A hybrid encryption algorithm based on AES and Kyber for secure image protection in the post-quantum era

Abstract

The exponential rise in the sharing of multimedia information is accompanied by an increase in vulnerability during data exchange. As quantum computing is threatening the fundamentals of classical cryptography, it is important that multimedia data be protected by quantum-secured encryption techniques. Hybrid encryption that combines symmetric cyphers with post-quantum key encapsulation is an established architectural pattern, but its use for image data has not been explored in depth. This paper presents Quantum Good Privacy (QGP), a hybrid image-encryption scheme that combines AES-256 in Cipher Block Chaining (CBC) mode with the Module-Lattice-based Key Encapsulation Mechanism (ML-KEM, originally Kyber) and evaluates this architecture on image data through statistical and timing tests. QGP-CBC achieves entropy consistently above 7.996 (mean: 7.9963), approaching the ideal 8 bits/pixel, a low Peak Signal-to-Noise Ratio (8.24 dB), a strong Number of Pixel Change Rate (99.62%), and a Unified Average Changing Intensity (31.67%) value, providing strong confusion and diffusion properties. It is an efficient method as it requires 2.1 ms for encrypting and 0.79 ms for decrypting 256 × 256 image data, respectively, while encapsulation and decapsulation of keys take only 0.068 ms and 0.051 ms, respectively. QGP-CBC passes the NIST SP800-22 randomness test, thus making it suitable for use in secure image transmission in the post-quantum world. QGP-CBC and QGP-ECB have similar Number of Pixel Change Rate and Unified Average Changing Intensity values, but QGP-CBC passes all 16 NIST SP800-22 randomness tests while QGP-ECB fails four, making it the more statistically robust choice for image encryption.