Showing papers on "Visual cryptography published in 2001"

Improved Schemes for Visual Cryptography

Abstract: A (k,n)-threshold visual cryptography scheme ((k,n)-threshold VCS, for short) is a method to encode a secret image SI into n shadow images called shares such that any k or more shares enable the “visual” recovery of the secret image, but by inspecting less than k shares one cannot gain any information on the secret image. The “visual” recovery consists of xeroxing the shares onto transparencies, and then stacking them. Any k shares will reveal the secret image without any cryptographic computation. In this paper we analyze visual cryptography schemes in which the reconstruction of black pixels is perfect, that is, all the subpixels associated to a black pixel are black. For any value of k and n, where 2\leq k\leq n, we give a construction for (k,n)-threshold VCS which improves on the best previously known constructions with respect to the pixel expansion (i.e., the number of subpixels each pixel of the original image is encoded into). We also provide a construction for coloured (2,n)-threshold VCS and for coloured (n,n)-threshold VCS. Both constructions improve on the best previously known constructions with respect to the pixel expansion.

An optical watermarking solution for authenticating printed documents

Abstract: We present a novel and simple optical watermarking system aiming at overriding some practical problems when the state-of-the art digital watermarking techniques are applied to authenticate printed documents. We name our technique optical watermarking differing from traditional digital watermarking in the sense that the watermark extraction is done by some optical and visual means like a photocopier, while no digitization is required. The system security is guaranteed by adopting a content-based key share scheme originated from visual cryptography. The non-obtrusiveness effect of the watermarked document is achieved by modulating the watermark into a higher resolution grating level. Experimental results demonstrate the availability and practicality of the proposed approach.

A copyright protection scheme of images based on visual cryptography

Abstract: This paper proposes a new scheme for effective protection of the intellectual property rights of digital images. Advantage is taken of visual cryptography to construct a master share from a digital image, and there is an ownership share for each copyright. After stacking of these two shares, the ownership information can be recovered directly by the naked eye without any computation. The method proposed will not change the host image and can be invisible, and moreover it can cast multiple ownerships into an image independently. Moreover, the method has high security, so that pirates and attackers will be unable to detect ownership information and fake the ownership of an image. Experimental results show that, after JPEG lossy compression, blurring, noise adding and cropping attacks, the ownership can still be robustly detected from the host image by the new method.

A technique for sharing a secret color image

Abstract: The present invention is related with ""Information Security"". A color image hiding technique developed based on Visual Cryptography is hereby proposed. The technique can very effectively hide a secret color image between any two randomly selected color images having certain significance. In other words, the two color images are used to camouflage the secret image and, therefore, may individually be owned by two participants sharing the secret. When the secret image needs to be restored, the two participants need only to provide each of the camouflaging image them possesses before. By means of simple overlapping and rather simple calculations, the secret image can be restored from the two camouflaging images. The present invention has a high security. It is impossible to restore the secret image if any one of the camouflaging images is not available. Note: The present invention is in the area of ""Information Security"". The related professional advise or assistance may be obtained from ""Information Security Society of the Republic of China"".

The General Neural-Network Paradigm for Visual Cryptography

Abstract: This paper proposes the general paradigm to build Q'tron neural networks (NNs) for visual cryptography. Given a visual encryption scheme, usually described using an access structure, it was formulated as a optimization problem of integer programming by which the a Q'tron NN with the so-called integer-programming-type energy function is, then, built to fulfill that scheme. Remarkably, this type of energy function has the so-called known-energy property, which allows us to inject bounded noises persistently into Q'trons in the NN to escape local minima. The so-built Q'tron NN, as a result, will settle down onto a solution state if and only if the instance of the given encryption scheme is realizable.

New Results on the Randomness of Visual Cryptography Schemes

Abstract: Visual cryptography schemes have been introduced in 1994 by Naor and Shamir as a mean to share images among a given group of participants. A visual cryptography scheme (VCS) for a set P of n participants encodes a secret image into n shadow images called shares each of which is given to a distinct participant. Certain qualified subsets of participants can recover the secret image, whereas forbidden subsets of participants have no information on the secret image. The shares given to participants in X ⊑ P are xeroxed onto transparencies. If X is qualified then the participants in X can visually recover the secret image by stacking their transparencies without any cryptography knowledge and without performing any cryptographic computation.

Visual cryptography based on optical interference encryption technique

Abstract: In this paper, we proposed a new visual cryptography scheme based on optical interference that can improve the contrast and signal to noise ratio of reconstructed images when compared to conventional visual cryptography methods. The binary image being encrypted is divided into any number of n slides. For encryption, randomly independent keys are generated along with another random key based on a XOR process of random keys. The XOR process between each divided image and each random key produces the encryption of n encrypted images. These encrypted images are then used to make encrypted binary phase masks. For decryption, the phase masks are placed on the paths of a Mach-Zehnder interferometer.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A known-energy neural network approach for visual cryptography

Abstract: This paper introduces the so-called known-energy system based on the Q'tron neural network (NN) model, and applies it to visual cryptography. With a known-energy system, the NN intrinsically performs a goal-directed search, meaning that the NN will settle down only when its state fulfils the dedicated goal. The noise injection mechanism that makes the NN to work in such a manner is discussed. The NN built for visual cryptography in the paper is modeled as a known-energy system. The approach is completely different from the traditional ones, and the so-built NN can be used to cope with complex encrypting structures of visual cryptography. Experiments show that its result is good.

Evaluation of correlation in optical encryption by using visual cryptography

Abstract: Visual cryptography made it possible to decrypt the information encrypted by thresholding scheme not with digital system but with human vision system. This method, however, has some limit in it because of the rack of resolution in both the spatial and amplitude domain. Optical visual cryptography, which used laser system instead of human eyesight, was proposed by conjunction of the optical theory with the cryptography. However, it also had some difficulties because it did not overcome the existing problem of visual cryptography completely. The problems occurred in the process of transferring data processing system from visual to optics. Therefore, it is appropriate to approach these problems in terms of optics. The results show that the optical visual cryptograph system has both the effectiveness and reliability as well as real-time implementation property.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.