A new design of multiple transforms for perceptual video encryption

Perceptual (or partial) video encryption has recently been achieved via a random-key controlled selection among multiple transforms, where these transforms are designed by modifying the rotation angles at the last stage of the DCT's butterfly structure. Later on, it was found that more efficient transforms can be obtained by applying random sign-flips at the same stage, which is equivalent to an extra rotation angle of 180°. In this paper, we generalize this technique by embedding random sign-flips into other stages in the DCT's implementation structure. To this end, we first convert the separable implementation of the H.264 4×4 2-D DCT into a 1-D 16-point structure so that more sign-flips can be embedded at its various stages. Then, we introduce different pairing schemes (i.e., forming N/2 pairs for a group of N node-variables) to further increase the encryption space. Extensive experiments are carried out to show the performance of this improved video encryption scheme; whereas security analyses are conducted to show the newly designed transforms out-perform the previous ones in terms of search space and encryption efficiency.