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Dissertations / Theses on the topic 'Visual cryptography'
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1
Muecke, Innes. "Greyscale and colour visual cryptography." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0017/MQ48283.pdf.
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Weir, J. P. "Visual cryptography and its applications." Thesis, Queen's University Belfast, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.557852.
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" In this thesis, a number of new schemes are presented which address current problems and shortcomings within the area of visual cryptography. Visual cryptography provides a very powerful means by which a secret, in the form of a digital image, can be distributed (encoded) into two or more pieces known as shares. When these shares are xeroxed onto transparencies and superimposed exactly together, the original secret can be recovered (decoded) without the necessity for computation. Traditionally, visual cryptography allows effective and efficient sharing of a single secret between a number of trusted parties. One aspect of the research within this thesis specifically addresses the issues of embedding more than two secrets within a set of two shares. Alignment poses a further problem. The placement of the shares must be specific. In order to ease ali~ent, the techniques developed within this thesis for sharing multiple secrets relaxes this restriction. The result is a scheme in which the shares can be superimposed upon one another in a multitude of positions and alignment styles which enables multiple secret recovery. Applications of visual cryptography are also examined and presented. This is an area within visual cryptography that has had very little attention in terms of research. The primary focus of the work presented within this thesis concentrates on applications of visual cryptography in real world scenarios. For such a simple and effective method of sharing secrets, practical applications are as yet, limited. A number of novel uses for visual cryptography are presented that use theoretical techniques in a practical way.
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Islam, Naveed. "Cryptography based Visual Data Protection." Thesis, Montpellier 2, 2011. http://www.theses.fr/2011MON20178/document.
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La transmission de données multimédia sur les réseaux sécurisés a une croissance exponentielle grâce aux progrès scientifique dans les technologies de l'information et de la communication. La sécurité des données dans certaines applications comme le stockage sécurisé, l'authentification, la protection des droits d'auteurs, la communication militaire ou la visioconférence confidentielles, nécessitent de nouvelles stratégies en matière de transmission sécurisée. Deux techniques sont couramment utilisées pour la transmission sécurisée de données visuelles, à savoir : la cryptographie et la stéganographie. La cryptographie sécurise les données en utilisant des clés secrètes afin de rendre les données illisibles, la stéganographie, elle, vise à insérer des données cruciales dans des signaux porteurs anodins.De plus, pour la confiance mutuelle et les systèmes distribués, le partage sécurisé de ressources est souvent une garantie suffisante pour les applications de communication. L'objectif principal de cette thèse est de réaliser une protection des données visuelles, en particulier les images numériques, par le biais des techniques modernes de cryptographie. Dans ce contexte, deux objectifs de recherche ont été développés durant ces travaux de thèse.La première partie de notre travail se concentre sur la sécurité des images numériques dans un environnement partagé. Ensuite, la deuxième partie porte sur l'intégrité des données visuelles pendant une transmission sécurisée.Nous avons proposé un nouveau schéma de partage des images qui exploite les propriétés d'addition et de multiplication homomorphique de deux crypto systèmes à clé publique largement utilisés : les algorithmes RSA et Paillier. Dans les schémas traditionnels de partage sécurisé, le ``dealer'' partitionne le secret en parties et le distribue à chacun des autres acteurs. Ainsi, aucun des acteurs impliqués ne participe à la création du partage sécurisé, mais il est toujours possible que le ``dealer'' transmette des données malveillantes. Au contraire, l'approche proposée utilise le système de partage de secret d'une manière qui limite l'influence du ‘‘dealer'' sur le protocole en permettant à chaque acteur de participer.La deuxième partie de ces travaux de thèse met l'accent sur l'intégrité des données visuelles lors de la transmission. L'intégrité des données signifie que les données gardent leurs structures complètes au cours d'une opération numérique comme le stockage, le transfert ou la récupération. Le changement d'un seul bit de données cryptées peut avoir un impact catastrophique sur les données décryptées. Nous abordons le problème de correction d'erreurs dans les images cryptées en utilisant le chiffrement à clé symétrique AES (Advanced Encryptions Standard) suivant différents modes. Trois mesures sont proposées afin d'exploiter les statistiques locales des données visuelles et l'algorithme de chiffrement, dans l'objectif de corriger les erreurs efficacementDue to the advancements in the information and communication technologies, the transmission of multimedia data over secure or insecure communication channels has increased exponentially. The security of data in applications like safe storage, authentications, copyright protection,remote military image communication or confidential video-conferencing require new strategies for secure transmission. Two techniques are commonly used for the secure transmission of visual data, i.e. cryptography and steganography. Cryptography achieves security by using secret keysto make the data illegible while steganography aims to hide the data in some innocent carrier signal. For shared trust and distributed environment, secret sharing schemes provide sufficient security in various communication applications. The principal objective of this thesis is to achieveprotection of visual data especially images through modern cryptographic techniques. In this context, the focus of the work in perspective, is twofolded. The first part of our work focuses on the security of image data in shared environment while the second part focuses on the integrity ofimage data in the encrypted domain during transmission.We proposed a new sharing scheme for images which exploits the additive and multiplicative homomorphic properties of two well known public key cryptosystems, namely, the RSA and the Paillier. In traditional secret sharing schemes, the dealer partitions the secret into shares and distributethe shares to each of the player. Thus, none of the involved players participate in the creation of the shared secret and there is always a possibilitythat the dealer can cheat some player. On the contrary, the proposed approach employs the secret sharing scheme in a way that limits the influence of the dealer over the protocol by allowing each player to participate. The second part of our thesis emphasizes on the integrity of visual data during transmission. Data integrity means that the data have its complete structure during any operation like storage, transfer or retrieval. A single bit change in encrypted data can have catastrophic impact over the decrypted data. We address the problem of error correction in images encrypted using symmetric key cryptosystem of the Advanced Encryption Standard (AES) algorithm. Three methods are proposed to exploit the local statistics of the visual data and the encryption algorithm to successfully correct the errors
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Ghiotto, Nicolo' <1994>. "Visual Cryptography Schemes with Multiple Secrets and Visual Key Derivation." Master's Degree Thesis, Università Ca' Foscari Venezia, 2018. http://hdl.handle.net/10579/13323.
