Showing papers on "Visual cryptography published in 1997"

Constructions and Properties of k out of nVisual Secret Sharing Schemes

Abstract: The idea of visual k out of n secret sharing schemes was introduced in Naor. Explicit constructions for k = 2 and k = n can be found there. For general k out of n schemes bounds have been described. Here, two general k out of n constructions are presented. Their parameters are related to those of maximum size arcs or MDS codes. Further, results on the structure of k out of n schemes, such as bounds on their parameters, are obtained. Finally, the notion of coloured visual secret sharing schemes is introduced and a general construction is given.

Visual authentication and identification

Abstract: The problems of authentication and identification have received wide interest in cryptographic research. However, there has been no satisfactory solution for the problem of authentication by a human recipient who does not use any trusted computational device, which arises for example in the context of smartcard-human interaction, in particular in the context of electronic wallets. The problem of identification is ubiquitous in communication over insecure networks. This paper introduces visual authentication and visual identification methods, which are authentication and identification methods for human users based on visual cryptography. These methods are very natural and easy to use, and can be implemented using very common low tech technology. The methods we suggest are efficient in the sense that a single transparency can be used for several authentications or for several identifications. The security of these methods is rigorously analyzed.

Contrast-optimal k out of n secret sharing schemes in visual cryptography (extended abstract)

Abstract: Visual cryptography and (k,n)-visual secret sharing schemes were introduced by Naor and Shamir in [NaSh1]. A sender wishing to transmit a secret message distributes n transparencies among n recipients, where the transparencies contain seemingly random pictures. A (k, n)-scheme achieves the following situation: If any k recipients stack their transparencies together, then a secret message is revealed visually. On the other hand, if only k - 1 recipients stack their transparencies, or analyze them by any other means, they are not able to obtain any information about the secret message. The important measures of a scheme are its contrast, i.e., the clarity with which the message becomes visible, and the number of subpixels needed to encode one pixel of the original picture. Naor and Shamir constructed (k, k)-schemes with contrast 2 -(k-1) . By an intricate result from [LN2], they were also able to prove optimality. They also proved that for all fixed k ≤ n, there are (k, n)-schemes with contrast (2e)- k /√2πk -for k = 2, 3, 4 the contrast is approx. 1/105, 1/698 and 1/4380.) In this paper, we show that by solving a simple linear program, one is able to compute exactly the best contrast achievable in any (k,n)-scheme. The solution of the linear program also provides a representation of the corresponding scheme. For small k as well as for k = n, we are able to analytically solve the linear program. For k = 2,3,4, we obtain that the optimal contrast is at least 1/4,1/16 and 1/64. For k = n, we obtain a very simple proof of the optimality of Naor's and Shamir's (k,k)-schemes. In the case k = 2, we are able to use a different approach via coding theory which allows us to prove an optimal tradeoff between the contrast and the number of subpixels.

Contrast-Optimal k out of n Secret Sharing Schemes in Visual Cryptography

Abstract: Visual cryptography and (k, n)-visual secret sharing schemes were introduced by Naor and Shamir in [NaSh1] A sender wishing to transmit a secret message distributes n transparencies among n recipients, where the transparencies contain seemingly random pictures A (k, n)-scheme achieves the following situation: If any k recipients stack their transparencies together, then a secret message is revealed visually On the other hand, if only k - 1 recipients stack their transparencies, or analyze them by any other means, they are not able to obtain any information about the secret message

Traceable visual cryptography

Abstract: In this paper we present a new k out of n visual cryptography scheme which does not only meet the requirements of a basic visual cryptography scheme defined by Naor and Shamir [5] but is also traceable. A k out of n visual cryptography scheme is a special instance of a k out of n threshold secret sharing scheme [6]. Thus, no information about the original secret can be revealed if less than k share-holders combine their shares. In those systems it is inherently assumed that even if there are k or more share-holders with an interest in the abuse of the secret, then it is almost impossible that they can meet up as an entirety (e.g. because they are to cautious to inform too many others about their intentions) and combine their shares to misuse the secret. But in real scenarios it might not be too unlikely that the betrayers find together in small groups. Even though each one of these groups is too small to compute the original secret, the betrayers of such a group can impose a major security risk on the system by publishing the information about their shares. Suppose for example that k − 1 betrayers find each other and do the publishing. Then all the other n − k + 1 share-holders can potentially reveal the secret without ever meeting up with at least k − 1 other share-holders as is intended by the system. In order to cope with this lack of security, we present in this paper the idea of traceable visual cryptography schemes which allows to track down the publishing saboteurs.