Paper 2014/485

An Improved Truncated Differential Cryptanalysis of KLEIN

Shahram Rasoolzadeh, Zahra Ahmadian, Mahmood Salmasizadeh, and Mohammad Reza Aref

Abstract

KLEIN is a family of lightweight block ciphers which proposed at RFIDSec 2011 by Gong et al. It has a 64-bit state and 64, 80 or 96-bit key size which introduce its version. It uses 16 same 4-bit Sboxes combined with two AES's MixColumn transformations for each round. This approach allows compact implementations of KLEIN in both low-end software and hardware. Such an innovative combination attracts the attention of cryptanalysts, and several security analyses have been published. The most successful one was represented in FSE'15 which was a truncated differential attack. They could attack up to 12, 13 and 14 rounds out of total number of 12, 16 and 20 rounds for KLEIN-64, -80 and -96, respectively. In this paper, by finding more efficient truncated differential paths and a slight improving in key recovery method we present two new truncated differential attacks on KLEIN, which recover the full secret key with better time and data complexities for the previously analyzed number of rounds. Also by using these truncated differential paths we are able to attack up to 14 and 15 rounds for KLEIN-80 and -96, respectively, which are the highest rounds ever analyzed.