Abstract
Invariant Commutative Watermarking-Encryption means to use a cipher that does not have any impact on a certain feature space, which can thus be used for embedding watermarks either before or after encryption. For example, histogram-based watermarking schemes are invariant to pixel permutations and can be combined with permutation-based ciphers to form a Commutative Watermarking-Encryption (CWE) scheme. However, typical histogram-based watermarking schemes based on comparison of histogram bins are prone to de-synchronization attacks, where the whole histogram is shifted by a certain amount. In this paper the authors investigate the possibility to avoid this kind of attacks by synchronizing the embedding and detection processes, using the mean of the histogram as a calibration point. The resulting watermarking scheme is resistant to three common types of shifts of the histogram, while the advantages of previous histogram-based schemes, especially commutativity of watermarking and permutation-based encryption, are preserved. The authors also report on the results of testing robustness of the scheme against JPEG and JPEG2000 compression.