Hybrid Vigenère-Hill Approach for Color Image Encryption

Abstract

This paper introduces an enhanced encryption scheme for color images, combining improved Vigen re and Hill cipher techniques.Our approach leverages two carefully selected chaotic maps, exploiting their extreme sensitivity to initial conditions for cryptographic security.The encryption process begins with RGB channel separation and vector conversion, followed by initial confusion operations generating a partially encrypted image vector.This vector is then divided into 3-pixel subblocks for subsequent processing.Each block undergoes multi-stage encryption controlled by a binary vector, employing three expanded substitution tables with optimized confusion-diffusion functions.These functions operate sequentially across pixels with chaining mechanisms between adjacent pixels.The modified Hill cipher then processes each block using an invertible matrix combined with dynamic translation vectors, effectively addressing the linearity limitations of traditional Hill cipher implementations.To enhance security, we implement an inter-block diffusion mechanism that dynamically links each block's final encrypted pixel with the next block's initial pixel through a specialized diffusion function.This design significantly strengthens avalanche effects while providing robust resistance against differential attacks.Tests on a diverse set of randomly chosen color images yielded statistical (histogram, correlation, entropy) and differential (UACI, NPCR) metrics meeting international standards, confirming our cryptosystem's robustness against known attacks.