Paper 2021/224

Improved Linear Approximations to ARX Ciphers and Attacks Against ChaCha

Murilo Coutinho and T. C. Souza Neto


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.

Available format(s)
Secret-key cryptography
Publication info
Published by the IACR in EUROCRYPT 2021
Contact author(s)
murilo coutinho @ redes unb br
2021-09-22: revised
2021-03-02: received
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Creative Commons Attribution


      author = {Murilo Coutinho and T.  C.  Souza Neto},
      title = {Improved Linear Approximations to ARX Ciphers and Attacks Against ChaCha},
      howpublished = {Cryptology ePrint Archive, Paper 2021/224},
      year = {2021},
      note = {\url{}},
      url = {}
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