Showing papers on "Visual cryptography published in 2012"

An Extended Visual Cryptography Algorithm for General Access Structures

Abstract: Conventional visual secret sharing schemes generate noise-like random pixels on shares to hide secret images. It suffers a management problem, because of which dealers cannot visually identify each share. This problem is solved by the extended visual cryptography scheme (EVCS), which adds a meaningful cover image in each share. However, the previous approaches involving the EVCS for general access structures suffer from a pixel expansion problem. In addition, the visual cryptography (VC)-based approach needs a sophisticated codebook design for various schemes. In this paper, we propose a general approach to solve the above- mentioned problems; the approach can be used for binary secret images in noncomputer-aided decryption environments. The pro- posed approach consists of two phases. In the first phase, based on a given access structure, we construct meaningless shares using an optimization technique and the construction for conventional VC schemes. In the second phase, cover images are added in each share directly by a stamping algorithm. The experimental results indicate that a solution to the pixel expansion problem of the EVCS for GASs is achieved. Moreover, the display quality of the recovered image is very close to that obtained using conventional VC schemes.

Comment on “Cheating Prevention in Visual Cryptography”

Abstract: Visual cryptography (VC), proposed by Naor and Shamir, has numerous applications, including visual authentication and identification, steganography, and image encryption. In 2006, Horng showed that cheating is possible in VC, where some participants can deceive the remaining participants by forged transparencies. Since then, designing cheating-prevention visual secret-sharing (CPVSS) schemes has been studied by many researchers. In this paper, we cryptanalyze the Hu-Tzeng CPVSS scheme and show that it is not cheating immune. We also outline an improvement that helps to overcome the problem.

Optimal Contrast Greyscale Visual Cryptography Schemes with Reversing

Abstract: Visual cryptography scheme (VCS) is an encryption technique that utilizes human visual system in recovering secret image and it does not require any complex calculation. However, the contrast of the reconstructed image could be quite low. A number of reversing-based VCSs (or VCSs with reversing) (RVCS) have been proposed for binary secret images, allowing participants to perform a reversing operation on shares (or shadows). This reversing operation can be easily implemented by current copy machines. Some existing traditional VCS schemes without reversing (nRVCS) can be extended to RVCS with the same pixel expansion for binary image, and the RVCS can achieve ideal contrast, significantly higher than that of the corresponding nRVCS. In the application of greyscale VCS, the contrast is much lower than that of the binary cases. Therefore, it is more desirable to improve the contrast in the greyscale image reconstruction. However, when greyscale images are involved, one cannot take advantage of this reversing operation so easily. Many existing greyscale nRVCS cannot be directly extended to RVCS. In this paper, we first give a new greyscale nRVCS with minimum pixel expansion and propose an optimal-contrast greyscale RVCS (GRVCS) by using basis matrices of perfect black nRVCS. Also, we propose an optimal GRVCS even though the basis matrices are not perfect black. Finally, we design an optimal-contrast GRVCS with minimum number of shares held by each participant. The proposed schemes can satisfy different user requirement, previous RVCSs for binary images can be viewed as special cases in the schemes proposed here.

A Novel Anti phishing framework based on visual cryptography

Abstract: With the advent of internet, various online attacks has been increased and among them the most popular attack is phishing. Phishing is an attempt by an individual or a group to get personal confidential information such as passwords, credit card information from unsuspecting victims for identity theft, financial gain and other fraudulent activities. Fake websites which appear very similar to the original ones are being hosted to achieve this. In this paper we have proposed a new approach named as "A Novel Anti-phishing framework based on visual cryptography "to solve the problem of phishing. Here an image based authentication using Visual Cryptography is implemented. The use of visual cryptography is explored to preserve the privacy of an image captcha by decomposing the original image captcha into two shares (known as sheets) that are stored in separate database servers(one with user and one with server) such that the original image captcha can be revealed only when both are simultaneously available; the individual sheet images do not reveal the identity of the original image captcha. Once the original image captcha is revealed to the user it can be used as the password. Using this website cross verifies its identity and proves that it is a genuine website before the end users.

