On the security of JPEG image encryption with RS pairs permutation

Abstract

Recently, a JPEG encryption scheme with RS (run/size) pairs multi-permutation and block permutation has been proposed, which mainly improves security by extracting the expected number of RS pairs for global permutations that need overflow processing. However, it still has the risk of information leakage under the chosen plaintext attack. This is because the limited embedding capacity in overflow processing makes the overflow blocks (OBs) less. On the one hand, a few OBs make the sketch generated by non-zero coefficients count after RS pair multi-permutation visually indistinguishable from the original sketch. On the other hand, a few OBs limit the number of extracted RS pairs that can participate in global permutation, so there are many partially extracted blocks (PEBs) containing unextracted RS pairs. More PEBs make the accuracy of the estimated block permutation sequence high, because the unique plaintext block can be constructed as long as there is an unextracted RS pair in an encrypted block. Simulation results show that the correct ratio of block permutation sequence is not less than 60 %. The highest and average PSNRs between the attacked sketch and the original one reach up to 47.07 dB and 27.42 dB, respectively.