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Visual Cryptography was introduced in 1995 by Naor and Shamir to recover a secret image by overlapping two or more images. This scheme is secure and easy to implement and can be extended to a set of participants in order to recover the same secret image. In this thesis, we propose two new schemes that use a shared image to encode a different secret image for each participant. In the first scheme, we generate a visual cyphertext from a shared key for each participant. Since the shared key is computed a priori, we can add a new participant at any given time and generate her cyphertext, ensuring scalability. In the second scheme, we make the approach more practical by applying a visual key derivation function in order to let each participant derive her visual cyphertext from a different password for each participant. This is a joint work with colleague Tommaso Moretto, who has developed implementations and performed practical experiments on these new schemes applied to barcode confidentially.
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Moretto, Tommaso <1992>. "Secure 2D barcodes based on visual cryptography." Master's Degree Thesis, Università Ca' Foscari Venezia, 2018. http://hdl.handle.net/10579/13391.
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In this thesis we investigate the application of visual cryptography to enforce 2D barcode confidentiality. The approach of visual cryptography is appealing because 2D barcodes are indeed images, but it presents non-trivial challenges. First of all, visual cryptography aims at sharing a unique secret between two or more participants while here we would like to provide each participant with a visual decryption key that can be used to recover the participant's distinguished secret; moreover, visual cryptography assumes that images are pre-shared among participants which is not practical in many situations. We contribute to the state-of-the-art by implementing and experimenting with two extensions to visual cryptography proposed together with the colleague Nicolò Ghiotto. The first scheme allows for generating a single visual ciphertext that can be decrypted by each participant’s visual key, giving a different (plaintext) 2D barcode. This scheme presents a practical limitation: the visual key is a random image that is very hard to scan and needs to be pre-shared. The second scheme extends the first one by permitting to derive the visual key from a password using what we call a visual key derivation function. This removes the limitation of the first scheme but introduces a scalability issue for what concerns the number of participants. We present experiments and discuss limitations with respect to real use cases.
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MacPherson, Lesley. "Grey Level Visual Cryptography for General Access Structures." Thesis, University of Waterloo, 2002. http://hdl.handle.net/10012/1126.
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Visual cryptography, first introduced by Naor and Shamir, allows a secret (black and white) image to be encoded and distributed to a set of participants such that certain predefined sets of participants may reconstruct the image without any computation. In 2000, Blundo, De Santis, and Naor introduced a model for grey-level visual cryptography which is a generalization of visual cryptography for general access structures. Grey-level visual cryptography extends this model to include grey-scale images. Decoding is done by the human visual system. In this thesis we survey known results of grey-level visual cryptography and visual cryptography for general access structures. We extend several visual cryptography constructions to grey-level visual cryptography, and derive new results on the minimum possible pixel expansion for all possible access structures on at most four participants.
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Koshta, Prashant Kumar, and Shailendra Singh Thakur. "A Novel Authenticity of an Image Using Visual Cryptography." IJCSN, 2012. http://hdl.handle.net/10150/219514.
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Information security in the present era is becoming very
important in communication and data storage. Data
transferred from one party to another over an insecure
channel (e.g., Internet) can be protected by cryptography.
The encrypting technologies of traditional and modern
cryptography are usually used to avoid the message from
being disclosed. Public-key cryptography usually uses
complex mathematical computations to scramble the
message.A digital signature is an important public-key primitive that performs the function of conventional handwritten signatures for entity authentication, data integrity, and non-repudiation, especially within the electronic commerce environment. Currently, most conventional digital signature schemes are based on mathematical hard problems. These mathematical algorithms require computers to perform the heavy and complex computations to generate and verify the keys and signatures. In 1995, Naor and Shamir proposed a visual cryptography (VC) for binary images. VC has high security and requires simple computations. The purpose of this thesis is to provide an alternative to the current digital signature technology. We introduce a new digital signature scheme based on the concept of a non-expansion visual cryptography. A visual digital signature scheme is a method to enable visual verification of the authenticity of an image in an insecure environment without the need to perform any complex computations. We proposed scheme generates visual shares and manipulates them using the simple Boolean operations OR rather than generating and computing large and long random integer values as in the conventional digital signature schemes currently in use.
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Maheshwari, Varun. "Data confidentiality and keyword search in the cloud using visual cryptography." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=106553.
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Security has emerged as the most feared aspect of cloud computing and a major hindrance for the customers. Current cloud framework does not allow encrypted data to be stored due to the absence of efficient searchable encryption schemes that allow query execution on a cloud database. Storing unencrypted data exposes the data not only to an external attacker but also to the cloud provider itself. Thus, trusting a provider with confidential data is highly risky. To enable querying on a cloud database without compromising data confidentiality, we propose to use data obfuscation through visual cryptography. A new scheme for visual cryptography is developed and configured for the cloud for storing and retrieving textual data. Testing the system with query execution on a cloud database indicates full accuracy in record retrievals with negligible false positives. In addition, the system is resilient to attacks from within and outside the cloud. Since standard encryption and key management are avoided, our approach is computationally efficient and data confidentiality is maintained.La sécurité a émergé comme l'aspect le plus redouté de l'informatique en nuage et comme un obstacle majeur pour les clients. Le cadre actuel de l'informatique en nuage ne permet pas que les données chiffrées soient stockées en raison de l'absence de schémas efficaces de cryptage qui permettent l'exécution des requêtes sur une base de données des nuages. Le stockage des données non cryptées expose les données non seulement à un agresseur extérieur, mais aussi au fournisseur de nuage lui-même. Ainsi, faire confiance à un fournisseur avec des données confidentielles est très risqué.Afin de permettre des requêtes sur une base de données des nuages sans compromettre la confidentialité des données, nous proposons d'utiliser l'obscurcissement des données à travers la cryptographie visuelle. Un nouveau schéma pour la cryptographie visuelle est développé et configuré pour le nuage pour stocker et récupérer des données textuelles. Tester le système avec l'exécution des requêtes sur une base de données nuée indique une grande précision dans la récupération des enregistrements avec négligeables faux positifs. En outre, le système est résistant aux attaques de l'intérieur et l'extérieur du nuage. Parce que le cryptage standard et la gestion des clés sont évités, notre approche est mathématiquement efficace et la confidentialité des données est assurée.
