Abstract
Focusing on the encryption of digital image and video, an intrinsic weakness of all existing discrete-cosine-transform (DCT) based algorithms is reported. This serious weakness of DCT-based encryptions is analysed theoretically and then demonstrated practically. As an instance, a novel attack algorithm is proposed to acquire the sketch information from encrypted data without any prior knowledge of the encryption algorithm. The quality of the extracted sketch is then evaluated by comparing with the original picture edge. Thereafter, to prevent this kind of attack, a full inter-block shuffle (FIBS) approach is proposed. This method can be employed to improve the encryption security in all DCT-based algorithms, such as JPEG, MPEG video and H.26x video.
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