SPJEU: a self-sufficient plaintext-related JPEG image encryption scheme based on a unified key

Abstract

In recent research on image encryption, many schemes associate the key generation mechanism with the plaintext to resist chosen plaintext attacks. However, when the sender encrypts many images, a large amount of additional data related to the plaintext need to be transmitted, which leads to problems such as high transmission costs, high requirements for key storage space, and complex key management. Therefore, in this paper, we propose a self-sufficient plaintext-related JPEG image encryption scheme based on a unified key (SPJEU). This scheme establishes the connection between the plaintext and the key by selecting the direct current (DC) coefficients in the JPEG image through a unified key. Homomorphic encryption is applied to the selected DC coefficients, allowing plaintext information to be decrypted directly from the ciphertext domain using a specific calculation method. The remaining DC coefficients are encrypted through group diffusion, and the alternating current (AC) coefficients are grouped and permuted based on the run length. Extensive experiments show that our scheme can resist chosen plaintext attacks, avoid transmitting plaintext-related additional data in the communication channel, and simplify key management. This scheme also ensures the security and format compatibility of the ciphertext image, and the file increment after encryption is very small.

1. Introduction

Digital images are important multimedia resources on the Internet, and many are posted on network platforms every day. For convenience, users store or share a large amount of online image data to the cloud. To prevent privacy leakage, the most common solution is image encryption (Li M et al., 2022). However, traditional encryption methods such as advanced encryption standard (AES) and data encryption standard (DES) are not suitable for image encryption because the data contained in the image are redundant and correlated (Liu et al., 2016).

Effective image encryption can be performed in either the spatial domain or the frequency domain. Spatial domain encryption involves encrypting the pixels of the image directly. Frequency domain encryption means that the image is transformed from the spatial domain to the frequency domain using transforms such as Fourier, discrete cosine, or wavelet, and the coefficients in the frequency domain are encrypted (Refregier and Javidi, 1995).

The main techniques used in both spatial image encryption and frequency image encryption are scrambling and diffusion (Zheng et al., 2017; Yi et al., 2018; Mohammadi et al., 2020; Xian et al., 2022). For example, Yi et al. (2018) and Mohammadi et al. (2020) used a stream cipher to encrypt images by block-based scrambling and pixel-XOR diffusion. Zheng et al. (2017) combined DNA encoding with an XOR operation. Xian et al. (2022) used the spiral-transform-based fractal sorting matrix (STFSM) chaotic system to scramble and diffuse images. At present, the most commonly used image format on the Internet is JPEG, so it is meaningful to encrypt JPEG images (Li WH and Yuan, 2007).