基于中文标点的隐写术设计与实现

隐写术是一种保障信息安全的重要方法。在普通文本中隐藏信息,因其包含的信息冗余量少而难以实现。提出了一种基于中文标点信息隐藏的新方法,利用标点具有全角和半角之分的特点,在文本中使用标点互换来隐藏秘密,方法简单实用、可操作性强,通过实验证明能达到信息伪装的目的。     

A high capacity reversible data hiding scheme with edge prediction and difference expansion

To enhance the embedding capacity of a reversible data hiding system, in this paper, a novel multiple-base lossless scheme based on JPEG-LS pixel value prediction and reversible difference expansion will be presented. The proposed scheme employs a pixel value prediction mechanism to decrease the distortion caused by the hiding of the secret data. In general, the prediction error value tends to be much smaller in smooth areas than in edge areas, and more secret data embedded in smooth areas still meets better stego-image quality. The multiple-base notational system, on the other hand, is applied to increase the payload of the image. With the system, the payload of each pixel, determined by the complexity of its neighboring pixels, can be very different. In addition, the cover image processed by the proposed scheme can be fully recovered without any distortion. Experimental results, as shown in this paper, have demonstrated that the proposed method is capable of hiding more secret data while keeping the stego-image quality degradation imperceptible.     

Post-retrieval search hit clustering to improve information retrieval effectiveness: Two digital forensics case studies

This research extends text mining and information retrieval research to the digital forensic text string search process. Specifically, we used a self-organizing neural network (a Kohonen Self-Organizing Map) to conceptually cluster search hits retrieved during a real-world digital forensic investigation. We measured information retrieval effectiveness (e.g., precision, recall, and overhead) of the new approach and compared them against the current approach. The empirical results indicate that the clustering process significantly reduces information retrieval overhead of the digital forensic text string search process, which is currently a very burdensome endeavor.     

Fast two-layer image watermarking without referring to the original image and watermark

A fast two-layer image watermarking without referring to the original image and watermark is proposed in this study. Two layers of algorithms are employed to simultaneously hide the same watermarks in the spatial domain. More specifically, the first layer watermarking resists high-frequency destruction, while that in layer two resists low-frequency destruction. Although the image is modified through two layers of watermarking, the watermarks are still invisible. In addition, the proposed watermarking has other advantages. First, the proposed embedding technique is based on an intra-relationship within the original image rather than an inter-relationship between the original and watermarked images so that the original image is not required during the detection process. Second, the proposed watermark is composed of fixed and variable parts. The fixed part allows the detection of the watermark existence and location without referring to the original watermark. The variable part permits greater flexibility and variety of watermarks. Third, the proposed watermark is a short serial number, which allows it to be duplicated. Because of the duplication, a majority voting strategy can be employed to facilitate watermark detection. Finally, the proposed method is fast and simple. It takes only one or two seconds for either the embedding stage or the detection stage. Various experiments have been conducted to verify the above advantages of the two layer watermarking.     

On optimal policies for control and estimation over a Gaussian relay channel

The problem of causal transmission of a memoryless Gaussian source over a two-hop memoryless Gaussian relay channel is considered. The source and the relay encoders have average transmit power constraints, and the performance criterion is mean-squared distortion. The main contribution of this paper is to show that unlike the case of a point-to-point scalar Gaussian channel, linear encoding schemes are not optimal over a two-hop relay channel in general, extending the sub-optimality results which are known for more than three hops. In some cases, simple three-level quantization policies employed at the source and at the relay can outperform the best linear policies. Further a lower bound on the distortion is derived and it is shown that the distortion bounds derived using cut-set arguments are not tight in general for sensor networks.     

Analysis of the “Wavelet Tree Quantization” watermarking strategy and a modified robust scheme

Here we study a recently proposed watermarking scheme based on the paper “Wavelet Tree Quantization” (WTQ) by Wang and Lin (IEEE Trans Image Process 13(2):154–165, 2004). In given scheme, wavelet coefficients corresponding to the same spatial locations are grouped together. Two such groups, selected at random, constitute a supertree. Some of these supertrees are quantized to embed the watermark information in the image. In the process of cryptanalysis we first identify the groups which are quantized during the watermark insertion process. Then we select the non-quantized groups and quantize them too, to remove the watermark. Experimental results show that the watermark is completely removed by this attack. The cryptanalysis falls under the cipher text only jamming attack which requires only a single watermarked copy. Further, we suitably modify the WTQ scheme to make it robust against such cryptanalytic attacks.This is an extended and revised version of the paper Cryptanalysis of “Wavelet Tree Quantization” Watermarking Scheme presented at the International Workshop on Distributed Computing, IWDC 2004, Kolkata, 27–30 December 2004, Lecture Notes in Computer Science, vol. 3326, pp. 219–230. Springer, Berlin Heidelberg New York (2004). Section 4 of this paper introduces a modified scheme which is an addition over the conference version. Part of this work has been done while the author T. K. Das was visiting Indian Statistical Institute, Kolkata during 2004.