Transparent and perceptually enhanced JPEG image encryption

In many applications encryption/decryption of compressed images or videos is desired to be transparent to the compression decoder to maintain the file format, file size and content-relevant functionalities. We propose in this paper a transparent encryption mechanism for JPEG-encoded image files to meet the requirements of format-compliance and file-size preservation. The algorithm is based on a special cross-block varied-length codes (VLC) shuffling method perceptually enhanced by a reversible histogram spreading processing, which tends to smoothly re-distribute VLCs among spatial blocks in a reversible way. The algorithm performs visually better than existing shuffling based schemes against content leakage attacks such as DC value removal.