Two Step Share Visual Cryptography Algorithm for Secure Visual Sharing

This paper re - examines the problem of visual secret sharing for general access structures by using visual cryptograms of random grids (VCRG). Given a binary or color secret image shared by a set of n participants with a strong access structure, we devise t wo effective algorithms to produce a set of VCRG so that the members in each qualified set can reconstruct the secret image by superimposing their sh ares, while those in any forbidden set cannot. The basic 2 out of 2 visual cryptography model consists of a secret message encoded into two transparencies, one transparency representing the cipher text and the other acting as a secret key. Both transparencies appear to be random dots when inspected individually and provide no information about the original clea r text. However, by carefully aligning the transparencies, the original secret message is reproduced. The actual decoding is accomplished by the human visual system. Our algorithms do not require any extr a pixel expansion, which is indispensable and grows exponentially as n increases in conventional visual cryptographic schemes

A Benchmarking assessment of known visual cryptography algorithms

With the growth of digital media, it is becoming more prevalent to find a method to protect the security of that media. An effective method for securely transmitting images is found in the field of Visual Cryptography. While this method is effective for securely transmitting images, many methods have been developed since the first algorithm was proposed in 1994 by Naor and Shamir. A benchmarking scheme is proposed to give the algorithm capabilities, understand the implementation method, evaluate the algorithm development, and provide image reconstruction information. Additionally, the algorithms are ranked according to a Visual Cryptography standard. This would allow an easy way to differentiate between algorithms and determine the ideal algorithm for a given task or project

CHARAKTERYSTYKA WYBRANYCH TECHNIK UKRYWANIA OBRAZU

Considering that different techniques of hiding images are known for a  long time, but have not found wider application, perhaps because of  their shortcomings. In this publication are described some types of techniques secret sharing images that are already in use. The author aims to review these techniques and  summarizes their features.Zważywszy, że różne techniki utajniania obrazów są znane od dawna, lecz nie znalazły szerszego zastosowania, być może ze względu na ich mankamenty, w tej publikacji zostaną opisane niektóre rodzaje technik sekretnego podziału obrazów, które już są. Autor ma na celu przeglądnięcie tych technik i ich podsumowanie

Secure two-party computation: a visual way

In this paper we propose a novel method for performing secure two-party computation. By merging together in a suitable way two beautiful ideas of the 80\u27s and the 90\u27s, Yao\u27s garbled circuit construction and Naor and Shamir\u27s visual cryptography, respectively, we enable Alice and Bob to securely evaluate a function $f(\cdot,\cdot)$ of their inputs, $x$ and $y$, through a {\em pure physical} process. Indeed, once Alice has prepared a set of properly constructed transparencies, Bob computes the function value $f(x,y)$ by applying a sequence of simple steps which require the use of a pair of scissors, superposing transparencies, and the human visual system. A crypto-device for the function evaluation process is not needed any more

Bounded Indistinguishability and the Complexity of Recovering Secrets

Motivated by cryptographic applications, we study the notion of {\em bounded indistinguishability}, a natural relaxation of the well studied notion of bounded independence. We say that two distributions $\mu$ and $\nu$ over $\Sigma^n$ are {\em $k$-wise indistinguishable} if their projections to any $k$ symbols are identical. We say that a function f\colon \Sigma^n \to \zo is {\em \e-fooled by $k$-wise indistinguishability} if $f$ cannot distinguish with advantage \e between any two $k$-wise indistinguishable distributions $\mu$ and $\nu$ over $\Sigma^n$. We are interested in characterizing the class of functions that are fooled by $k$-wise indistinguishability. While the case of $k$-wise independence (corresponding to one of the distributions being uniform) is fairly well understood, the more general case remained unexplored. When \Sigma = \zo, we observe that whether $f$ is fooled is closely related to its approximate degree. For larger alphabets $\Sigma$, we obtain several positive and negative results. Our results imply the first efficient secret sharing schemes with a high secrecy threshold in which the secret can be reconstructed in AC$^0$. More concretely, we show that for every $0 < \sigma < \rho \leq 1$ it is possible to share a secret among $n$ parties so that any set of fewer than $\sigma n$ parties can learn nothing about the secret, any set of at least $\rho n$ parties can reconstruct the secret, and where both the sharing and the reconstruction are done by constant-depth circuits of size \poly(n). We present additional cryptographic applications of our results to low-complexity secret sharing, visual secret sharing, leakage-resilient cryptography, and protecting against ``selective failure\u27\u27 attacks

Probabilistic visual cryptography schemes

Visual cryptography schemes allow the encoding of a secret image, consisting of black or white pixels, into n shares which are distributed to the participants. The shares are such that only qualified subsets of participants can ‘visually ’ recover the secret image. The secret pixels are shared with techniques that subdivide each secret pixel into a certain number m, m ≥ 2 of subpixels. Such a parameter m is called pixel expansion. Recently Yang introduced a probabilistic model. In such a model the pixel expansion m is 1, that is, there is no pixel expansion. The reconstruction of the image however is probabilistic, meaning that a secret pixel will be correctly reconstructed only with a certain probability. In this paper we propose a generalization of the model proposed by Yang. In our model we fix the pixel expansion m ≥ 1 that can be tolerated and we consider probabilistic schemes attaining such a pixel expansion. For m = 1 our model reduces to the one of Yang. For big enough values of m, for which a deterministic scheme exists, our model reduces to the classical deterministic model. We show that between these two extremes one can trade the probability factor of the scheme with the pixel expansion. Moreover, we prove that there is a one-to-one mapping between deterministic schemes and probabilistic schemes with no pixel expansion, where contrast is traded for the probability factor. 1

Probabilistic Visual Cryptography Schemes

Visual cryptography schemes allow the encoding of a secret image, consisting of black or white pixels, into n shares that are distributed to the set P of n participants. The shares are such that only qualified subsets of participants can \u201cvisually\u201d recover the secret image. The secret pixels are shared with techniques based on subdividing each secret pixel into a certain number m, m = 2 of subpixels. Such a parameter m is called the pixel expansion, since the reconstructed shared image becomes m times bigger than the original. This cryptographic paradigm was introduced by Naor and Shamir [16]. They analyzed the case of (k, n)-threshold visual cryptography schemes, in which a black and white secret image is visible if and only if any k transparencies are stacked together

Probabilistic Visual Cryptography Schemes

Visual cryptography schemes allow the encoding of a secret image, consisting of black or white pixels, into n shares which are distributed to the participants. The shares are such that only qualified subsets of participants can ``visually'' recover the secret image. The secret pixels are shared with techniques that subdivide each secret pixel into a certain number m, m>= 2 of subpixels. Such a parameter $m$ is called the pixel expansion. Recently Yang introduced a probabilistic model. In such a model the pixel expansion m is 1, that is, there is no pixel expansion. The reconstruction of the image however is probabilistic, meaning that a secret pixel will be correctly reconstructed only with a certain probability. In this paper we propose a generalization of the model proposed by Yang. In our model we fix the pixel expansion m >= 1 that we can tolerate and we consider probabilistic schemes attaining such a pixel expansion. For m=1 our model reduces to the one of Yang. For big enough values of m, for which a deterministic scheme exists, our model reduces to the classical deterministic model. We show that between these two extremes one can trade the probability factor of the scheme with the pixel expansion. Moreover we prove that there is a one-to-one mapping between deterministic schemes and probabilistic schemes with no pixel expansion, where the contrast is traded for the probability factor