Chwei-Shyong Tsai

A high quality steganographic method with pixel-value differencing and modulus function

In this paper, we shall propose a new image steganographic technique capable of producing a secret-embedded image that is totally indistinguishable from the original image by the human eye. In addition, our new method avoids the falling-off-boundary problem by using pixel-value differencing and the modulus function. First, we derive a difference value from two consecutive pixels by utilizing the pixel-value differencing technique (PVD). The hiding capacity of the two consecutive pixels depends on the difference value. In other words, the smoother area is, the less secret data can be hidden; on the contrary, the more edges an area has, the more secret data can be embedded. This way, the stego-image quality degradation is more imperceptible to the human eye. Second, the remainder of the two consecutive pixels can be computed by using the modulus operation, and then secret data can be embedded into the two pixels by modifying their remainder. In our scheme, there is an optimal approach to alter the remainder so as to greatly reduce the image distortion caused by the hiding of the secret data. The values of the two consecutive pixels are scarcely changed after the embedding of the secret message by the proposed optimal alteration algorithm. Experimental results have also demonstrated that the proposed scheme is secure against the RS detection attack.

Reversible Watermarking: Current Status and Key Issues

Over the past few years a number of research papers about reversible watermarks has been produced. Reversible watermarking is a novel category of watermarking schemes. It not only can strengthen the ownership of the original media but also can completely recover the original media from the watermarked media. This feature is suitable for some important media, such as medical and military images, because these kinds of media do not allow any losses. The aim of this paper is to define the purpose of reversible watermarking, reflecting recent progress, and provide some research issues for the future.

Password Authentication Schemes: Current Status and Key Issues

Password authentication is one of the simplest and the most convenient authentication mechanisms to deal with secret data over insecure networks. It is more frequently required in areas such as computer networks, wireless networks, remote login systems, operation systems, and database management systems. In this paper, we shall present the result of our survey through all currently available password-authentication-related schemes and get them classified in terms of several crucial criteria. To be critical, most of the existing schemes are vulnerable to various attacks and fail to serve all the purposes an ideal password authentication scheme should. In order to see how different password authentication schemes compare in different situations, we define all possible attacks and goals that an ideal password authentication scheme should withstand and achieve. We should hope that the attacks and goals we offer here can also help future researchers develop better schemes.

Adaptive lossless steganographic scheme with centralized difference expansion

In this paper, a novel adaptive lossless data hiding scheme is presented that is capable of offering greater embedding capacity than the existing schemes. Unlike the fixed hiding capacity each block provides in most of the currently available lossless data hiding approaches, the proposed method utilizes a block-based lossless data embedding algorithm where the quantity of the hidden information each block bears is variable. To both reduce the image distortion and increase the hiding capacity, the payload of each block depends on its cover image complexity. Due to the fact that schemes with difference expansion tend to damage the image quality seriously in the edge areas, in the proposed scheme, smoother areas are chosen to conceal more secret bits. This way, a better balance can be reached between the embedding ratio and the stego-image quality. In addition, when recovered the cover image can came back to its old self to the last bit without any distortion at all. Experimental results, as this paper will show, have demonstrated that the proposed method is capable of hiding more secret data while maintaining imperceptible stego-image quality degradation.

A new multi-secret images sharing scheme using Largrange's interpolation

Secret sharing is to send shares of a secret to several participants, and the hidden secret can be decrypted only by gathering the distributed shares. This paper proposes an efficient secret sharing scheme using Largranges interpolation for generalized access structures. Furthermore, the generated shared data for each qualified set is 1/(r-1) smaller than the original secret image if the corresponding qualified set has r participants. In our sharing process, a sharing circle is constructed first and the shared data is generated from the secret images according to this sharing circle. The properties of the sharing circle not only reduce the size of generated data between two qualified sets but also maintain the security. Thus the actual ratio of the shared data to the original secret images is reduced further. The proposed scheme offers a more efficient and effective way to share multiple secrets.

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.

A HDWT-based reversible data hiding method

This paper presents a reversible data hiding method which provides a high payload and a high stego-image quality. The proposed method transforms a spatial domain cover image into a frequency domain image using the Haar digital wavelet transform (HDWT) method, compresses the coefficients of the high frequency band by the Huffman (or arithmetic) coding method, and then embeds the compression data and the secret data in the high frequency band. Since the high frequency band incorporates less energy than other bands of an image, it can be exploited to carry secret data. Furthermore, the proposed method utilizes the Huffman (or arithmetic) coding method to recover the cover image without any distortion. The proposed method is simple and the experimental results show that the designed method can give a high hiding capacity with a high quality of stego-image.

Generalization of proxy signature based on elliptic curves

Abstract In the past, proxy signature schemes were usually proposed to deal with one or two separate proxy conditions each. To make a difference, in this paper, the authors shall present a generalized version of proxy signature scheme. Compared to earlier proxy signature schemes, our novel scheme can be applied to every possible proxy situation. The proposed scheme allows the original group of original signers to delegate their signing capability to a designated proxy group. The proxy group of proxy signers can cooperatively generate a proxy signature on behalf of the original group. Any verifier can verify the proxy signature on the message with the knowledge of the identities of the actual original signers and the actual proxy signers. With this article, we also aim to demonstrate how to specify proxy signature schemes on elliptic curve over finite fields. In addition, some possible attacks have also been considered, and our security analysis will show that none of them can successfully break the proposed scheme.

A novel adaptive steganography based on local complexity and human vision sensitivity

This paper presents a novel adaptive steganographic scheme that is capable of both preventing visual degradation and providing a large embedding capacity. The embedding capacity of each pixel is dynamically determined by the local complexity of the cover image, allowing us to maintain good visual quality as well as embedding a large amount of secret messages. We classify pixels into three levels based on the variance of the local complexity of the cover image. When determining which level of local complexity a pixel should belong to, we take human vision sensitivity into consideration. This ensures that the visual artifacts appeared in the stego image are imperceptible, and the difference between the original and stego image is indistinguishable by the human visual system. The pixel classification assures that the embedding capacity offered by a cover image is bounded by the embedding capacity imposed on three levels that are distinguished by two boundary thresholds values. This allows us to derive a combination ratio of the maximal embedding capacity encountered with at each level. Consequently, our scheme is capable of determining two threshold values according to the desired demand of the embedding capacity requested by the user. Experimental results demonstrated that our adaptive steganographic algorithm produces insignificant visual distortion due to the hidden message. It provides high embedding capacity superior to that offered by a number of existing schemes. Our algorithm can resist the RS steganalysis attack, and it is statistically invisible for the attack of histogram comparison. The proposed scheme is simple, efficient and feasible for adaptive steganographic applications.

Reversible image steganographic scheme via predictive coding

The reversible image steganographic scheme in this study provides the ability to embed secret data into a host image and then recover the host image without losing any information when the secret data is extracted. In this paper, a reversible image steganographic scheme based on predictive coding is proposed by embedding secret data into compression codes during the lossless image compression. The proposed scheme effectively provides a lossless hiding mechanism in the compression domain. During the predictive coding stage, the proposed scheme embeds secret data into error values by referring to a hiding-tree. In an entropy decoding stage, the secret data can be extracted by referring to the hiding-tree, and the host image can be recovered during the predictive decoding stage. The experimental results show that the average hiding capacity of the proposed scheme is 0.992 bits per pixel (bpp), and the host image can be reconstructed without losing any information when the secret data is extracted.