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1

Reversible Data Hiding Scheme Based on Image Inpainting

Qin C., Wang Z. H., Chang C-C., Chen K. N.

Fundamenta Informaticae

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2012

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Vol. 120, nr 1

59-70

EN

Reversible/lossless image data hiding schemes provide the capability to embed secret information into a cover image where the original carrier can be totally restored after extracting the secret information. This work presents a high performance reversible image data hiding scheme especially in stego image quality control using image inpainting, an efficient image processing skill. Embeddable pixels chosen from a cover image are initialized to a fixed value as preprocessing for inpainting. Subsequently, these initialized pixels are repaired using inpainting technique based on partial differential equations (PDE). These inpainted pixels can be used to carry secret bits and generate a stego image. Experimental results show that the proposed scheme produces low distortion stego images and it also provides satisfactory hiding capacity.

2

Reversible Steganography for BTC-compressed Images

Chang C-C., Lin C-Y., Fan Y-H.

Fundamenta Informaticae

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2011

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Vol. 109, nr 2

121-134

EN

Reversible steganography becomes a popular hiding problem in recent years. A reversible steganographicmethod can reconstruct an original image without loss from the stego-image after extracting the embedded data. Unlike traditional reversible methods in which data is hidden in uncompressed images, we propose a reversible scheme for BTC (block truncation coding)- compressed images. The secret data embedded in the compressed image are more difficult to detect than in the uncompressed image. To achieve reversibility, the properties of side matching and BTCcompressed code are applied. The experimental results show that the proposed method is feasible for BTC-compressed images and can embed one more bit in each BTC-encoded block.

3

Preventing Cheating in Computational Visual Cryptography

Chang C-C., Chen T-H., Liu L-J.

Fundamenta Informaticae

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2009

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Vol. 92, nr 1-2

27-42

EN

Visual Cryptography (VC) has drawn much attention for providing the service of secret communication. Basically, VC is the process of encoding a secret into several meaningless shares and later decoding the secret by superimposing all or some of the shares without any computation involved. VC has been adopted to support some practical applications, such as image authentication, visual authentication, image hiding, and digital watermarking. Unfortunately, in many applications, VC has been shown to suffer from the "cheating problem" in which the disclosed secret image may be altered by malicious insiders who are called "cheaters." While ubiquitous computing has been well developed, it has recently occurred to people in both academia and industry that research could benefit more from computational VC by introducing light-weight computation costs in the decoding phase. In this paper, a simple scheme is proposed to conquer the cheating problem by facilitating the capability of share authentication. It is worthwhile to note that the proposed scheme can identify for certain whether cheating attacks have occurred or not, while other schemes that have the same objective frequently provide a vague answer. In addition, the proposed scheme effectively addresses the two main problems of VC, i.e., the inconvenience of meaningless share management and the challenge of achieving difficult alignment.

4

Novel Watermarking Authentication Schemes for Binary Images Based on Dual-Pair Block Pixel Patterns

Wang C-C., Chang C-C., Jan J-K.

Fundamenta Informaticae

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2009

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Vol. 90, nr 1-2

125-155

EN

In this paper, watermarking authentication schemes for binary images are investigated. Dual-Pair Blocks (DPBs), 2×2 blocks with two black and two white pixels, are employed as the basic units of information embedding. With 6 distinctive patterns obtained by pixel patterns, a DPB can be represented by a senary value as the embedding information. Variable length coding is adopted to enhance the information embedding capacity of the DPB. The secret key of the watermarking is a pseudo random function with a seed value, which selects DPBs for information embedding. Based on the aforementioned framework, two novel watermarking schemes are presented. The first one, named dual-pair block authentication (DPBA), is an irreversible one featuring high information embedding capacity, and well visual quality. The second scheme, named senary Huffman compression authentication (SHCA) scheme, supports reversible watermarking unique in the literature. Matching-pair technique is further employed both schemes to reduce the number of altered bits after watermarking for better visual quality. Experimental results show that, the DPBA scheme has the highest information embedding capacity on all comparing schemes. The average compression ratio of the reversible SHCA scheme is up to 38.96%. The average distortion rates per accessed DPB for the proposed DPBA and SHCA schemes are 0.485 and 0.46, respectively.

5

An Information-Hiding Scheme Based on Quantization-Based Embedding Technique

Lu T-C., Chang C-C., Liu Y-L.

