Joint JPEG Compression and Encryption Scheme Based on Order-8-16 Block Transform

Joint image compression and encryption techniques can be used to ensure the security of JPEG images. The related works in this field face problems such as low compression efficiency, limited protection power, and corrupted format information. In this paper, we propose a new JPEG protection method by introducing encryption operations into the compression process. Considering that different images have different properties, instead of using a fixed block size for encryption, we develop a new block segmentation strategy to first divide the plain-image into two different sizes of blocks,
$8\times 8$
and
$16\times 16$
, followed by corresponding size of DCT’s transformation. The strategy can ensure that the file size increment and rate-distortion are minimal. After block transformation and quantization, we encrypt DC coefficients by XOR and swapping, while AC coefficients are protected through block permutation and data embedding. The experiments show that our scheme does not compromise JPEG’s compression efficiency, offers satisfied security and maintains the format-compliant of the final encrypted bitstream to JPEG’s decoder.