On the Statistically Optimal Divide and Conquer Correlation Attack on the Shrinking Generator

The shrinking generator is a well-known key stream generator composed of two LFSR’s, LFSRx and LFSRc, where LFSRx is clock-controlled according to the regularly clocked LFSRc. In this paper we investigate the minimum required length of the output sequence for successful reconstruction of the LFSRx initial state in an optimal probabilistic divide and conquer correlation attack. We extract an exact expression for the joint probability of the prefix of length m of the output sequence of LFSRx and prefix of length n of the output sequence of the generator. Then we use computer simulation to compare our probability measure and two other probability measures, previousely proposed in [5] and [3], in the sense of minimum required output length. Our simulation results show that our measure reduces the required output length

An Improved Truncated Differential Cryptanalysis of KLEIN

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\u27s 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\u2715 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

On the Statistically Optimal Divide and Conquer Correlation Attack on the Shrinking Generator

The shrinking generator is a well-known key stream generator composed of two LFSR’s, LFSRx and LFSRc, where LFSRx is clock-controlled according to the regularly clocked LFSRc. In this paper we investigate the minimum required length of the output sequence for successful reconstruction of the LFSRx initial state in an optimal probabilistic divide and conquer correlation attack. We extract an exact expression for the joint probability of the prefix oflengthmof the output sequence of LFSRx and prefix oflengthnof the output sequence of the generator. Then we use computer simulation to compare our probability measure and two other probability measures proposed in [5] and [3] in the sense of minimum required output length. Our simulation results show that our measure reduces the required output length