Meet-in-the-middle attacks on round-reduced CRAFT based on automatic search

Abstract

CRAFT is a lightweight block cipher designed by Beierle et al. to effectively resist differential fault attacks at fast software encryption 2019. In this article, Demirci-Selçuk meet-in-the-middle (DS-MITM) attacks on round-reduced CRAFT based on automatic search are proposed. A DS-MITM automatic search model for CRAFT was constructed, and then, the automatic search model was used to detect a 9-round DS-MITM distinguisher. The strong relations between the round-subtweakeys were observed and the key-dependent sieve technique was adopted to reduce the memory complexity of the attack. Based on the 9-round distinguisher, a 19-round DS-MITM attack can be presented. Due to the strong key relations, the time complexity can be reduced by the key-bridging technique and the equivalent round-subtweakey. The time complexity of the 19-round DS-MITM attack is 2^114.68 19-round CRAFT encryption, the data complexity is 2⁵⁶ chosen plaintexts, and the memory complexity is 2¹⁰⁹ 64-bit blocks. Adding one round to the end of the 19-round DS-MITM attack, a 20-round DS-MITM attack can be proposed. The time complexity of the 20-round attack is 2^126.94 20-round CRAFT encryption, the data complexity is 2⁵⁶ chosen plaintexts, and the memory complexity is 2¹⁰⁹ 64-bit blocks.