Cryptology ePrint Archive: Report 2020/350

New Multi-bit Differentials to Improve Attacks Against ChaCha

Murilo Coutinho and T. C. Souza Neto

Abstract: The stream cipher ChaCha is an ARX type algorithm developed by Daniel Bernstein in 2008. Since its development, ChaCha has received a lot of attention and is currently being used in several systems. The most powerful cryptanalysis of reduced versions of this cipher was presented by Choudhuri and Maitra on FSE 2017 by using differential-linear cryptanalysis. In their work they show that is possible to obtain linear relations between bits from different rounds with high probability and use the proposed equations to create multi-bit differentials and improve previous attacks. In this work, we provide new linear approximations that can be used in a similar fashion but with increased efficiency. Therefore, we show that using these new equations is possible to improve the attacks against 6 and 7 rounds of ChaCha.

Category / Keywords: secret-key cryptography / cryptanalysis, stream ciphers, ChaCha, differential linear cryptanalysis, probabilistic neutral bits

Date: received 24 Mar 2020

Contact author: murilo9988 at gmail com,tsouzaneto@gmail com

Available format(s): PDF | BibTeX Citation

Version: 20200326:074805 (All versions of this report)

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