Two Complementary Truncated Differential Attacks on Midori-64

The design of lightweight yet secure block ciphers, particularly for resource-constrained platforms such as RFID tags, tiny sensors, or pocket-sized mobile devices, has been a central focus of symmetric encryption research for over two decades. Midori, introduced by Banik et al. at ASIACRYPT 2015, is one of the most cryptanalyzed lightweight block ciphers and comes in two variants: Midori-64 (64-bit state, 16 rounds) and Midori-128 (128-bit state, 20 rounds), both using a 128-bit key.In this work, we extend the security analysis of Midori-64 via truncated differential techniques, providing a clearer understanding of its resistance against such attacks. We construct two 6-round truncated differentials by precisely computing the propagation probabilities of selected truncated differences through the cipher’s matrix-multiplication layer and tracking their diffusion across rounds. We compute their exact probabilities and use them as distinguishers. By exploiting these two distinguishers, we mount two distinct 10-round truncated differential attacks on Midori-64, representing the first truncated differential attacks reported on the cipher. While the full-round design remains secure, one of our attacks ranks among the best known attacks on 10-round Midori-64.