Cryptology ePrint Archive: Report 2021/224

Improved Linear Approximations to ARX Ciphers and Attacks Against ChaCha

Murilo Coutinho and T. C. Souza Neto

Abstract: In this paper, we present a new technique which can be used to find better linear approximations in ARX ciphers. Using this technique, we present the first explicitly derived linear approximations for 3 and 4 rounds of ChaCha and, as a consequence, it enables us to improve the recent attacks against ChaCha. Additionally, we present new differentials for 3 and 3.5 rounds of ChaCha that, when combined with the proposed technique, lead to further improvement in the complexity of the Differential-Linear attacks against ChaCha.

Category / Keywords: secret-key cryptography / ChaCha ARX secret-key cryptography differential linear cryptanalysis

Original Publication (in the same form): IACR-EUROCRYPT-2021

Date: received 27 Feb 2021

Contact author: murilo coutinho at redes unb br

Available format(s): PDF | BibTeX Citation

Version: 20210302:202715 (All versions of this report)

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