Improved Halftone Visual Cryptography by Random Grids

ENHANCING home security through visual CRYPTOGRAPHY

Visual secret sharing is the technique that divide the secret image into n multiple shares. Each share constitutes some information and when k shares out of n stack together the secret will reveal. However, less than k shares are not work. Sharing is the idea from secret sharing scheme that was presented in 1975 by Adi Shamir. The beauty of the visual secret sharing scheme is its decryption process i.e. To decrypt the secret using Human Visual System (HVS) without any computation. Visual cryptography is presented by Noar and Shamir in 1995 including also visual secret sharing. The resultant secret recover through this scheme is double in size of the original secret [17]. We have proposed the new algorithms for the (2, 2) visual cryptography and (3, 3) visual secret sharing. Our proposed schemes are for gray scale image and by stacking the shares, the resultant image achieved in same size with original secret image and Its shadow Image. We used randomization and pixel reversal approach in all methods.

Obscuring the important message before disseminating become obligatory. In a traditional (n, k) threshold visual secret sharing(VSS), size of the reassembled secret is more than the original secret image and the reassembled secret image consist of lots of noise. An (n, k)-threshold visual secret sharing system is more appropriate for binary, gray and color secret images when the reassembled secret is identical with the original secret in size and content. In the former techniques, the reassembled binary image loses contrast and the gray and color image are reassembled with a huge amount of noise which is greater in size w.r.t original secret image. The proposed approach significantly improve the quality and constructs original size of the reassembled secret image

Now a days, most of our data is travelled over internet so the security of that data is most important. Visual cryptography plays a very crucial role for security of image based secret. Visual cryptography encrypts the image in to shares and in decryption process all shares are stacked together to reveal the secret image. Here we are proposing a new scheme for color share generation. In this scheme R, G and B component is extracted from color image then apply gray share generation algorithm on R component and make n number of R gray shares then all shares are combine with B and G component to make color shares. At decryption side B and G component is extracted from all shares and then combine all r gray share to make r component and after that all R, G and B is combined to revealed the secret image. Decrypted secret image has same size as original secret image.

The traditional cheating prevention is usually based on visual cryptography (VC), in which the constructed image is bigger than the secret image because of the pixel expansion. In this paper, we studied the cheating problems in visual secret sharing (VSS) by random grids (RG) which can prevent the cheating activities with no pixel expansion. We considered the attacks of collusive cheaters who may deviate from the scheme in any way. We presented the cheating method and applied it on attacking existent n-out-of-n VSS scheme based on RG. Then we proposed one cheat-preventing scheme that can prevent the cheating activity upon.

Traditional k out of n visual cryptography scheme has been proposed to encrypt single secret image into n shares where only k or more shares can decode the secret image. Many existing schemes on visual cryptography are restricted to consider only binary images as secret which are not appropriate for many important applications. Store-and-Forward telemedicine is one such application where medical images are transmitted from one site to another via electronic medium to analyze the patient's clinical health status. The main objective of Store-and-Forward telemedicine is to provide remote clinical services via two-way communication between the patient and the healthcare provider using electronic medical image, audio and video means. In this paper, a new XOR based Continuous-tone Multi Secret Sharing scheme suitable for store-and-forward telemedicine is proposed to securely transmit the medical images. It also eliminates basic security constraints of VC like pixel expansion in shares/recovered secret images, random pattern of shares, explicit codebook requirement, lossy recovery of secret and limitation on number of secret and shares. Proposed approach is n out of n multi secret sharing scheme which is able to transmit n secret images simultaneously. All secrets could be revealed only after some computations with all n shares and one master share. Master share has been created with the secret key at encoding phase and it can be regenerated at the time of decoding using same secret key. Here all shares are meaningful in continuous-tone which may provide confidentiality to medical images during transmission. Proposed approach not only preserves all basic characteristics of traditional VC but also increases the capacity of secret image sharing. From the experiments we found that irrespective of visible contents of the shares, the probability of getting back the pixel values of respective original secret images at the receiver end is very high.

Threshold visual secret sharing by random grids

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.

An attempt is made for improvement of secret image invisibility in circulation images with dyadic wavelet based data hiding with run-length coded secret images of which location of codes are determined by random number. Through experiments, it is confirmed that secret images are almost invisible in circulation images. Also robustness of the proposed data hiding method against data compression of circulation images is discussed. Data hiding performance in terms of invisibility of secret images which are embedded in circulation images is evaluated with the Root Mean Square difference between the original secret image and extracted one from the circulation images. Mean while the conventional Multi- Resolution Analysis (MRA) based data hiding is attempted with a variety of parameters, level of MRA and the frequency component location of which secret image is replaced to it and is compared to the proposed method. It is found that the proposed data hiding method is superior to the conventional method. Also the conventional data hiding method is not robust against circulation image processing.

