An Optimized Cascaded Cryptosystem Using AES-256 and SPECK-128

Abstract

With the rapid proliferation of high-resolution digital media across untrusted networks, ensuring visual data confidentiality and integrity requires robust, high-throughput cryptographic architectures. Standard block ciphers applied directly to high-dimensional image payloads often introduce computational latency, spatial redundancy vulnerabilities, or bottleneck challenges when paired with legacy ciphers. This paper presents a performance and cryptographic evaluation of an optimized cascaded dual-stage image cryptosystem combining a 14-round Advanced Encryption Standard primary layer (AES-256 in Counter mode) with a secondary 32-round SPECK-128/128 lightweight block cipher stage. Plaintext images are flattened into contiguous linear byte arrays for dual-stage cipher transformations before undergoing exact 3D spatial tensor reconstruction (). We evaluate the implementation using rigorous statistical and differential security metrics—including Shannon entropy, adjacent pixel correlation analysis, Number of Pixels Change Rate (NPCR), and Unified Average Changing Intensity (UACI). Experimental results demonstrate that the AES-256 + SPECK-128 framework achieves near-ideal information entropy (), drastically reduces adjacent pixel correlation from  to , and satisfies theoretical differential attack resistance baselines (, ). Furthermore, replacing legacy secondary ciphers with SPECK-128 significantly reduces execution latency, confirming the system's suitability for real-time, low-latency secure image transmission.