Xingbin Liu

Efficiency and security issues are significant considerations in the transmission of information. The joint compression and encryption method is an effective way to improve both issues. In this paper, a novel chaos system named logistic coupled sine and exponential function map (LSEM) and a joint JPEG compression and encryption scheme are proposed. Unlike existing JPEG image schemes, a scanning permutation before the differential pulse code modulation (DPCM) is proposed, containing two scanning modes, which can achieve good scrambling performance while reserving file space for subsequent encryption. In addition, an inter-group cross-permutation on random groups of DC coefficients is designed to permute the DC coefficients. The DC coefficients are grouped according to random length and position, and subsequently subjected to inter-group cross-permutation based on random indexes generated with the proposed chaotic system. For AC coefficients, an inter-block permutation method is proposed to change ZRV (zero-run length, value of a non-zero quantized AC coefficient) pairs quantities, which can effectively alter the corresponding block features and the histogram distribution. Experimental results demonstrate that the proposed scheme is reliable in protecting JPEG images while suppressing file size growth and maintaining format compatibility. Notably, the scanning permutation can reserve an average of 0.055% and 0.162% file size for the test images under scanning modes 1 and 2, respectively. The NPCR and UACI results for sensitivity analysis are close to the ideal values. Besides, the change rate of block features is no less than 90% under different quality factors.