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306
An InformationTheoretic Model for Steganography
, 1998
"... An informationtheoretic model for steganography with passive adversaries is proposed. The adversary's task of distinguishing between an innocentcover message C and a modified message S containing a secret part is interpreted as a hypothesis testing problem. The security of a steganographic sys ..."
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Cited by 267 (3 self)
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An informationtheoretic model for steganography with passive adversaries is proposed. The adversary's task of distinguishing between an innocentcover message C and a modified message S containing a secret part is interpreted as a hypothesis testing problem. The security of a steganographic system is quantified in terms of the relative entropy (or discrimination) between PC and PS . Several secure steganographic schemes are presented in this model; one of them is a universal information hiding scheme based on universal data compression techniques that requires no knowledge of the covertext statistics.
Visual Cryptography for General Access Structures
, 1996
"... A visual cryptography scheme for a set P of n participants is a method to encode a secret image SI into n shadow images called shares, where each participant in P receives one share. Certain qualified subsets of participants can "visually" recover the secret image, but other, forbidden, se ..."
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Cited by 103 (9 self)
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A visual cryptography scheme for a set P of n participants is a method to encode a secret image SI into n shadow images called shares, where each participant in P receives one share. Certain qualified subsets of participants can "visually" recover the secret image, but other, forbidden, sets of participants have no information (in an informationtheoretic sense) on SI . A "visual" recovery for a set X ` P consists of xeroxing the shares given to the participants in X onto transparencies, and then stacking them. The participants in a qualified set X will be able to see the secret image without any knowledge of Cryptography and without performing any cryptographic computation. In this paper we propose two techniques to construct visual cryptography schemes for general access structures. We analyze the structure of visual cryptography schemes and we prove bounds on the size of the shares distributed to the participants in the scheme. We provide a novel technique to realize k out of n thre...
Visual Authentication and Identification
 Lecture Notes in Computer Science
"... 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. The problem of authentication arises for ..."
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Cited by 61 (1 self)
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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. The problem of authentication arises for example in the context of smartcardhuman 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 visual authentication methods we suggest are not limited to auth...
ReceiptFree UniversallyVerifiable Voting with Everlasting Privacy
 In CRYPTO
, 2006
"... Abstract. We present the first universally verifiable voting scheme that can be based on a general assumption (existence of a noninteractive commitment scheme). Our scheme is also the first receiptfree scheme to give “everlasting privacy ” for votes: even a computationally unbounded party does not ..."
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Cited by 49 (3 self)
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Abstract. We present the first universally verifiable voting scheme that can be based on a general assumption (existence of a noninteractive commitment scheme). Our scheme is also the first receiptfree scheme to give “everlasting privacy ” for votes: even a computationally unbounded party does not gain any information about individual votes (other than what can be inferred from the final tally). Our voting protocols are designed to be used in a “traditional ” setting, in which voters cast their ballots in a private polling booth (which we model as an untappable channel between the voter and the tallying authority). Following in the footsteps of Chaum and Neff [7, 16], our protocol ensures that the integrity of an election cannot be compromised even if the computers running it are all corrupt (although ballot secrecy may be violated in this case). We give a generic voting protocol which we prove to be secure in the Universal Composability model, given that the underlying commitment is universally composable. We also propose a concrete implementation, based on the hardness of discrete log, that is more efficient. 1.
On the Contrast in Visual Cryptography Schemes
 Journal of Cryptology
, 1999
"... 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 ..."
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Cited by 48 (3 self)
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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 onetoone mapping between deterministic schemes and probabilistic schemes with no pixel expansion, where contrast is traded for the probability factor. 1.
Three Voting Protocols: ThreeBallot, VAV, and Twin
 Proceedings of USENIX/ACCURATE Electronic Voting Technology (EVT
, 2007
"... We present three new paperbased voting methods with interesting security properties. Our goal is to achieve the same security properties as recently proposed cryptographic voting protocols, but using only paper ballots and no cryptography. From a security viewpoint we get reasonably close, particul ..."
