Paper 2022/1351

Better Steady than Speedy: Full break of SPEEDY-7-192

Christina Boura, Université Paris-Saclay, UVSQ, CNRS, Laboratoire de mathématiques de Versailles, 78000, Versailles, France
Nicolas David, Inria France
Rachelle Heim Boissier, Université Paris-Saclay, UVSQ, CNRS, Laboratoire de mathématiques de Versailles, 78000, Versailles, France
Maria Naya-Plasencia, Inria France

Differential attacks are among the most important families of cryptanalysis against symmetric primitives. Since their introduction in 1990, several improvements to the basic technique as well as many dedicated attacks against symmetric primitives have been proposed. Most of the proposed improvements concern the key-recovery part. However, when designing a new primitive, the security analysis regarding differential attacks is often limited to finding the best trails over a limited number of rounds with branch and bound techniques, and a poor heuristic is then applied to deduce the total number of rounds a differential attack could reach. In this work we analyze the security of the SPEEDY family of block ciphers against differential cryptanalysis and show how to optimize many of the steps of the key-recovery procedure for this type of attacks. For this, we implemented a search for finding optimal trails for this cipher and their associated multiple probabilities under some constraints and applied non-trivial techniques to obtain optimal data and key-sieving. This permitted us to fully break SPEEDY-7-192, the 7-round variant of SPEEDY supposed to provide 192-bit security. Our work demonstrates among others the need to better understand the subtleties of differential cryptanalysis in order to get meaningful estimates on the security offered by a cipher against these attacks.

Available format(s)
Secret-key cryptography
Publication info
A minor revision of an IACR publication in EUROCRYPT 2023
Differential cryptanalysisBlock ciphersSPEEDYSecurity claimKey recovery
Contact author(s)
christina boura @ uvsq fr
nicolas david @ inria fr
heim rachelle @ gmail com
maria naya_plasencia @ inria fr
2023-02-21: last of 6 revisions
2022-10-10: received
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Creative Commons Attribution


      author = {Christina Boura and Nicolas David and Rachelle Heim Boissier and Maria Naya-Plasencia},
      title = {Better Steady than Speedy: Full break of SPEEDY-7-192},
      howpublished = {Cryptology ePrint Archive, Paper 2022/1351},
      year = {2022},
      note = {\url{}},
      url = {}
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