Efficient and Secure Image Encryption using Key Substitution Process with Discrete Wavelet Transform

The protection of digital images has become increasingly important with the rapid growth of multimedia communication over open networks. Conventional encryption techniques, which were originally designed for textual data, often face limitations when applied directly to image data due to its large size, high redundancy, and strong pixel correlation. To address these challenges, this study presents a hybrid image security framework that integrates encryption and steganography for secure image transmission. In the proposed approach, the secret image is first processed using a multi-level Discrete Wavelet Transform (DWT) to obtain wavelet coefficients. These coefficients are then scaled and subjected to a dynamic key-dependent substitution mechanism generated through a cryptographic hash-based S-Box. A chaotic logistic map is further employed to perform permutation and diffusion operations, thereby increasing randomness and enhancing resistance to cryptographic attacks. After encryption, the cipher data is embedded into a cover image using a two-least significant bit (2-LSB) steganography technique to conceal the presence of the encrypted information. Experimental evaluation using metrics such as PSNR, SSIM, NPCR, UACI, entropy, and correlation demonstrates strong security performance and effective resistance against statistical and differential attacks. The results suggest that the proposed method provides a reliable and efficient approach for secure image protection in modern communication environments.