A Hybrid AES–NTRU Cryptographic Framework with Deterministic Dynamic S-Box for Secure Data Transmission

Abstract

The rapid expansion of interconnected sensing and monitoring systems has significantly increased the volume of digital data exchanged across distributed environments. While these systems provide substantial benefits for real-time monitoring and automated decision making, they also introduce critical challenges related to data confidentiality and secure communication. This study proposes a hybrid cryptographic framework designed to strengthen secure data transmission in distributed sensing environments. The primary objective of this research is to integrate a symmetric encryption mechanism with a lattice-based public-key cryptographic scheme within a hybrid key protection architecture. In addition, a deterministic round-dependent substitution mechanism is introduced into the symmetric encryption process to provide controlled structural variability during data encryption while preserving compatibility with the standard round-based encryption structure. The proposed framework was implemented in a software-based prototype environment and evaluated through a series of encryption and decryption experiments using representative data payloads that emulate typical communication scenarios in distributed sensing systems. The evaluation focused on three aspects: implementation correctness, computational performance, and diffusion characteristics of the encryption process. Experimental results confirm that all encrypted data payloads were successfully decrypted to their original plaintext without bit errors, demonstrating the functional correctness of the integrated cryptographic architecture. The encryption process achieved an avalanche effect of 47.01 percent, with an average encryption time of 118.99 milliseconds and a decryption time of 5.91 milliseconds in the prototype environment. These results indicate consistent diffusion behavior within acceptable experimental bounds while maintaining reasonable computational overhead for gateway-level communication nodes. The findings suggest that integrating adaptive substitution mechanisms within hybrid cryptographic architectures can provide flexible encryption structures suitable for secure data transmission in distributed monitoring systems, while remaining compatible with widely deployed symmetric encryption frameworks.