Fundamenta Informaticae

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2009

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Vol. 91, nr 3-4

597-610

EN

Information hiding is a technique that embeds secret data in digital media for using in a variety of applications, including ownership protection, authentication, access control, annotation and so on. In this paper, we propose an information hiding scheme based on quantization-based embedding technique to conceal information in gray-scale image. The proposed scheme was tested with a variety of gray images. According to the experimental results, hidden information can be extracted correctly and quickly from the stego image. In addition, the stego image has only a little distortion compared with the cover image. The proposed scheme can not only hide a large amount of information in the cover image, but can also repair the stego image such that the repaired image is almost the same as the cover image.

6

An Image Authentication Based on Discrete Fourier Transform

Kieu T.D., Chang C-C.

Fundamenta Informaticae

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2009

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Vol. 97, nr 4

369-379

EN

The advances of network technologies and digital devices facilitate users to exchange multimedia data over the public networks. However, this also raises significant concerns about how to protect sensitive multimedia data from being illegally copied and unauthorized modifications. Thus, this paper proposes a fragile watermarking method to detect illegitimate alterations of the watermarked data. The proposed method embeds a grayscale watermark image into a grayscale cover image in a block-by-block manner by using discrete Fourier transform. Experimental results show that the proposedmethod can successfully and exactly detect and localize any tampered regions of the watermarked image.

7

A Fragile Digital Image Authentication Scheme Inspired by Wet Paper Codes

Chang C-C., Chou Y-C.

Fundamenta Informaticae

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2009

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Vol. 90, nr 1-2

17-26

EN

Image authentication is an important research topic of maintaining the integrity of digital image contents. Fragile image authentication is the technique for achieving the goal of image content integrity maintenance. This article presents a fragile image authentication scheme based on the concept of wet paper codes. The proposed scheme modifies dry pixels on an image to conceal an image signature. The proposed authentication scheme can exactly detect the tampered area on a tampered image. For saving computation cost of signature embedding, an exclusive-or operation is used in the proposed authentication scheme. The experimental results show that the proposedmethod not only has good visual quality of an authorized image but also successfully detects tampered areas on a tampered image.

8

Three-Phase Lossless Data Hiding Method for the VQ Index Table

Chang C-C., Lin C-Y., Hsieh Y-P.

Fundamenta Informaticae

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2008

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Vol. 82, nr 1-2

1-13

EN

Hiding Data in a cover image often applies a steganographic technique that makes the stego image appear as similar to the original cover image as possible. Conventional VQ-based (vector quantization) steganographic methods typically involve codeword replacements to hide secret bits. Such replacements may cause serious distortion or a perceptible block effect on the stego image. In this paper, we propose a three-phase steganographic method for the VQ index table. Instead of applying codeword replacements, the proposed method uses different coding schemes-SOC, SMVQ, and VQ-to imply the secret bits. The quality of the stego image generated by the proposed method is completely equal to that of the original cover image (i.e., the VQ cover image). Experimental results have shown that the proposed method has the best stego image quality compared with other methods. In addition, the proposed method provides adaptive embedding capacity and compression bit rate according to predefined thresholds.

9

High Capacity Data Hiding for Grayscale Images

Chang C-C., Chou Y-C., Kieu T.D.

Fundamenta Informaticae

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2008

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Vol. 86, nr 4

435-446

EN

High embedding capacity and low image distortion factors are main concerns of information hiding researchers. No scheme can achieve these two factors simultaneously. The purpose of achieving either high embedding capacity or low image distortion varies from application to application. This paper presents a high embedding capacity information hiding method for grayscale images. The proposed method converts binary secret data into secret digits in the base-5 numeral system first. Next, one secret digit in the base-5 numeral system is embedded into one cover pixel. The experimental results show that the proposed method can be used to embed two secret bits into one cover pixel with the imperceptible image distortion. Comparing with some other works, we found that our method indeed outperforms all others in terms of embedding capacity.

10

Adaptive Data Embedding Scheme Based on Similar and Dissimilar Clustering Strategies

Chang C-C., Lin C-C., Chen Y-C.

Fundamenta Informaticae

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2008

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Vol. 88, nr 1-2

23-45

EN

Embedding large amounts of secret data into a cover image with low distortion is an important research issue in steganography. The proposed scheme uses two clustering technologies - similar and dissimilar clustering - to enhance hiding capacity as provided by Du and Hsu’s scheme. In general, the hiding capacity of our proposed scheme is higher than that of Du and Hsu’s scheme, about 16 Kb for the same image quality. In addition, the image quality of our proposed scheme is more than provided by the schemes of either Du and Hsu’s or Shie et al., about 2 dB. Moreover, the distortion for each test image in our proposed scheme is always less than those caused by Du and Hsu’s and Shie et al.’s schemes. Experimental results confirm that the proposed scheme is significantly better than earlier works.

