| Resumen |
JPEG encryption with the Encrypion-Then-Compression (EtC) scheme allows for encrypted images to be still considered as images and not only as encrypted data. This makes them compatible with social media and cloud platform requirements. On the other hand, substitution boxes are a traditional encryption tool in modern image cryptosystems because of their benefits to enhance security. However, EtC does not include them for keeping image format compatibility. This argument is only mentioned and not explained in regular papers. Therefore, the purpose of this paper is to explore the results that lead to this incompatibility. Although a plain image has differences in the pixel values after JPEG lossy compression, they are not perceived by the human visual system. However, the substitution boxes generate superior pixel-value differences that are perceptible. This paper shows the aforementioned using the AES S-Box. The numerical change effect in pixels from substitution to lossy compression execution is analyzed. The simulations show that the procedure falls on the fact that the decrypted JPEG image is not a sufficient approximation to recognize the original. Finally, the differences between the encrypted and plain images to support JPEG lossy compression are reported. © 2023 IEEE. |
