Method of Security Evaluation of the LBlock-like Ciphers against Differential Cryptanalysis

Authors

  • Oleksii Yakymchuk National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, Ukraine https://orcid.org/0009-0000-6911-0708
  • Mykhailo Lopatetskyi National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, Ukraine

DOI:

https://doi.org/10.20535/tacs.2664-29132025.2.339994

Abstract

This paper considers the problem of estimating the security of the lightweight block cipher LBlock against differential cryptanalysis. We formalize the process and present two algorithms of computing upper bounds for differential probabilities. The baseline algorithm provides approximate estimates based on the number of active S-boxes, while the refined algorithm incorporates the full probability distributions of S-box differentials, yielding significantly better bounds.

To illustrate the efficiency of the proposed methodology, we introduce a modified version of LBlock with 8x8 S-boxes, which has lower computational complexity and allows experimental evaluation on our resources.We consider different linear permutations of encryption round, analyzing affect the estimates produced by both algorithms.The results demonstrate that the refined algorithm achieves much smaller maximum bounds (below 2-40 in the best cases) compared to the baseline approach and provides a more accurate characterization of security against differential cryptanalysis.

Overall, the proposed algorithms make it possible to efficiently evaluate the provable security of LBlock-like ciphers
against differential cryptanalysis.

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Published

2025-11-17

Issue

Vol. 7 No. 2 (2025): Theoretical and Applied Cybersecurity

Section

Theoretical and cryptographic problems of cybersecurity

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