Security of the AES with a Secret S-Box

  • Tyge Tiessen
  • Lars R. Knudsen
  • Stefan Kölbl
  • Martin M. Lauridsen
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 9054)

Abstract

How does the security of the AES change when the S-box is replaced by a secret S-box, about which the adversary has no knowledge? Would it be safe to reduce the number of encryption rounds?

In this paper, we demonstrate attacks based on integral cryptanalysis which allow to recover both the secret key and the secret S-box for respectively four, five, and six rounds of the AES. Despite the significantly larger amount of secret information which an adversary needs to recover, the attacks are very efficient with time/data complexities of \(2^{17}/2^{16}\), \(2^{38}/2^{40}\) and \(2^{90}/2^{64}\), respectively.

Another interesting aspect of our attack is that it works both as chosen plaintext and as chosen ciphertext attack. Surprisingly, the chosen ciphertext variant has a significantly lower time complexity in the attacks on four and five round, compared to the respective chosen plaintext attacks.

Keywords

AES Integral cryptanalysis Secret S-box 

Notes

Acknowledgements

The work in this paper has partially been funded by the Nasjonal sikkerhetsmyndighet (NSM).

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Copyright information

© International Association for Cryptologic Research 2015

Authors and Affiliations

  • Tyge Tiessen
    • 1
  • Lars R. Knudsen
    • 1
  • Stefan Kölbl
    • 1
  • Martin M. Lauridsen
    • 1
  1. 1.DTU ComputeTechnical University of DenmarkKgs. LyngbyDenmark

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