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Leung, Wing Pan. "Visual cryptography for color images : formal security analysis and new construction /." access full-text access abstract and table of contents, 2009. http://libweb.cityu.edu.hk/cgi-bin/ezdb/thesis.pl?mphil-cs-b23759100f.pdf.
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Thesis (M.Phil.)--City University of Hong Kong, 2009."Submitted to Department of Computer Science in partial fulfillment of the requirements for the degree of Master of Philosophy." Includes bibliographical references (leaves 103-108)
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Potay, Sunny. "Efficient algorithm to construct phi function in vector space secret sharing scheme and application of secret sharing scheme in Visual Cryptography." TopSCHOLAR®, 2012. http://digitalcommons.wku.edu/theses/1151.
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Secret Sharing refers to a method through which a secret key K can be shared among a group of authorized participants, such that when they come together later, they can figure out the secret key K to decrypt the encrypted message. Any group which is not authorized cannot determine the secret key K. Some of the important secret schemes are Shamir Threshold Scheme, Monotone Circuit Scheme, and Brickell Vector Space Scheme. Brikell’s vector space secret sharing construction requires the existence of a function from a set of participant P in to vector space Zdp, where p is a prime number and d is a positive number. There is no known algorithm to construct such a function in general. We developed an efficient algorithm to construct function for some special secret sharing scheme. We also give an algorithm to demonstrate how a secret sharing scheme can be used in visual cryptography.
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Machizaud, Jacques. "Cryptographie visuelle pour l’authentification de documents." Thesis, Saint-Etienne, 2012. http://www.theses.fr/2012STET4010/document.
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La cryptographie visuelle consiste à partager entre plusieurs « Shadow Images » (SIs) un secret qui ne se révèlera à l'oeil de l'observateur qu'à leur superposition. Depuis les travaux de Naor et Shamir, ce procédé cryptographique a été étendu à Des schémas numériques variés, adaptés à diverses problématiques. En revanche, les travaux concernant son implémentation physique sont peu nombreux à ce jour. Cette thèse est consacrée à l'implémentation de la cryptographie visuelle sur des SIs imprimés en demi-tons en vue de l'authentification de documents. Le SI associé au document peut être imprimé sur support opaque ou transparent, les autres SIs étant imprimés sur films transparents. Nous avons résolu la difficulté de leur superposition par une méthode de Fourier permettant le recalage de la structure quasi-périodique d'un SI. La précision de cette méthode nous a permis de développer un système optique de superposition par projection. On verra que les phénomènes physiques responsables du rendu visuel de SIs superposés sont propices à une protection contre la copie illicite du SI associé à un document. La complexité de ces phénomènes et leur dépendance au type d'impression imposent une modélisation physique pour obtenir un rendu précis. Cette approche nous a conduit à considérer la problématique de la reproduction des couleurs et à développer des modèles spectraux adaptés à la superposition de supports imprimés non diffusants et/ou diffusants, en réflexion et en transmission. La précision de ces modèles prédictifs est tout à fait satisfaisante au regard de celle habituellement obtenue dans le domaine de la reproduction des couleurs. Cela nous a permis d'introduire une approche originale de la cryptographie visuelle par ajustement de couleur (color matching) : une même couleur, à une tolérance près basée sur la vision humaine, est générée par différents demi-tons imprimés sur les supports à superposer. La couleur du message peut ainsi constituer un secret partagé entre les SIs de la même façon que l'est le contenu du message. Chaque SI pris individuellement ne laisse fuir aucune information sur la couleur du message, qui ne sera révélée qu'à leur superposition. Cela peut permettre de prévenir une attaque par falsification du SI associé au document (cheating attack ). De plus, le rendu des couleurs étant très dépendant du système d'impression utilisé, une reproduction fidèle à partir d'un système d'impression différent est difficile. La difficulté peut être encore accrue par l'utilisation de caractéristiques d'impression non standardIn this thesis, we will focus on the physical implementation of visual cryptography, which consists in sharing a secret message between several unmeaning images, so-called shadow images, at least one of them being printed. By the principle of the method, no information leaks about the message until the images are properly stacked together. As the alignment of the shadow images hampers the deployment of the visual cryptography in practice, we develop a dedicated image registration method. In contrast with existing methods, ours is not intrusive. We make use of the particular shape of the elementary constituents of the shadow images, the shares, to extract in the Fourier domain the main parameters of the geometrical transformations occurring between the superposed images. We prove that this method allows subpixel accuracy in shadow images registration. We benefit from such ability by implementing visual cryptography in an image projection configuration : the digital shadow image is projected onto the printed one. In this way, the registration is performed automatically by using a digital camera (the resulting superposition being observable by the eye). For the purpose of authentication, one has to deal with specific attacks: the shadow image attached to a given document could be tampered with or copied. In order to prevent such attacks, we have increased the di_culty to reproduce the shadow image by considering color. This approach requires a complete management of colors. Thanks to recent advances in color reproduction, we are able to predict the reflectance and transmittance spectra of supports printed in color. In this thesis, we develop new spectral prediction models namely for piles of printed transparencies as well as for transparencies stacked onto papers, all printed in color. Thus, we are able to predict the color of each share in a shadow image to be printed and to achieve color matching i.e. we are able to reach a color by various combinations of superposed colors. Such a prediction allowed us to introduce a new approach in visual cryptography: color matching when revealing the secret message to be shared into two (or more) shadow images, in order to authenticate the shadow images provider. As the prediction models are sensitive to the calibration of the printing system (printer, inks, supports, halftoning and geometry measurement conditions), the use of special materials will increase the di_culty to generate visually acceptable fake pairs of shadow images
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Chen, Li-Ling, and 陳俐伶. "Visual Cryptography Using Meaningful Shares." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/99246307588438877666.
