Showing papers on "Visual cryptography published in 1998"

Audio and Optical Cryptography

Abstract: In visual cryptography the additive property of light is used Also the shares are random and therefore suspect to a censor In this paper we present two new cryptographic schemes which use music and the wave properties of light Both schemes are also secret sharing schemes in which shares are music or images and are not suspect to a human censor Our scheme guarantees perfect privacy as well as high quality To decrypt the message, one just plays two shares on a stereo system There are two decryption methods which are either based on the interference property of sound or based on the stereo perception of the human hearing system In optical cryptography, we use pictures as covers and the wave interference property of light The privacy is perfect and the modified images are non-suspicious The Mach-Zehnder interferometer is used as the decryption machine

On Construction of Cumulative Secret Sharing Schemes

Abstract: Secret sharing schemes are one of the most important primitives in distributed systems. Cumulative secret sharing schemes provide a method to share a secret among a number of participants with arbitrary access structures.

On visual cryptography schemes

Abstract: We consider visual cryptography schemes in which two pixels combine in an arbitrary way. We analyze the pixel expansion and the contrast of (2,n)-threshold visual cryptography schemes, that is schemes in which any pair of n shares can visually reconstruct the secret image, but any single share has no information on the secret image.

Linear threshold schemes, visual cryptography, and parasite-host cryptosystems

Abstract: This dissertation consists of three parts. The first part is a study of Blakley's vector threshold scheme (BVTS) and a generalization of it to linear threshold schemes (LTS). This first part generalizes the BVTS, shows that Shamir's threshold scheme (STS) is a special case of the BVTS, and shows that the generalized BVTS is Shannon perfectly secure. It shows that the STS can be modified so as to increase the number of its participants by at least one, and also studies the relationship between rigid and nonrigid BVTS. The second part, a study of visual cryptography schemes (VCS), proposes a new method for constructing uniform visual threshold schemes (VTS) in such a way that the constructor can exercise control over the above-threshold behavior of the scheme. It presents fast algorithms for constructing such VTS, and introduces two new notions in VTS, verifier and wild card. It presents fast algorithms for constructing VTS with verification and VTS with wild card. It also combines VTS and ramp schemes to produce the concept of Generalized Visual Threshold Scheme (GVTS), which exhibits Shannon relative security. The third part extends the ideas of subliminal channels and kleptography and introduces parasite-host cryptosystems (PHC). A PHC consists of a host cryptosystem, as well as a parasite cryptosystem resident within the host cryptosystem. The host cryptosystem works in the ordinary manner. The (legitimate) users of the host cryptosystem can decrypt (verify, recover) the output of the PHC. The parasite cryptosystem relies on the output of the host cryptosystem. However, the (ab)users, who hold the keys peculiar to the parasite cryptosystem, can decrypt (verify, recover) an additional parasite output implicit in the aforementioned output of the host cryptosystem. This third part of the dissertation also defines three kinds of security with respect to the parasite cryptosystem belonging to a given PHC. They are called plain, computational, and perfect security. It presents several constructions of PHC related to threshold schemes.

Visual Cryptography — How to Use Images to Share a Secret

Abstract: In this paper, we give a survey of visual cryptography schemes, a new type of cryptographic schemes which was first introduced by Naor and Shamir [9] in 1994. Visual cryptography schemes can be considered as encryption schemes based on graphical data. In visual cryptography schemes as special instances of secret sharing schemes, the secret information is encoded by the construction of several fragments, called shares which are distributed secretly to different, not necessarily trustworthy parties. In order to reconstruct the secret image, a qualified subset of these parties has to combine their shares. For example, in (K, n)—threshold schemes there are n different parties and each subset of at least k parties is qualified. Visual cryptography schemes are perfect, i.e., forbidden (i.e., not qualified) subsets of parties learn no information at all about the encrypted image (in the information-theoretic sense). In contrast to conventional encryption (resp. secret sharing) schemes, visual cryptography schemes allow the decryption to be done directly by the human visual system, i.e., without performing any sophisticated cryptographic computations.

How to Use Images to Share a Secret

Abstract: In this paper, we give a survey of visual cryptography schemes, a new type of cryptographic schemes which was first intro­ duced by Naor and Shamir (9) in 1994. Visual cryptography schemes can be considered as encryption schemes based on graphical data. In visual cryptography schemes as special instances of secret sharing schemes, the secret information is encoded by the construction of several frag­ ments, called shares which are distributed secretly to different, not nec­ essarily trustworthy parties. In order to reconstruct the secret image, a qualified subset of these parties has to combine their shares. For example, in (k, n)-threshold schemes there are n different parties and each subset of at least k parties is qualified. Visual cryptography schemes are perfect, Le., forbidden (Le., not qualified) subsets of parties learn no information at all about the encrypted image (in the information-theoretic sense). In contrast to conventional encryption (resp. secret sharing) schemes, visual cryptography schemes allow the decryption to be done directly by the human visual system, Le., without performing any sophisticated cryptographic computations.