11

A Novel Cryptographic Key Assignment Scheme with ID-Based Access Control in a Hierachy

Huang H-F., Chang C-C.

Fundamenta Informaticae

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2008

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Vol. 84, nr 3-4

353-361

EN

The hierarchical cryptographic key assignment is used to assign cryptographic keys to a set of partially ordered classes so that the user in a higher class can derive the cryptographic key for users in a lower class. However, the existing secure schemes for the cryptographic key assignment in a hierarchy do not consider the situation where a user may be employed for only a period of time. If a user resigned from his position and he premeditatedly eavesdrops on data transmissions, then he can also decrypt some data to obtain useful messages. Thus, all messages are likely to be compromised throughout the system. In this paper, we propose a new cryptographic key assignment scheme in which the cryptographic keys are generated from the identity number of users. Our aim is to minimize the potential damage over a public network. Therefore, as a user who has resigned from his class premeditatedly eavesdrops on later messages, he cannot decrypt the message with his old keys. Moreover, in the proposed method, the key generation and key derivation are quite simple, and the number of the public/secret parameters for each authenticated user is fixed which differs from most previously proposed schemes.

12

A Large Payload Data Embedding Technique for Color Images

Chou Y-C., Chang C-C., Li K-M.

Fundamenta Informaticae

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2008

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Vol. 88, nr 1-2

47-61

EN

This paper proposes a large payload data embedding method for color images. Under the fast advancement of digital equipments, color images have become a common medium in many applications. A color image can be represented in different color systems, for instance, RGB and YUV color systems. The proposed method modifies the blue value of the color pixel in order to imply the secret data because the blue value is an insensitive color to human eyes. Furthermore, the number of secret bits that can be embedded into a cover pixel is dynamic so the proposed method tries to embed the secret data as many as possible. The proposed method can be applied to both RGB and YUV color systems. However, for anti-stegoanalysis reason, the RGB color system is suitable for the proposed high capacity data embedding method with lower image distortion. The experimental results show that the proposed method is superior to other methods we compared in terms of embedding capacity and visual quality.

13

VQ Codebook Searching Algorithm Based on Correlation Property

Chang C-C., Lu T-C., Ya J-B.

Fundamenta Informaticae

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2007

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Vol. 76, nr 1-2

39-57

EN

In this paper, we shall present two efficient codebook-matching schemes with a locally adaptive vector quantizer (LAVQ) and a search-ordering coding vector quantizer (SOCVQ) to be applied in the Vector Quantization (VQ) encoding system. The proposed codebook-matching schemes exploit the correlation property between adjacent image blocks so that the process of codebook matching can be speed up. Simulation results show that the time complexity of the proposed schemes is lower than those of PCA, Multipath TSVQ, and DPTSVQ. Moreover, the image quality of the proposed methods is close to those processed by the other methods.

14

Tolerant Key Assignment for Enforcing Complicated Access Control Policies in a Hierarchy

Chang Y-F., Chang C-C.

Fundamenta Informaticae

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2007

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Vol. 76, nr 1-2

13-23

EN

In 1998, Yeh et al. proposed a flexible key assignment scheme for enforcing complicated access control policies in a user matrix model. Later, Hwang indicated that Yeh et al.' scheme is susceptible to some security flaws. Thus, Lin et al. proposed a key assignment scheme for enforcing complicated access control policies in a hierarchy. However, there exist drawbacks in Lin et al.'s scheme: lack of efficiency and a large variation of the keys. Hence, we propose an efficient key assignment scheme in a hierarchy for enforcing the complicated access control policies. What is more, the secret key of one class is allowed to be changed several times without influencing the derivation key in our proposed scheme.

15

Secret Image Hiding and Sharing Based on the (t,n)-Threshold

Chang C-C., Lin C-Y., Tseng C-S.

Fundamenta Informaticae

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2007

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Vol. 76, nr 4

399-411

EN

This study proposes a new secret image sharing method based on the ( t, n)-threshold. The sharing method is completed through three main steps: (1) quantizing the secret image, (2) generating n shadows from the quantized image, and (3) sharing the n shadows among n cover images. Our goal is both to attain good stego-image and secret image quality preservation effects and to limit the size of each shadow image down to 1/ t of that of the secret image for convenient transmission and storage. In the first step, the secret image is divided into non-overlapping 4 × 4 blocks that are quantized according to the results of block testing. Each block, after the block testing procedure, is judged to be either a smooth block or a non-smooth one. Smooth blocks can be neatly restored after being hidden into the cover image, while non-smooth blocks can be somewhat lossy, but such modification is perceptually invisible. The second step is to apply Shamir's ( t,n)-threshold, which uses a ( t-1)-degree polynomial to generate n shadows so that the secret image can be restored from any t out of n shadows. The last step involves a modulo operation to hide the n shadows in n cover images. According to our experimental results, the PSNR values of the reconstructed secret images by our method center around 39 dB, outperforming other recent methods.