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碩士大同大學
通訊工程研究所
95
Visual cryptography (VC) has been developed as an efficient image encryption method. In the thesis, we proposed a new visual cryptography algorithm to achieve non-pixel expansion VC using meaningful shares. To maintain the visibility of object in shares and secret image, we use four parameters PSHb, PSHw, PSIb and PSIw to set the contrast in the share images and the decrypted image. Also, we use different block sizes to control the brightness and quality of shares and decrypted image. The schemes of (2, 2), (2, n) and (n, n) are developed and experimental results shows the effectiveness of our visual cryptography algorithm.
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Ciou, Yi-Sian, and 邱益賢. "An Improved Color Visual Cryptography." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/nfw963.
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碩士健行科技大學
資訊工程系碩士班
102
With the rapid development of social technology and widely used Internet, in order to ensure the security of Internet and to prevent others from illegal copying, destruction, and modification, steganography, visual cryptography and many other approaches are then developed. Visual cryptography provides a practical method, however, the use of visual cryptography was originally confined to black and white images. The follow-up studies extended visual cryptography to grayscale and color images. This study proposes a new method which combined a new codebook with random grid method in color visual cryptography. According to the experimental results, the color images can be used to hide information. As a result, it ensures security in terms of reduction of secret image. Compared with others, our method could be better than previous approaches in some scenarios, and the proposed method also solves the traditional problem of pixel expansion of visual cryptography.
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CHEN, YI-BIN, and 陳毅賓. "Studies on Tagged Visual Cryptography." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/9q7n5f.
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碩士銘傳大學
資訊工程學系碩士班
104
The appearance of shares encoded by the traditional visual cryptography is meaningless, and it is not friendly and difficult to distinguish and manage. Tagged visual cryptography (TVC) embeds extra tag images in the shares, and decodes the tag images by folding up a single tagged share. TVC can greatly increase the user-friendly for shares and enables users to recognize and manage various shares. Although the previous methods on TVC can improve user-friendly of the shares, these methods suffer a quality decreasing problem for recovered secret images. Therefore, this study proposes three various encryption approaches for threshold TVC schemes. First, this research achieves the better quality of revealing the tag image by improving the previous method. Second, this study develops a technology to add an adaptive ability for the threshold TVC schemes. The mechanism provides adjustability on display quality between recovered images and tag images of the TVC scheme. Finally, a novel encryption algorithm is proposed. The algorithm is based on the pixel swapping approach which swaps pixels on a conventional share such that a tag image can be embedded in the share. With this approach, the display quality of recovered image will be the same as that of the conventional visual cryptography schemes.
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Huynh, Ngoc-Tu, and 黃玉秀. "Visual Cryptography for Users Verification." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/20013477107564855623.
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碩士逢甲大學
資訊工程所
98
In this thesis, we propose two schemes. The first scheme is a new visual secret sharing scheme that cannot only be applied to grayscale images but also can be applied to binary and color images with low computational complexity. The proposed scheme allows senders to embed an n×n watermark image into an n×n secret image and generate two shadows. Each shadow is noise-like and leaks no information related to the original secret image. To increase the security of the secret image, torus automorphism is used to relocate its pixels during the shares construction phase. During the revealing and verifying phase, legitimate participants can extract the hidden watermark to verify whether the two collected shadows are authentic. Reconstruction of the secret image can be launched only when the two collected images are authenticated. Experimental results confirm that the secret image cannot be reconstructed if one of collected shadows is invalid. Even if one collected shadow is a valid shadow, it still cannot pass verification during the revealing and verifying phase. In other words, attackers cannot combine two valid shadows from two different secret images to forge a valid secret image. Moreover, our proposed scheme not only works well on grayscale images but also can be extended to binary images and color images with low computational complexity. The second scheme is an efficient secret sharing scheme without pixel expansion. The scheme first uses the VQ-compression method to compress a secret image. This allows senders to share a larger secret image than other methods. Moreover, the proposed method also allows participants to reconstruct a lossless secret image. The generated shadows are meaningful with high quality, so the image does not attract any suspicion from attackers.
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Chang, Chao-Yuan, and 張兆源. "Visual Cryptography for Color Images." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/89425490696775605858.
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Jiang, Chang-Ruei, and 蔣昌叡. "A Novel Verifiable Visual Cryptography." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/48733696997367627328.
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碩士銘傳大學
資訊工程學系碩士班
102
Visual cryptography proposed by Naor and Shamir in 1995 encrypts a secret among several shares and decrypts the secret by observing the stacked shares using human visual system. After two encoded share are produced from the secret image by Noar and Shamir’s scheme, we stamp a specific verifiable image onto the shares such that the result of two superimposed shares reveals the secret image, while that of one one and the other shifted shares reveals the verifiable image. In this proposed, we focus on the security of verifiable visual cryptography schemes. Base on stamping verifiable image on shares, we present a novel verifiable visual cryptography scheme with high security. Our scheme takes neither extra pixel extention nor extra verify shares.
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Tsai, Dushiau, and 蔡篤校. "On Cheating in Visual Cryptography." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/73127035023480845097.
