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.