Trends in Increasing the Crypto-Strength of Symmetric Block Civers in the Context of the Modern Cryptosystems Development

<ns0:p>The article examines the combination of analytical and applied approaches to improving symmetric block ciphers in light of current trends in the development of cryptographic systems. The study analyzes the current SOG-IS standards and recommendations that define the basic directions of symmetric algorithm evolution, such as the transition from outdated Feistel-based schemes to optimized structures (AES, lightweight block ciphers for IoT). Using a modified version of the Simple-DES (S-DES) cipher, the paper proposes a method for enhancing cryptographic strength without changing the key or block length. The main improvements involve an enhanced design of S-boxes and their dynamic selection based on a key graph. The results of the comparative analysis demonstrate a significant increase in resistance to brute-force and differential cryptanalysis compared to the standard S-DES, while maintaining low computational complexity. The conducted research confirms the relevance of using educational and experimental models such as S-DES to explore modern methods for improving the security of symmetric ciphers, which is of practical importance for prototyping and lightweight implementations in Internet of Things systems.</ns0:p>