Optimal differential trails in lightweight block ciphers ANU and PICO

摘要

Abstract ANU and PICO are two lightweight block ciphers published by Bansod et al. in 2016. For cryptanalysis, we apply a branch-and-bound based search algorithm to find the least number of active Substitution boxes (S-boxes) in differential trails of these ciphers. Designers provide a lower bound on the number of active S-boxes in any differential trail of ANU up to 4 rounds as 0, 2, 8, and 20. We improve this lower bound to 0, 2, 5, and 9. We present the optimal differential trails in ANU for 7 rounds with probability . The design specification of PICO claims to generate a large number of active S-boxes in a few rounds. We reduce the lower bound on the number of active S-boxes in any 6-round trail from 12 to 6. We also present the optimal differential trails in PICO for 21 rounds with probability . These are the best results reported in the literature for differential cryptanalysis of ANU and PICO.