Security and synchronization in watermark sequence

In a mature watermarking and steganography application, the security should lie in the unknown random keys not in the embedding algorithms. In this paper, the problem of the selection of watermarking random sequences is investigated. In the widely used Spread Spectrum modulation schemes, a white sequence and a Low-Pass (LP) type sequences are analyzed, including its security level and synchronization requirements. It is found that the white independent is more secure but not robust against LP attack. Also it is not energy efficient. Actually The random sequence selection is usually the tradeoff between these factors. To be resilient to the removal attacks, the watermark spectrum should be similar to the spectrum of the cover signal. A watermarking sequence with fixed amplitude spectrum shape and random phase is proposed in the last part of the paper and its properties are discussed in detail.