Paper 2022/536
Revamped Differential-Linear Cryptanalysis on Reduced Round ChaCha
Sabyasachi Dey and Hirendra Kumar Garai and Santanu Sarkar and 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 $2^{123.04}.$
Metadata
- Available format(s)
- Category
- Secret-key cryptography
- Publication info
- Published by the IACR in EUROCRYPT 2022
- Keywords
- Stream cipherARXChaChaProbabilistic Neutral Bits (PNBs)Differential attack
- Contact author(s)
- sarkar santanu bir1 @ gmail com
- History
- 2022-05-10: received
- Short URL
- https://ia.cr/2022/536
- License
-
CC BY