A Probabilistic Model of $(t,n)$ Visual Cryptography Scheme With Dynamic Group

Abstract: The (t, n) visual cryptography (VC) is a secret sharing scheme where a secret image is encoded into n transparencies, and the stacking of any t out of n transparencies reveals the secret image. The stacking of t - 1 or fewer transparencies is unable to extract any information about the secret. We discuss the additions and deletions of users in a dynamic user group. To reduce the overhead of generating and distributing transparencies in user changes, this paper proposes a (t, n) VC scheme with unlimited n based on the probabilistic model. The proposed scheme allows n to change dynamically in order to include new transparencies without regenerating and redistributing the original transparencies. Specifically, an extended VC scheme based on basis matrices and a probabilistic model is proposed. An equation is derived from the fundamental definitions of the (t, n) VC scheme, and then the (t, ∞) VC scheme achieving maximal contrast can be designed by using the derived equation. The maximal contrasts with t = 2 to 6 are explicitly solved in this paper.

Efficient Construction for Region Incrementing Visual Cryptography

Abstract: A region incrementing visual cryptography scheme (RIVCS) deals with the sharing of an image consisting of multiple regions with different secrecy levels, which can be incrementally revealed as the number of shares increases. The encoding basis matrices of RIVCS for an image containing three to five regions have been reported in the literature, but no construction method has ever been studied. We develop a novel and efficient construction for RIVCS using linear programming in this paper. The proposed integer linear program aims at the minimization of the pixel expansion under the constraints for being a RIVCS. Experimental results demonstrate the feasibility, applicability, and flexibility of our construction. The pixel expansions and contrasts derived from our scheme are also better than the previous results.

A Weak Security Notion for Visual Secret Sharing Schemes

Abstract: We propose a weak security notion for visual secret sharing (VSS) schemes. Under such a weak security notion, VSS schemes are designed to be secure against attackers' eyesight, but are not unconditionally secure, in general. In this paper, we theoretically discuss the relation between unconditionally secure (US) and weakly secure (WS) VSS schemes and present two constructions of WS-VSS schemes for color images. We show that WS-VSS schemes can achieve clearer color reproduced images with a smaller pixel expansion compared to those using US-VSS schemes, while we clarify that the basis matrices in both types of VSS schemes for black-white binary images are the same. These results suggest that the proposed VSS schemes can be regarded as ramp (or nonperfect) VSS schemes for color secret images.

Hybrid Steganography using Visual Cryptography and LSB Encryption Method

Abstract: The biggest threat in the data transfer is through any medium is, the chance for it being hacked. Any information, these days are hackable. So utmost care has to be taken for any communication to be done, in particular, if confidential. The so claimed most sheltered data have also been hacked nowadays. The digital watermarking is a widely used method for information hiding to authenticate as well as secure the content in an image. This paper describes a hybrid watermarking technique to embed a secret message into an image using visual cryptography and SLSB(Selected Least Significant Bit) encryption techniques. This paper becomes very special in few aspects, all of them are explained in a detailed way in the chapters.

A novel visual secret sharing scheme without image size expansion

Abstract: Over the past few years, increasing concern about the privacy of information shared in computer systems has increased interest in data security. Visual cryptography is a secure secret sharing scheme that divides secret images into shares which on their own reveal no information of the original secret image. Recovery of the secret image can be performed by superimposing the shares. Hence, the process does not require any special software or hardware for cryptographic computations. However, loss of resolution and contrast, and also the image size expansion which results in the need for storage space, are resulting problems and have been the focus of many researchers. In this paper, we propose a novel visual secret sharing scheme without image size expansion. Compared to other schemes of visual cryptography, our perfectly secure scheme not only does not have pixel expansion, but also provides a high quality recovered image.

New visual Steganography scheme for secure banking application

Abstract: Core banking is a set of services provided by a group of networked bank branches. Bank customers may access their funds and perform other simple transactions from any of the member branch offices. The major issue in core banking is the authenticity of the customer. Due to unavoidable hacking of the databases on the internet, it is always quite difficult to trust the information on the internet. To solve this problem of authentication, we are proposing an algorithm based on image processing, improced steganography and visual cryptography. This paper proposes a technique of encode the password of a customer by improved Steganography, most of the steganographic techniques use either three or four adjacent pixels around a target pixel whereas the proposed technique is able to utilize at most all eight adjacent neighbors so that imperceptibility value grows bigger and then dividing it into shares. Total number of shares to be created is depending on the scheme chosen by the bank. When two shares are created, one is stored in the Bank database and the other is kept by the customer. The customer has to present the share during all of his transactions. This share is stacked with the first share to get the original image. Then decoding method is used to take the hidden password on acceptance or rejection of the output and authenticate the customer.