Steganography is the art of hiding secret data in a medium whereas visual-cryptography is a cryptographic technique where a full image is encrypted. The security of image steganography depends on the secret key set which is used for embedding the secret image. If the secret key is exposed, the secret image can be retrieved. To solve this security issue we propose a new type of steganography method using visual cryptography. In this method, text and image are used as a secret message and image for the cover object. 24-bit RGB color images are used as both secret and cover images. In this method, we use a new image namely share1 which converts a secret image to a totally different image called share2 image. Typically, knowing the extraction method, people can retrieve the secret message easily. A pseudorandomly generated image is used as a key for visual encryption and this ensures the extra layer of security. By this proposed method, we ensure more secured image steganography.

Conventional visual cryptography (VC) suffers from a pixel-expansion problem, or an uncontrollable display quality problem for recovered images, and lacks a general approach to construct visual secret sharing schemes for general access structures. We propose a general and systematic approach to address these issues without sophisticated codebook design. This approach can be used for binary secret images in non-computer-aided decryption environments. To avoid pixel expansion, we design a set of column vectors to encrypt secret pixels rather than using the conventional VC-based approach. We begin by formulating a mathematic model for the VC construction problem to find the column vectors for the optimal VC construction, after which we develop a simulated-annealing-based algorithm to solve the problem. The experimental results show that the display quality of the recovered image is superior to that of previous papers.

Conventional visual secret sharing (VSS) schemes generate noise-like random pixels on shares to hide secret images. However, these schemes suffer from two problems, one related to security and one related to management. First, the noise-like shares arouse suspicion, which leads to security problems for participants who are involved in a VSS scheme. Second, participants cannot visually identify each share, especially if they hold more than one share simultaneously, which leads to the management problem. To address the management problem previous researchers developed extended visual cryptography schemes that add a meaningful cover image on each share. Generally, however, these approaches introduce a more serious pixel expansion problem than conventional VSS schemes. In addition, there are still many noise-like shares, which do not effectively reduce the security problems. This paper proposes a natural-image-based secret image sharing scheme (NSISS) that can share a color secret image over n - 1 arbitrary natural images and one noise-like share image. Instead of altering the contents of the natural images, the encryption process extracts feature images from each natural image. In such a way, the unaltered natural images are innocuous, thus greatly reducing the security problem. Experimental results indicate that the proposed approach is an excellent solution for solving the management and security problems. Moreover, the proposed approach avoids the pixel expansion problem and makes it possible to totally recover the secret images.

The world has become very much dependent on electronic devices and internet with the advancement of new technologies. So, security is also becoming a very vital issue as we share all our details through different electronic mediums to internet. Cryptography is a well known technique of hiding secret data. Visual Cryptography (VC) is a special type of cryptography where we can securely transmit secret data over different transmission mediums. Various visual cryptography schemes have been formulated to carry out the secure transmission of images efficiently. Visual Cryptography provides techniques to share an image efficiently over various internet services. In visual cryptography an image is broken into a number of share images which are later stacked upon to generate the original image. Out of various schemes some have shown very promising results with or without a small increase in the final image dimension which is also referred as pixel expansion. The proper alignment of the distributed shares reveals the original secret image. In this paper we provide a state-of-the-art review and analysis of the several existing schemes of Visual Cryptography.

------------------------------------------------------------ABSTRACT--------------------------------------------------------Information security becomes more and more important while the internet communication grows up. Visual secret sharing (VSS) schemes hide secret images in shares that are either printed on transparencies or are encoded and stored in a digital form. Conventional visual secret sharing schemes suffers from a management problem, so that dealers cannot identify each share visually The approaches involving the EVCS for GAS suffers from a pixel expansion problem and also needs a sophisticated various encryption schemes. This paper presents natural image based visual secret sharing scheme that shares secret images via various carrier media to protect the secret and the participants during the transmission phase. The proposed (n, n) NVSS scheme can share one digital secret image over n -1 arbitrary selected natural images (called natural shares) and one noise-like share . The natural shares can be photos or hand-painted pictures in digital form or in printed form. The noise-like share is generated based on these natural shares and the secret image -------------------------------------------------------------------------------------------------------------------------------------Date of Submission: 03-April-2015 Date of Accepted: 30-April-2015 --------------------------------------------------------------------------------------------------------------------------------------

This article presents the method of recursive information hiding of secret images by random grids, which hides the additional secret information in the shares of the larger secret in a recursive manner. The proposed method increases the information conveyed per bit of the shares to nearly 100 percent, and has the size of each share the same as that of the original secret image without any expansion. The smaller size of the shares makes their further processing, such as storage and distribution, more efficient.