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碩士國立中興大學
資訊科學研究所
91
A secret sharing scheme allows a secret to be shared among a set of participants, P, such that only authorized subsets of P can recover the secret, but any unauthorized subset can not recover the secret. In 1994, Noar and Shamir proposed a variant of secret sharing scheme called k-out-of-n threshold visual cryptography where the shares given to participants are xeroxed onto transparencies. If more then k transparencies are stacked together, the secret message can visually recovered by anyone without any cryptographic knowledge and without performing any cryptographic computation. In this thesis, we consider the cheating problem in visual cryptography. We show that cheating is possible when the cheaters form a coalition to deceive honest participants. For preventing cheating, an explicit definition of cheating is given; moreover, two cheating protection schemes are proposed to safeguard the honest participants in visual cryptography.
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Lee, Yao-Ting, and 李曜廷. "Visual Cryptography With Identifiable Shares." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/87030647164058874207.
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碩士元智大學
資訊工程學系
98
The thesis proposes a visual cryptography (VC) scheme with identifiable shares. In the proposed (t, n), 2 ? t ? n sharing method, the input image O is encoded in n shares that exhibits the following features: (1) each share is the same scale as O and has noise-like appearance, (2) stacking t?1 or less shares reveals no secret, (3) the secrets can be revealed by superimposing t or more shares, (4) folding a share up can disclose some tag patterns, and (5) both of the secret information and the tag patterns are recognized by naked eye without any computation. The property to show up tag patterns on folded shares is a new concept in visual cryptography scheme. The tag patterns provide diverse capabilities to the VC scheme, such as (1) augmented message to the secret information, (2) a simple and user-friendly interface for managing the numerous shares created by VC schemes, and (3) evidence for verifying consistency among those shares cooperating in a decoding instance. A (2, 2) sharing scheme using random grids and another (t, n) VC method based on probabilistic VC are implemented. Simulation results show that both the revealed secret messages and tag patterns can be recognized easily by naked eye, and no regular patterns are appeared if less than t shares are stacked, demonstrating the feasibility and high security of the proposed scheme.
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Wang, Shih-Ying, and 王詩瑩. "A Survey on Visual Cryptography." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/12737182217398353460.
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碩士銘傳大學
資訊工程學系碩士班
98
A new type of visual cryptography (VC) called visual secret sharing scheme (VSSS), was first introduced by Noar and Shamir [12] in 1994. The secret sharing schemes in conventional visual cryptography are characterized by encoding one secret or secrets into a set of random transparencies (shares) which reveal the secret to the human visual system when they are superimposed. Since Noar and Shamir proposed the basic model, reserchers have published many related studies. The binary VSSS of 2-out-of-n, n-out-of-n, and k-out-of-n, extended visual cryptography scheme (EVCS), clolored VSSS and there are some of studies proposed sharing multiple secrets. In this paper, we present how to make schemes and compare their results.
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Chueh, Shi-Kai, and 闕士凱. "Extended Region Incrementing Visual Cryptography." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/45568909692321027534.
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碩士銘傳大學
資訊工程學系碩士班
100
Visual secret sharing is the technique that can encode a secret image into several noise-like shares. Stacking all of the shares, the secret image can be decoded by human visual system. The region incrementing visual cryptography is one of visual secret sharing technique which can divide a secret image into several security levels, and encodes it into several noise-like shares. In decode process, the security levels can be incrementally revealed when the more shares are stacked. In this thesis, an extended region incrementing visual cryptography based on random grids scheme is proposed. This scheme can generate 1 to 3 security levels shares that have not only one or more meaningful messages but also need not to expand the pixel of share.
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Bhuyan, Sangeeta. "Image Security using Visual Cryptography." Thesis, 2015. http://ethesis.nitrkl.ac.in/7924/1/632.pdf.
Full textAbstract:
Informations are being transferred through open channels and the security of those informations has been prime concerns. Apart from many conventional cryptographic schemes, visual cryptographic techniques have also been in use for data and information security. Visual cryptography is a secret sharing scheme as it breaks an original image into image shares such that, when the shares are stacked on one another, a hidden secret image is revealed. The Visual Cryptography Scheme is a secure method that encrypts a secret document or image by breaking it into image shares. A unique property of Visual Cryptography Scheme is that one can visually decode the secret image by superimposing shares without computation. Even to make the visual cryptography image shares more secure, public key encryption scheme is applied. Public key encryption technique makes image shares so secure that it becomes very hard for a third party to decode the secret image information without having required data that is a private key.
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Chang, Tsai-Hua, and 張財華. "A Study on Color Visual Cryptography." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/62934932491947320178.
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碩士國立交通大學
資訊科學系
88
Original visual cryptography is to transform the secret message that we want to hide into several different binary images. To decode the message, we only have to stack two or several images together, then the secret message can be read by human visual system. However, this kind of methods is only suitable for some special types of secret messages including binary images, text, numbers or symbols. It cannot be applied to encode color images. In this paper, we will propose an efficient color visual cryptography scheme, which can encode and decode color secret message. And by controlling coding pixels, the colors on the recovered secret message will get closed to those in the original ones. In the meantime, based on the proposed method, some applications will also be introduced.
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Yu, Shih Chieh, and 游士杰. "A Cryptosystem Based on Visual Cryptography." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/78578611784934105156.
