Welcome to the resource topic for 2022/536
Title:
Revamped Differential-Linear Cryptanalysis on Reduced Round ChaCha
Authors: Sabyasachi Dey, Hirendra Kumar Garai, Santanu Sarkar, Nitin Kumar Sharma
Abstract:In this paper, we provide several improvements over the existing differential-linear attacks on ChaCha. ChaCha is a stream cipher which has 20 rounds. At CRYPTO 2020, Beierle et al. observed a differential in the 3.5-th round if the right pairs are chosen. They produced an improved attack using this, but showed that to achieve a right pair, we need 2^5 iterations on average. In this direction, we provide a technique to find the right pairs with the help of listing. Also, we provide a strategical improvement in PNB construction, modification of complexity calculation and an alternative attack method using two input-output pairs. Using these, we improve the time complexity, reducing it to 2^{221.95} from 2^{230.86} reported by Beierle et al. for 256 bit version of ChaCha. Also, after a decade, we improve existing complexity (Shi et al: ICISC 2012) for a 6-round of 128 bit version of ChaCha by more than 11 million times and produce the first-ever attack on 6.5-round ChaCha$128$ with time complexity 2^{123.04}.
ePrint: https://eprint.iacr.org/2022/536
Talk: https://www.youtube.com/watch?v=XIYDz8hObNw
Slides: https://iacr.org/submit/files/slides/2022/eurocrypt/eurocrypt2022/306/slides.pdf
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