Practical key recovery attacks on FlexAEAD

Orr Dunkelman, Maria Eichlseder, Daniel Kales, Nathan Keller, Gaëtan Leurent, Markus Schofnegger

Research output: Contribution to journalArticlepeer-review


FlexAEAD is a block cipher candidate submitted to the NIST Lightweight Cryptography standardization project, based on repeated application of an Even-Mansour construction. In order to optimize performance, the designers chose a relatively small number of rounds, using properties of the mode and bounds on differential and linear characteristics to substantiate their security claims. Due to a forgery attack with complexity of 2 46, FlexAEAD was not selected to the second round of evaluation in the NIST project. In this paper we present a practical key recovery attack on FlexAEAD, using clusters of differentials for the internal permutation and the interplay between different parts of the mode. Our attack, that was fully verified in practice, allows recovering the secret subkeys of FlexAEAD-64 with time complexity of less than 2 31 encryptions (with experimental success rate of 75%). This is the first practical key recovery attack on a candidate of the NIST standartization project.

Original languageEnglish
JournalDesigns, Codes, and Cryptography
Issue number4
StateAccepted/In press - 2022

Bibliographical note

Publisher Copyright:
© 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.


  • Authenticated encryption
  • Practical key recovery
  • Truncated differential

ASJC Scopus subject areas

  • Theoretical Computer Science
  • Computer Science Applications
  • Discrete Mathematics and Combinatorics
  • Applied Mathematics


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