Flexibly-Tunable Bitcube-Based Perceptual Encryption Within Jpeg Compression

We propose a perceptual encryption within JPEG compression (EWJ). Although some of the conventional EWJs have the `tunability,' which is a property of how many perceptual degradation levels can be provided with the single encryption technique, it is insufficient because either strong level of security or low bitrate overhead is regarded as important. The proposed EWJ detects the specific subspaces of the bits in the quantized discrete cosine transform (QDCT) coefficient blocks (`bitcubes'), such that the non-zero bits crowd, and then the bits are permuted within each bitcube, i.e., not only within each bitplane like the conventional EWJs but also between adjacent bitplanes. The experiments show the bitcube-based EWJ actually provides more flexible tunability than the conventional EWJs, while compromising the relation between the bitrate overhead and the attack robustness.