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碩士國立中興大學
資訊科學學系
86
1994年Naor和Shamir提出視覺加解密方式,基本上此種方式是門檻方法的 一個應用,它的基本雛型簡單言之包含一個存在於紙上的資訊M和一張做為 秘密金匙的投影片S,當M和S重疊時藉由人眼便能得知秘密影像為何.傳統 的加解密系統在加解密的過程中,都須要藉助電腦的運算,並非是由人腦所 能駕馭,所以相對而言視覺加解密的方式就顯得簡單的多了,解密過程只須 重疊投影片,不過Naor和Shamir所提的是屬於類似隨用即丟之方式,可能是 這次做完加解密程序後就不再重覆使用相同的金匙解密.在此提出架構在 視覺加解密理論的加解密系統,這是一個對稱性加解密系統,不過建構方式 是別於已往的運算方式而以Naor和Shamir的方式取代之.和傳統加解密系 統不同的是通訊的資料是影像,利用此點我們可用傳真機傳遞資料以增簡 便性.在這篇論文的第二章是介紹視覺加解密的理論及所用到的基礎概念, 第三章談利用Naor和Shamir的方式來架構出一套加解密系統並探討金匙的 持續使用性,而第四章的多人共用秘密影像係利用第三章的概念所構築而 成,我們將這架構和DES做比較,第五章根據傳統金匙加解密系統的優缺點 來探討第三章所提之系統,第六章為結論. In 1994,Naor and Shamir proposed Visual Cryptography (VC) theory that is anapplication of threshold scheme. To put it simply , the prototype of VC c-onsists of a printed page of ciphertext and a printed transparency serves as decrpted key. Upon receiving the ciphertext, we can stack the ciphertext and the transparency to gain the secret with eyes . In conventional cryptosystem , we have to do crypting operation with the computer. Ho-wever , it is simple for human to do decrypting operation in VC,because we can stack transparencies to achieve the decrypting operation. The method of Na-or and Shamirs'' is like one time pad , it does not do the crypting operationwith the same key.We propose a cryptosystem based on visual cryptographictheory of Naor and Shamir . We construct this cryptosystem as a symm-etric one , naturally, it bases on VC theory .In this structure, we can u-se fax machine to achieve communication .
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Wu, Chih-Cheng, and 吳志成. "Visual Cryptography and Secret Image Sharing." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/6t9dm3.
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博士國立東華大學
資訊工程學系
102
A so-called secret image sharing (SIS) shares a secret image into some shadow images (referred to as shadows) that distributed to participants. A set of qualified participants can recover the secret image, while non-qualified subsets of participants have no information about the secret image. The SIS scheme is usually referred to as a (k, n)-SIS scheme, k n, in which k is a threshold value to reveal the secret and n is the total number of shadows. SIS schemes can overcome the weakness of simply copying secret image, and meantime have the fault tolerance capacity due to the threshold property. Recently, SIS schemes have drawn increased attention. There are two major categories of SIS schemes: one is the polynomial SIS (PSIS) scheme and the other is the visual cryptography schemes (VCS). PSIS schemes can recover distortion-less secret image, but need using complex computation. Contrarily VCS has stacking-to-see property; however it has the poor visual quality of reconstructed image due to the shadow expansion. Therefore, many researches on VCS are dedicated on enhancing the contrast or reducing the shadow expansion. In this dissertation, we have seven main contributions about SIS schemes: (1) region-based progressive VCS. (2) block-based progressive VCS. (3) extension of (k, k) probabilistic VCS (PVCS) to (k, n)-PVCS. (4) using PVCS to construct all random grids, and theoretically proving that random grid is the subset of PVCS. (5) combining the watermarking and VCS to provide digital copyright. (6) essential SIS scheme. (7) matrix-based (2, n) SIS scheme. Some schemes are proposed to enhance the security and improve the efficiency of previous scholars SIS schemes. And, some are novel and new schemes. We sincerely hope that our results may increase research coverage, and can also give intended applications for SIS schemes.
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Torng, Ru-fang, and 童如芳. "Binary Transforms, Watermarking and Visual Cryptography." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/71838357656874690783.
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Lan, Yung-Ching, and 藍永青. "Incrementing Visual Cryptography Using Random Grids." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/21550618150327705681.
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碩士元智大學
資訊工程學系
97
Visual cryptography (VC) is an image-based secret protection mechanism in which the decoding process is conducted by inspecting the stacked shares with the unaided eye without any computation. In traditional VC schemes, the content of an image is usually processed as a single secret, which limits the whole image to a unique secret property. Recently, Wang et. al. [27] proposed a multilevel VC scheme in which the secrets on the original image are concealed in such a way that more levels of secrets are revealed when more shares are engaged in the decoding process. The scheme endows an image with multiple secret levels in VC applications; however, it also suffers from two weaknesses: (1) the pixel expansion is large, and (2) the contrast varies among the regions of different secret levels on the stacked images. In this study, we propose a non-expansible VC scheme using the concept of random grids with the ability of incremental revealing of the secrets. In the proposed n-level incrementing VC using random grids, the secret image S is designated to multiple regions associated with n secret levels, and encrypted to n+1 shares which exhibits the following properties: (1) each share has noise-like appearance and cannot obtain any secret in S, (2) the size of each share is the same as S, (3) any t (2≦t≦n+1) shares can be used to reveal up to t-1 levels of secrets, (4) all secrets in S can be disclosed when all of the shares are available, (5) all of the regions containing not-revealed-yet secrets have same contrast with the background on the stacked shares, and (6) the decoding process is done by inspecting the well-stacked shares with unaided eye without computer computation.
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Chiang, Su-Chen, and 江素貞. "Visual Cryptography Using Q'tron Neural Networks." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/24467923987133795674.
Full textAbstract:
博士大同大學
資訊工程學系(所)
92
Visual cryptography is a cryptographic scheme to achieve secret sharing. For example, it decomposes a secret image into n shares which are distributed to the participants, such that only qualified subsets of participants can "visually" recover the secret image. The "visual" recovery consists of xeroxing the shares onto transparencies, and then stacking them. The secret image will reveal without any cryptographic computation. Originally, the cryptographic paradigm introduced by Naor and Shamir has some drawbacks. This dissertation proposes a novel technique using neural networks (NNs) to fulfill visual cryptography schemes with some extended capabilities: i) the access schemes are described using a set of graytone images, and ii) the codebooks to fulfill them are not required; and iii) the size of share images is the same as the size of target images. The neural network model to conduct this research is called quantum neural-network (Q'tron NN; for short) model. It is an energy-driven NN model. A Q'tron NN is able to achieve local-minima free if it is constructed as a known-energy system and noise-injected, to be detailed in the dissertation. To fulfill an access scheme of visual cryptography, two energy sub-terms, which describe the image-halftoning rule and share-stacking rule, are considered to build the Q'tron NN. The proposed Q'tron NN structures are quite general and, hence, can be applied to fulfill any access schemes of visual cryptography. Some applications of visual cryptography based on the Q'tron NN approach are also discussed, including message concealment, visual authorization, and semipublic encryption.