Extended visual cryptography for color images using coding tables

Abstract: Visual cryptography (VC) schemes encrypt a secret image into two or more cover images, called shares. The secret image can be reconstructed by stacking the shares together, with no complex cryptographic calculations. This paper proposes a new VC scheme for color images. The shares generated are similar to the cover images, thereby reducing the suspicion of data encryption. The proposed scheme makes use of Jarvis error filter, a key table and specialized tables for coding. High visual quality is achieved as up to 50 percent of the secret image can be recovered.

Design of hierarchical visual cryptography

Abstract: This paper describes the concept of hierarchical visual cryptography. The key idea behind hierarchical visual cryptography is to encrypt the secret information in number of levels. As the number of levels in hierarchical visual cryptography increases, the secrecy of data tends to increase. An intelligent authentication system is also proposed using hierarchical visual cryptography. The shares generated out of Hierarchical visual cryptography are found to be random giving no information. The expansion ratio is also reduced to 1:2 from 1:4.

Digital image ownership verification based on spatial correlation of colors

Abstract: In this paper, a spatial domain digital image copyright protection scheme based on Visual Cryptography (VC) and Spatial Correlation of Colors (SCC) is proposed. A binary feature matrix, extracted from the spatial correlation of host image, is used to split the watermark into two noisy binary images called shares. One of them is generated during watermark embedding phase and is registered with a trusted third party. The other is extracted during watermark extraction phase. Both these shares are combined to recover hidden watermark. When compared to the related works, the proposed scheme reduces the probability of false positives; reduces the size of shares and improves the quality of extracted watermark. Experimental results prove that the scheme is also robust to wide range of attacks. (5 pages)

Enhancing the perceived visual quality of a size invariant visual cryptography scheme

Abstract: Two of the main areas of research in visual cryptography have been on improving the visual quality of the recovered image and in reducing the pixel expansion of the shares. This paper addresses both of these visual cryptography issues. First, a method to enhance the perceived visual quality of the recovered image using various image filtering techniques is presented. In particular, these image filtering techniques are used to enhance the local and global contrasts of a grayscale image. Second, a multi-pixel block size invariant visual cryptography scheme that maintains the relative density of local neighboring pixels is proposed. This method encrypts blocks of pixels based on whether the total number of black pixels within the respective blocks is above or below a certain threshold. In conjunction, these approaches effectively improve on the perceived visual quality of a recovered visual cryptography image.

Image hatching for visual cryptography

Abstract: Image hatching (or nonphotorealistic line-art) is a technique widely used in the printing or engraving of currency. Diverse styles of brush strokes have previously been adopted for different areas of an image to create aesthetically pleasing textures and shading. Because there is no continuous tone within these types of images, a multilevel scheme is proposed, which uses different textures based on a threshold level. These textures are then applied to the different levels and are then combined to build up the final hatched image. The proposed technique allows a secret to be hidden using Visual Cryptography (VC) within the hatched images. Visual cryptography provides a very powerful means by which one secret can be distributed into two or more pieces known as shares. When the shares are superimposed exactly together, the original secret can be recovered without computation. Also provided is a comparison between the original grayscale images and the resulting hatched images that are generated by the proposed algorithm. This reinforces that the overall quality of the hatched scheme is sufficient. The Structural SIMilarity index (SSIM) is used to perform this comparison.

Robust video watermarking scheme based on visual cryptography

Abstract: A novel video watermarking scheme based on visual cryptography and scene change detection in discrete wavelet transform domain is proposed We start with a complete survey of the current image and video watermarking technologies, and have noticed that majority of the existing schemes are not capable of resisting all attacks We propose the idea to use different parts of a single watermark into different scenes of a video for generation of the owner's share from the original video based on the frame mean in same scene and the binary watermark, and generation of the identification share based on the frame mean of probably attacked video These two shares after stacking can reveal the copyright ownership Experiments are conducted to verify the robustness through a series of experiments

Dwt-svd based secured image watermarking for copyright protection using visual cryptography

Abstract: In this paper, a new robust watermarking technique for copyright protection based on Discrete Wavelet Transform and Singular Value Decomposition is proposed. The high frequency subband of the wavelet decomposed cover image is modified by modifying its singular values. A secret key is generated from the original watermark with the help of visual cryptography to claim the ownership of the image. The ownership of the image can be claimed by superimposing this secret key on the extracted watermark from the watermarked image. The robustness of the technique is tested by applying different attacks and the visual quality of the extracted watermark after applying these attacks is good. Also, the visual quality of the watermarked image is undistinguishable from the original image.

