Computer Science 7341, 257-274 (2012). 2012 Berlin: Springer EN cryptanalysis blockcipher HyRAL equivalent key

doi:10.1007/978-3-642-31284-7_16

Summary: HyRAL is a blockcipher whose block size is 128 bits, and it supports the key lengths of 128, 129,$ \cdots $,256 bits. The cipher was proposed for the CRYPTREC project, and previous analyses did not identify any security weaknesses. In this paper, we consider the longest key version, 256-bit key HyRAL, and present the analysis in terms of equivalent keys. First, we show that there are $2^{51.0}$ equivalent keys (or $2^{50.0}$ pairs of equivalent keys). Next, we propose an algorithm that derives an instance of equivalent keys with the expected time complexity of $2^{48.8}$ encryptions and a limited amount of memory. Finally, we implement the proposed algorithm and fully verify its correctness by showing several instances of equivalent keys.