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CAI, WEI-JHE, and 蔡瑋哲. "Application of Visual Cryptography in Watermarking." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/51261360970268914692.
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碩士吳鳳科技大學
光機電暨材料研究所
101
Abstract The exchange of information becomes increasingly easy in cyber space with the booming of computers and smart phones. All people have to do is to upload images in digital data through network access to an online platform. However, there are concerns hidden behind this convenience. For example, one may hold the uploaded images for one’s own purpose without the permission of the original owner. Theft and tempering are the most common cases seen in cyber space. To solve the problems like these, a digital watermarking technique was developed. Therefore, when an image has a digital watermark embedded, the information embedded in the original image will be copied altogether. If there is a dispute, the watermark is extracted to protect the rightful owner of the copyright and portraiture right as a certification mechanism. However the action to embed information in the original image may damage its quality. As a result, the study was intended to preserve the quality of image after embedment and the recognition of the watermark after extraction. The watermark proposed here is different from the traditional ones because it is based on visual cryptography. A visually cryptographic watermark reduces the amount of information storage compared to traditional ones, and it requires less complicated calculations. Instead, it overlaps images for decryption, and experiments were performed to prove that it did improve the image quality and resistance. Keywords: Visual Cryptography, Watermark
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Cai, Song-Ruei, and 蔡松叡. "Revisiting Boolean-Operation Based Visual Cryptography." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/44869015760739050102.
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碩士國立東華大學
資訊工程學系
103
Visual Cryptography Scheme (VCS) is provided with two important characteristics. One is based on pixel-wise operation, and the other is is decoding without computer (i.e., the stacking-to-see property). Generally, the so-called Boolean-operation based image processing schemes, e.g., ata hiding, digital watermarking, image sharing, encryption, adopt bit-wise operations. Even though the logic operation is very simple, it still needs a computer and an image editing program to deal with. For example a bit-wise OR operation of a pixel, the pixel need to be subdivided into 8 bit-planes and then uses OR operation. And, this needs the help of computer. In the he traditional VCS, the OR operation can be represented to stacking their shadow images and put them on overhead projector to visually decode the secret. This is the pixel-wise OR operation. Therefore, the traditional VCS is referred to as OVCS. As we know, the XOR operation can be represented by OR and NOT, where the NOT operation can be implemented by a device with the function reversing color, such as copy machine and optical interferometer. Thus, the XOR-based VCS (XVCS) is discussed recently. The previous work showed that base matrices of OVCS satisfy security and contrast conditions of XOR, and the contrast is enhanced 2^(k−1) times. In this thesis, we define two new Boolean-operation based VCSs, AND-based VCS (AVCS) and NOT-based VCS (NVCS). We will define security and contrast conditions of AVCS and XVCS, and also prove basis matrices of OVCS satisfy AVCS and NVCS. Our research results impliy that we can adopt two decoding options in VCS. Also, we will show how to properly use these Boolean-operation based VCSs for decoding. Since that the perfect whiteness is achieved in AVCS, we also defined a new contrast measurement by taking into account the perfect whiteness.
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Patel, Mahesh Kumar Desmedt Yvo. "A modernized version of visual cryptography." 2003. http://etd.lib.fsu.edu/theses/available/etd-08282003-200024.
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Thesis (M.S.)--Florida State University, 2003.Advisor: Dr. Yvo Desmedt, Florida State University, College of Arts and Sciences, Department of Computer Science. Title and description from dissertation home page (viewed Sept. 24, 2003). Includes bibliographical references.
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Quan, Zen-Yu, and 官振宇. "Friendly and Unexpanded Progressive Visual Cryptography." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/76800869430825588777.
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碩士淡江大學
資訊管理學系碩士班
97
Visual cryptography is a kind of data encoding method, which is encoding secret image into n pieces of noise-like shares and distributed them to every participator, and through stacking these shares to decode it directly by human eyes. As long as there are over k participators, the secrets are able to be decoded, while less than k can not. This is called (k, n)-threshold visual secret sharing (VSS) scheme. Yet progressive visual cryptography is dfferent from traditional VSS, which is decoding secret gradually by superimposing 2 or more pieces of shares. When more shares are being stacked, the outline of the secret will get clearer. Although the content of progressive visual cryptography studies have transferred from noise-like shares to meaningful stego ones, the sharing way is still based on pixel-expansion, therefore the sizes of shares expand to m times compared to original image. While recovering a secret image, it causes a bad quality because black pixel cannot be sure being reconstructed totally. Besides, due to there is only one sort of stego form, supervisors cannot know which participators have actually involved in, and it could bring about management problems. In order to solve the above problems, our research is in compliance with the theory of progressive visual cryptography to propose an image sharing method with pixel non-expansion as well as meaningful shares; in addition, the content of meaningful shares expands from only single image to many different disguised images. Following the numbers of shares is adding, the contour of the secret image will be more obvious, also the recovered black pixels can be ensured to be totally black and can produce a better quality of color contrast in both stego shares and secret image, which represent (i-1)/(n+i) and (n-1)/(n+i), and able to appears the contents clearly. Moreover, sharing matrix is designed to be expandable and variable in our study to adjust color contrast of both shares and recovered image based on user needs.
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Liao, Jung-Kuo, and 廖榮國. "Visual Cryptography with Arbitrary Privilege Levels." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/8kp83n.
