Substitution boxes (S-box) with strong and secure cryptographic properties are widely used for providing the key property of nonlinearity in block ciphers. This is critical to be resistant to a standard attack including linear and differential cryptanalysis. The ability to create a cryptographically strong S-box depends on its construction technique. This work aims to design and develop a cryptographically strong 8 × 8 S-box for block ciphers. In this work, the construction of the S-box is based on the linear fractional transformation and permutation function. Three steps involved in producing the S-box. In step one, an irreducible polynomial of degree eight is chosen, and all roots of the primitive irreducible polynomial are calculated. In step two, algebraic properties of linear fractional transformation are applied in Galois Field GF (2⁸). Finally, the produced matrix is permuted to add randomness to the S-box. The strength of the S-box is measured by calculating its potency to create confusion. To analyze the security properties of the S-box, some well-known and commonly used algebraic attacks are used. The proposed S-box is analyzed by nonlinearity test, algebraic degree, differential uniformity, and strict avalanche criterion which are the avalanche effect test, completeness test, and strong S-box test. S-box analysis is done before and after the application of the permutation function and the analysis result shows that the S-box with permutation function has reached the optimal properties as a secure S-box.

As quantum computing advances, classical public-key cryptosystems face escalating risks, driving global standardization efforts by NIST, ETSI, and ISO. This paper provides a comprehensive review of recent developments in post-quantum cryptography (PQC), focusing on lattice-based, hash-based, and multivariate approaches. We examine their security foundations, implementation challenges, and applicability across domains such as finance, blockchain, and the Internet of Things (IoT). A core contribution is the proposed Hybrid Cryptographic Framework (HCF), which combines classical and quantum-resistant primitives to enable a secure and interoperable migration path. The framework integrates hybrid key exchange, dual-signature schemes, and PQC-compatible Merkle trees, and is supported by a discrete multi-objective optimization model for selecting algorithms under real-world constraints. The paper also discusses deployment challenges, including hardware acceleration, side-channel resistance, and legacy compatibility. Real-world case studies illustrate how leading institutions are piloting PQC integration in practice. Finally, we propose a strategic roadmap for PQC adoption, incorporating adaptive triggers based on quantum capabilities and evolving threat models. By aligning cryptographic design with international standards and practical system requirements, this work offers guidance for building resilient, quantum-safe infrastructures.

A New Digital Signature Scheme Based on Factoring and Discrete Logarithms