Finely Tunable Bitcuboid-Based Encryption With Exception-Free Signed Binarization for JPEG Standard

We propose a finely tunable JPEG format-compliant perceptual encryption (FE) with two novel strategies: (i) bitcuboid-based encryption (BE) and (ii) exception-free signed binarization (ESB). BE is an intra- and inter-bitplane encryption technique that provides finely tunable perceptual degradation by encrypting constrained subspaces (‘bitcubes’) of a cuboid-shaped bit set (‘bitcuboid’). ESB is a binarization technique that redecimalizes encrypted binary sequences into signed decimal coefficients without any exception-handling by shifting the negative binary sequences one-by-one. BE with ESB (BEESB) is applied to the quantized discrete cosine transform (QDCT) domain in JPEG compression. The results of our first experiment show that the BE attains fine tunability, which means scalability of the perceptual degradation level with a single encryption method, by encrypting bitcubes of various types and sizes combinatorially. The results of our second experiment show that the BEESB suppresses the bitrate overheads and that BEESB with one of the most secure options suppresses approximately 0.80-187.58 % more of the bitrate overheads in terms of Bjøntegaard delta (BD)-rate compared with conventional methods except for some ones. The results of our third experiment show that BEESB has high resilience against attacks.