Dual Image Watermarking Scheme based on Singular Value Decomposition and Visual Cryptography in Discrete Wavelet Transform

Abstract: There is wide interest in multimedia security and copyright protection due to the explosion of data exchange in the Internet and the extensive use of digital media. An image watermarking scheme based on singular value decomposition and visual cryptography in discrete wavelet transform is proposed. We start with a survey of the current image watermarking technologies, and have noticed that majority of the existing schemes are not capable of resisting all attacks. We propose the idea to use of singular value decomposition and visual cryptography in discrete wavelet transform such that the primary watermarking scheme based on singular value decomposition in the discrete wavelet transform is empowered by the secondary watermarking scheme based on visual cryptography in discrete wavelet transform. Experiments are conducted to verify the robustness through a series of experiments.

On the equivalence of two definitions of visual cryptography scheme

Abstract: A visual cryptography scheme (VCS) is a secret sharing method, for which the secret can be decoded by human eyes without needing any cryptography knowledge nor any computation. To the best of our knowledge, there are two different definitions of basis matrix (k,n)-VCS. The definition of unconditional secure basis matrix (k,n)-VCS is the generally accepted one, and has been widely used since the pioneer work of Naor and Shamir in 1994, while the definition of stacking secure basis matrix (k,n)-VCS is relatively new, and has been used in many studies in recent years. Our study shows that the above two definitions are actually equivalent. Furthermore, we generalize the equivalence relation to general access structure basis matrix VCS and general access structure size invariant VCS. But the equivalence relation does not hold for non-basis matrix (k,n)-VCS.

Two-out-of-two color matching based visual cryptography schemes.

Abstract: Visual cryptography which consists in sharing a secret message between transparencies has been extended to color prints. In this paper, we propose a new visual cryptography scheme based on color matching. The stacked printed media reveal a uniformly colored message decoded by the human visual system. In contrast with the previous color visual cryptography schemes, the proposed one enables to share images without pixel expansion and to detect a forgery as the color of the message is kept secret. In order to correctly print the colors on the media and to increase the security of the scheme, we use spectral models developed for color reproduction describing printed colors from an optical point of view.

Image Watermarking Scheme based on Visual Cryptography in Discrete Wavelet Transform

Abstract: Multimedia security and copyright protection have become wide interest due the explosion of data exchange in the Internet and the extensive use of digital media. We propose an image watermarking scheme based on visual cryptography in discrete wavelet transform. A complete survey of the current image watermarking technologies was done and has been noticed that majority of the existing schemes are not capable of resisting all attacks. We propose the idea to use different parts of a single watermark into different regions of the image for generation of the owner’s share from the low frequency subband of the original image based on the binary watermark, and comparing the global mean value of pixels in the same subband and the local mean of the same subband, and generation of the identification share based on comparing the global mean and the local mean of the low frequency subband of the controversial image. These two shares after stacking can reveal the copyright ownership. Experiments are conducted to verify the robustness through a series of experiments. General Terms Watermarking

Sheltered iris attestation by means of Visual Cryptography (SIA-VC)

Abstract: Biometric techniques consists of uniquely identifying a person based on their physical characteristic or behavioral characteristic. It is mainly used for authentication purpose. Iris is one of the most powerful technique among all biometrics because of its uniqueness and stability. For authentication, the feature template in the database and the user template should be the same. Storing the template in the database securely is troublesome, because it can be compromised. In order to overcome this issue, in this paper a new method for securely storing the template in the database is proposed. This method uses Visual Cryptography (VC) concept and will generate shares, that shares will be stored in the database. The proposed Visual Cryptography fashion will generate meaningful shares which overcomes the problem in existing methods. Thus this new operandi will provide a great means of security and an extravagance layer for endorsement.