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Cited by 42 (0 self)
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We present three new paperbased voting methods with interesting security properties. Our goal is to achieve the same security properties as recently proposed cryptographic voting protocols, but using only paper ballots and no cryptography. From a security viewpoint we get reasonably close, particularly for short ballots. However, our proposals should probably be considered as more “academic ” than “practical.” In these proposals, not only can each voter verify that her vote is recorded as intended, but she gets a “receipt ” she can take home that can be used later to verify that her vote is actually included in the final tally. But her receipt does not allow her to prove to anyone else how she voted. All ballots cast are scanned and published in plaintext on a “public bulletin board ” (web site), so anyone may correctly compute the election result. In ThreeBallot, each voter casts three paper ballots, with certain restrictions on how they may be filled out. These paper ballots are of course “voterverifiable.” A voter receives a copy of one of her ballots as her “receipt”, which she may take home. Only the voter knows which ballot she copied for her receipt. The voter is unable to use her receipt to prove how she voted or to sell her vote, as the receipt doesn’t reveal how she voted. A voter can check that the web site contains a ballot matching her receipt. Deletion or modification of ballots is thus detectable; so the integrity of the election is verifiable. VAV is like ThreeBallot, except that the ballotmarking rules are different: one ballot may “cancel” another (VAV = Vote/AntiVote/Vote). VAV is better suited to – i.e. yields better security properties ∗ The latest version of this paper is always at
Visual Cryptography for Graylevel Images by Dithering Techniques
 Pattern Recognition Letters 24 (2003) 349358. ELSEVIER. Available at Computer Science Web, powered by SCIENCE DIRECT. http://www.cis.nctu.edu.tw/~whtsai/Journal%20Paper%2 0PDFs/Lin_&_Tsai_PRL_2003.pdf
, 2003
"... A ðk; nÞthreshold visual cryptography scheme is proposed to encode a secret image into n shadow images, where any k or more of them can visually recover the secret image, but any k 1 or fewer of them gain no information about it. The decoding process of a visual cryptography scheme, which differs ..."
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Cited by 39 (0 self)
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A ðk; nÞthreshold visual cryptography scheme is proposed to encode a secret image into n shadow images, where any k or more of them can visually recover the secret image, but any k 1 or fewer of them gain no information about it. The decoding process of a visual cryptography scheme, which differs from traditional secret sharing, does not need complicated cryptographic mechanisms and computations. Instead, it can be decoded directly by the human visual system. Previous efforts in this topic are almost restricted in processing binary images, which are insufficient for many applications. In this paper, a new visual cryptography scheme suitable for graylevel images is proposed. Instead of using gray subpixels directly to construct shares, a dithering technique is used first to convert a graylevel image into an approximate binary image. Then existing visual cryptography schemes for binary images are applied to accomplish the work of creating shares. The overall effect of the proposed method is the achievement of visual encryption and decryption functions for graylevel images. Some comparisons with a previously proposed method are also made. Some experimental results are shown to prove the feasibility of the proposed method. Finally, an application is mentioned to show its practicability.
Applications of Combinatorial Designs to Communications, Cryptography, and Networking
, 1999
"... ... In this paper, we focus on another collection of recent applications in the general area of communications, including cryptography and networking. Applications have been chosen to represent those in which design theory plays a useful, and sometimes central, role. Moreover, applications have been ..."
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Cited by 37 (3 self)
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... In this paper, we focus on another collection of recent applications in the general area of communications, including cryptography and networking. Applications have been chosen to represent those in which design theory plays a useful, and sometimes central, role. Moreover, applications have been chosen to reflect in addition the genesis of new and interesting problems in design theory in order to treat the practical concerns. Of many candidates, thirteen applications areas have been included. They are as follows:
Prêt à voter: a systems perspective
, 2005
"... Numerous cryptographic voting schemes have been proposed in recent years. Many of these have highly desirable formal security properties. However, as with all security systems, even a welldesigned technical system can be undermined by implementation details or environmental factors, typically inclu ..."
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Cited by 35 (12 self)
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Numerous cryptographic voting schemes have been proposed in recent years. Many of these have highly desirable formal security properties. However, as with all security systems, even a welldesigned technical system can be undermined by implementation details or environmental factors, typically including human users, that violate (often implicit) assumptions of the design and evaluation. In ‘Cryptographic Voting Protocols: a System Perspective ’ [11] Karlof et al perform a systemsbased analysis of the Chaum [5] and Neff [17], [18], [19] schemes. They identify a number of vulnerabilities and discuss possible mitigations and countermeasures. In this paper, we examine the extent to which these vulnerabilities carry over to the Prêt à Voter scheme [6]. In addition, we describe some further systemsbased vulnerabilities not identified in [11]. We also discuss some further threats, such as chain voting attacks, which do not apply to the Chaum or Neff schemes but to which Prêt à Voter is vulnerable, unless appropriate countermeasures are deployed. It turns out that Prêt à Voter is remarkably robust to most of the vulnerabilities described in [11] and here. 1