In cryptography, Hierocrypt-L1 and Hierocrypt-3 are block ciphers created by
Toshiba in 2000. They were submitted to the NESSIE project, but were not selected.[3] Both
algorithms were among the cryptographic techniques recommended for Japanese government use by CRYPTREC in 2003, however, both have been dropped to "candidate" by CRYPTREC revision in 2013.
The Hierocrypt ciphers are very similar, differing mainly in block size: 64 bits for Hierocrypt-L1, 128 bits for Hierocrypt-3. Hierocrypt-L1's key size is 128 bits, while Hierocrypt-3 can use keys of 128, 192, or 256 bits. The number of rounds of encryption also varies: Hierocrypt-L1 uses 6.5 rounds, and Hierocrypt-3 uses 6.5, 7.5, or 8.5, depending on the key size.
The Hierocrypt ciphers use a nested substitution–permutation network (SPN) structure. Each round consists of parallel applications of a transformation called the XS-box, followed by a linear diffusion operation. The final half-round replaces the diffusion with a simple
post-whitening. The XS-box, which is shared by the two algorithms, is itself an SPN, consisting of a subkey XOR, an S-box lookup, a linear diffusion, another subkey XOR, and another S-box lookup. The diffusion operations use two MDS matrices, and there is a single 8×8-bit S-box. The key schedule uses the binary expansions of the square roots of some small integers as a source of "nothing up my sleeve numbers".
No analysis of the full ciphers has been announced, but certain weaknesses were discovered in the Hierocrypt key schedule, linear relationships between the master key and some subkeys. There has also been some success applying integral cryptanalysis to reduced-round Hierocrypt variants; attacks faster than exhaustive search have been found for 3.5 rounds of each cipher.
^P. Barreto; V. Rijmen; J. Nakahara Jr.; B. Preneel; Joos Vandewalle; Hae Yong Kim (April 2001). Improved SQUARE attacks against reduced-round HIEROCRYPT. 8th International Workshop on Fast Software Encryption (FSE 2001). Yokohama, Japan: Springer-Verlag. pp. 165–173. doi:10.1007/3-540-45473-X_14.
^Abdelkhalek, Ahmed; AlTawy, Riham; Tolba, Mohamed; Youssef, Amr M. (2015). "Meet-in-the-Middle Attacks on Reduced-Round Hierocrypt-3". Progress in Cryptology -- LATINCRYPT 2015. Lecture Notes in Computer Science. Vol. 9230. Springer International Publishing. pp. 187–203. doi:10.1007/978-3-319-22174-8_11. ISBN 978-3-319-22174-8.
^Sean Murphy; Juliette White, eds. (2001-09-23). "Security evaluation of NESSIE first phase" (PDF). Retrieved 2018-08-12.
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