16

Full-Searching-Equivalent Vector Quantization Method Using Two-Bounds Triangle Inequality

Chang C-C., Chen C-C.

Fundamenta Informaticae

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2007

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Vol. 76, nr 1-2

25-37

EN

The encoding process of vector quantization (VQ) is indeed computational complex and time consuming. Compared with actual Euclidean distance computation, some inequalities can generate estimations with less computation to filter out the impossible codevectors as well as to reduce the computation time. In this paper, we introduce a new estimation for the Euclidean distance using two-bounds triangle inequality. The experimental results show that our proposed scheme can reduce Euclidean distance computation by 71% to 94% for full search. Having been proved, our proposed scheme can reduce the computing time by 42% to 51%.

17

An Image Retrieval Method Based on Color-Complexity and Spatial-Histogram Features

Wu H-C., Chang C-C.

Fundamenta Informaticae

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2007

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Vol. 76, nr 4

481-493

EN

This paper proposes two kinds of image features. One feature is the spatial-histogram feature. It combines the color histogram feature and the information about the dimensional position of pixels in an image to record the distribution of the pixels' colors that are present in different spatial positions within an image. The other image feature proposed in this paper is the color-complexity feature, which can be used to describe the change of pixel colors in the image. From the experimental results, ANMRR value is provided and we observe that the image retrieval system based on these two kinds of image features can provide a fairly good accuracy rate in image retrieval. Moreover, it has the capacity to tolerate errors; that is, for images that are damaged by rotation, shift, or color variant attacks, their similar image pairs can still be retrieved from the image database. Thus, the accuracy and flexibility of the image retrieval system are drastically improved.

18

A Novel Image Hiding Scheme Based on VQ and Hamming Distance

Chang C-C., Tai W-L., Lin C-C.

Fundamenta Informaticae

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2007

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Vol. 77, nr 3

217-228

EN

Data hiding is popularly employed in protecting the copyright, secret information and communication secretly with the convenience of network communication. In order to reduce the amount the transmitted data via network, VQ (vector quantization) is applied to compressing the transmitted data. Since VQ is a low-bit-rate compression scheme, it is difficult to find large redundant hiding space and to get stego-images with high quality for hiding data in VQ-based compressed images. A hiding method for VQ-based compressed images is proposed in this paper according to the Hamming distance between the index values of codewords. Our method makes hiding data more effective and provides stego-images with higher quality than other conventional methods. Experimental results demonstrate the effectiveness and the feasibility of our method.

19

Spatial Domain Image Hiding Scheme Using Pixel-Values Differencing

Chang C-C., Chuang J-C., Hu Y-C.

Fundamenta Informaticae

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2006

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Vol. 70, nr 3

171-184

EN

In this paper, we present a spatial domain Image hiding scheme that embeds secret data in a gray-level image. Our scheme is inspired from Wu and Tsai's scheme that embeds secret bits in the difference values of consecutive pixels. To improve the hiding capacity of their scheme, the overlapping concept is proposed to produce more difference values from the cover image in this paper. Experimental results show that our scheme provides an average hiding capacity gain of 84.16% over Wu and Tsai's scheme while maintaining satisfactory image quality.

20

Reversible Data Embedding Based on Prediction Approach for VQ and SMVQ Compressed Images

Chang C-C., Lin C-Y.

Fundamenta Informaticae

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2006

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Vol. 74, nr 2,3

189-207

EN

Reversible steganography allows an original image that has gone through the embedding process to be completely restored after the extraction of the embedded data. In this paper, we propose a reversible scheme with a high embedding capacity for VQ compressed images. Our reversible method is based on a prediction strategy and takes advantage of the local characteristics of the image. Since the location map is usually a necessary part of a reversible scheme, two methods, shifting and relocating, are also proposed to reduce the size of the location map. As the experimental results show later, our method outperforms previous schemes in terms of embedding capacity and image quality. To be more specific, with low distortion, the embedding capacity of the proposed methods can be higher than one bit per index value.