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<p>The two basic prerequisites for encryption techniques based on block ciphers are confusion and diffusion. Substitution boxes( S-boxes) are used in contemporary block ciphers to create ciphertext by randomly disrupting the plaintext underneath. The resilience and security of a block cipher are strongly reliant on the quality of its S-box, which provides the essential nonlinearity and complexity to deter potential attackers. We introduced a new technique in this study that generates cryptographically resilient S-boxes by applying fractional transformation on a finite field. Firstly, we introduced some bijective power functions on the Galois field of order 256. Later, we introduced a new function named Extended fractional transformation (EFT) using the composition of Linear fractional transformation (LFT) and power functions. It includes a comprehensive assessment of the basic performance of the designated S-box using benchmarking criteria. Achieving low differential uniformity, measuring strong nonlinearity, satisfying SAC and BIC features, and evaluating the linear approximation probability are all part of these requirements. Furthermore, a developed S-box is used in a proposed medical image encryption method to effectively perform pixel substitution and shuffling. We conducted a number of tests to assess the proposed scheme’s strength. In terms of application, the proposed S-box outperforms S-boxes created using the LFT technique in terms of cryptographic strength without the need for additional permutations.</p>

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Extended fractional transformation based S-box and applications in medical image encryption

  • 期刊论文

  • 发表日期：

    2025年1月4日

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  • Javed Ali,
  • Muhammad Kamran Jamil,
  • Rashad Ali,
  • Gulraiz

摘要

The two basic prerequisites for encryption techniques based on block ciphers are confusion and diffusion. Substitution boxes( S-boxes) are used in contemporary block ciphers to create ciphertext by randomly disrupting the plaintext underneath. The resilience and security of a block cipher are strongly reliant on the quality of its S-box, which provides the essential nonlinearity and complexity to deter potential attackers. We introduced a new technique in this study that generates cryptographically resilient S-boxes by applying fractional transformation on a finite field. Firstly, we introduced some bijective power functions on the Galois field of order 256. Later, we introduced a new function named Extended fractional transformation (EFT) using the composition of Linear fractional transformation (LFT) and power functions. It includes a comprehensive assessment of the basic performance of the designated S-box using benchmarking criteria. Achieving low differential uniformity, measuring strong nonlinearity, satisfying SAC and BIC features, and evaluating the linear approximation probability are all part of these requirements. Furthermore, a developed S-box is used in a proposed medical image encryption method to effectively perform pixel substitution and shuffling. We conducted a number of tests to assess the proposed scheme’s strength. In terms of application, the proposed S-box outperforms S-boxes created using the LFT technique in terms of cryptographic strength without the need for additional permutations.