Z-Crypt: Chirp Z-Transform-Based Image Encryption Leveraging Chaotic Logistic Maps and Substitution Permutation Network

In the current era of digital communication, image security is a top priority as sending images, which often contain personal or confidential information, over the Internet poses security risks. Many encryption algorithms have been proposed in the literature to address this issue. However, these algorithms have limitations, such as low-key space, high computational overhead, and susceptibility to differential attacks. To address these limitations, this paper proposes Z-Crypt, a novel image encryption approach that combines a substitution-permutation network (SPN) and a chaotic logistic map (CLM) with the Chirp Z-Transform (CZT) to enhance security and resist attacks. The CLM-generated matrices introduce confusion and diffusion, while SPN creates a dissociation of the cipher from the plaintext. Finally, the CZT strengthens the encryption by transforming the image into the frequency domain, creating multiple layers of confusion and diffusion to produce a robust encryption algorithm. We have evaluated the proposed Z-Crypt's security using various metrics, including correlation coefficient, entropy, peak signal-to-noise ratio (PSNR), and key sensitivity analysis. Experimental results verify that the proposed algorithm outperforms existing methods, achieving high security while maintaining computational efficiency.