A New 12-Bit Chaotic Image Encryption Scheme Using a 12 × 12 Dynamic S-Box

The use of 12-bit levels of grayscale in medical image representation allows for more precise image analysis and diagnosis, and encrypting such images is essential for protecting patient privacy and security. Existing 8-bit image encryption schemes become inefficient when applied to 12-bit images. In this paper, we design a cryptographically strong encryption scheme to improve the efficiency of encrypting 12-bit medical images. The core of the proposed scheme is a key-dependent
$12\times 12$
S-box, which plays a crucial role in enhancing the security and efficiency of the encryption scheme. Most notably, test results show that
$12\times 12$
S-boxes offer significantly stronger confusion and key-sensitivity than their
$8\times 8$
counterparts. This finding enables the proposed
$12\times 12$
S-box-based scheme to process 12-bit images 3.3 times faster than an
$8\times 8$
S-box while passing all security tests. Experimental results show that the proposed scheme can encrypt 12-bit images at speeds up to 300MB/s. Moreover, the proposed scheme has also been shown to efficiently handle 8-bit images. Comparative results highlight the security and efficiency advantages of the proposed scheme over existing medical image encryption schemes.