Paper 2025/1670
Mixderive: A New Framework of Deriving Linear Approximations and Improved Differential-Linear Distinguishers for ChaCha
Abstract
ChaCha is a well-known ARX-based cipher and has become one of the most widely used ciphers in the real world. In this paper, a systematic three-case framework called \emph{Mixderive} to find linear approximations for ChaCha is proposed. By this new framework, new linear approximations for 3.5- and 4-round ChaCha are found, which are significantly better than the existing linear approximations proposed at EUROCRYPT 2021 and ASIACRYPT 2022. These improvements confirm the effectiveness of \emph{Mixderive}. In addition, new 2- and 2.5-round linear approximations for ChaCha are found by \emph{Mixderive}. Based on these new findings, new differential-linear distinguishers for 7- and 7.5-round ChaCha256 with complexities ${2^{162.28}}$ and ${2^{247.08}}$ are proposed, which improve the best known distinguishers by factors of ${2^{4.61}}$ and ${2^{4.46}}$, respectively. To the best of our knowledge, both cryptanalytic results are the best.
Metadata
- Available format(s)
-
PDF
- Category
- Attacks and cryptanalysis
- Publication info
- Published elsewhere. Major revision. ISPEC 2025
- Keywords
- CryptanalysisLinear approximationDifferential-linear distinguisherChaChaStream cipher
- Contact author(s)
- dinglin_cipher @ 163 com
- History
- 2025-09-18: approved
- 2025-09-15: received
- See all versions
- Short URL
- https://ia.cr/2025/1670
- License
-
CC BY
BibTeX
@misc{cryptoeprint:2025/1670,
author = {Zhengting Li and Lin Ding and Xinhai Wang and Jiang Wan},
title = {Mixderive: A New Framework of Deriving Linear Approximations and Improved Differential-Linear Distinguishers for {ChaCha}},
howpublished = {Cryptology {ePrint} Archive, Paper 2025/1670},
year = {2025},
url = {https://eprint.iacr.org/2025/1670}
}