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碩士國立東華大學
資訊工程學系
105
Visual Cryptography Scheme (VCS) is based on pixel-wise operation, which can be easily implemented without computer. In a (k, n)-VCS, a secret image is encoded into n shadow images that distributed to n participants. Any k participants can reveal the secret image by stacking their shadow images and decode the secret image via human visual sight, but (k-1) or fewer participants will not gain any secret information. This simple decoding way is the so-called stacking-to-see property, on which VCS can be applied on visual authentication, digital watermarking, security display, and embedding private information. Recently, Hou et al. introduced a (2, n) privilege-based VCS (PVCS) with various privilege levels of shadow images. In Hou et al.’s (2, n)-PVCS, a shadow with a higher privilege contributes more recovered information, while a lower privileged shadow has the less recovery capability. The threshold of (2, n)-PVCS is two, and thus two or more participants can reconstruct the secret image. Moreover, the visual quality of stacked result depends on the total sum of privilege levels for all involved shadows in reconstruction. Unfortunately, Hou et al.’s (2, n)-PVCS has the inconsistency of the contrast of recovered image and the sum of privilege levels. Accordingly, an enhanced Hou et al.’s (2, n)-PVCS (for short, Hou et al.’s (2, n)-EPVCS) is proposed to solve this inconsistency problem. However, Hou et al.’s EPVCS is not a general solution to implement all PVCSs with arbitrary privilege levels, and it also has the unequal whiteness of shadows. In this thesis, we also propose a new (2, n)-PVCS to solve these two critical problems.
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Yu, Chin-Sun, and 余慶杉. "An identification scheme based on visual cryptography." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/66199265823412300307.
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碩士國立中興大學
資訊科學學系
86
Human identification is very important in our daily life. It''s also ubiquitous in communication over insecure networks. Although it has received wide interestin cryptography research and studied extensively,there has been no satisfactory solution without using auxiliary devices,such as trusted computational device.In this thesis we propose a new identification method based on the idea of visual cryptographyto enable a human prover to identify himself to a verifier in an insecure environment without any help of auxiliary devices. Our method is secure against replay attack、wire tapping、impersonation attack, and can achievesystem authentication. Moreover,it is very cheap and can be implemented easily.
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Liu, Yi-Cheng, and 劉益成. "A Neural Network Approach for Visual Cryptography." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/98972956954598899335.
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碩士大同工學院
資訊工程研究所
87
Visual cryptography is a cryptographic scheme to achieve visual secret sharing. Roughly speaking, it is a technique to hide the information in a secrete image by distributively recording its content inside a set of shares, which are binary images printed on transparencies. Unless acquiring enough number of shares and stacking them together, it gives no clue for viewers to guess the secrete. More complex access schemes require that the stacking of different subsets of shares forms different target images. In the thesis, we propose a novel approach to reach the goal using neural networks (NNs). The neural network model to conduct this research is the so-called Q-state neural network (Q'tron NN; for short) model. Using such an neural network model, the problems with respect to various access schemes are reformulated as to minimize a cost function, which matches the energy function of a Q'tron NN. Accordingly, the Q'tron NN is then built to solve the problem. One remarkable feature of the Q'tron NN model is that the NN can incorporate with a persistent noise-injection mechanism to tune the solution quality, which corresponds to minimize the energy residing in the network to a certainly low level. To perform encrypting using such an NN, its input is a set of graylevel images. As the NN settles down, its output will be a set of binary images that fulfills the access scheme. This approach is considerably different from the traditional one, which constructs shares by assigning lengthy pixel codes to shares pixel by pixel based on the pixel values in a binary secrete image. For simple access schemes, such an approach is effective. For complex ones, it may be impotent because the code book corresponding a particular access scheme is hardly to be found or is even inexistent. Besides, such an approach will make the size of a share to be a multiple of the secrete image's. Another important topic to be discussed in the thesis is the so-called histogram allocation problem, which explores the strategies to judge whether an access scheme is realizable and to determine a feasible allocation of histograms for the set of graylevel images participating in the access scheme provided that the scheme is realizable. Visual cryptography finds many applications in cryptographic field such as key management, message concealment, authorization, authentication, identification, and entertainment. Other topics correlated with this research include the Hopfield neural network models, image halftoning and, contrast enhancement for images.
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Hsu, Yuan-Tai, and 許元泰. "A New Construction Algorithm for Visual Cryptography." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/78630232388119792519.
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碩士國立清華大學
資訊工程學系
92
Adi Shamir proposed a well-known technique for secret sharing. This technique can divide data D into n pieces in such a way that any k pieces can easily reconstruct D, but no information about D will be revealed even with complete knowledge of k-1 pieces. Such scheme is called a (k,n) threshold scheme. Naor and Shamir proposed further the idea of visual cryptography for sharing images. It can be seen as a visual variant of the k out of n secret sharing problem, in which each one of the n users gets a transparency; any k of them can see the image by stacking their transparencies, but any k-1 of them gain no information about it. In this paper a new construction algorithm of visual cryptography is presented. First, we extend SFCOD (Space Filling Curve Ordered Dither – one of the techniques of halftoning) to transform a gray-level image into an image with fewer grayscale values. In addition, we extend the basic visual cryptography model to handle more than two grayscale values. Then the extended visual cryptography model can be applied to encode this image. This scheme satisfies the security and contrast conditions. It can reveal more details of original images in the decoded images than ordinary visual cryptography scheme. At last, an extension of this scheme for color images is included.
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Chen, Tse-Shih, and 陳澤世. "Visual Cryptography Schemes with Small Shadow Size." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/6r27ze.
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博士國立東華大學
資訊工程學系
96
The Visual Cryptography Scheme (VCS) (or called Visual Secret Sharing (VSS) scheme) proposed by Naor and Shamir is a perfectly secure scheme to share a secret image. Unlike other secret sharing schemes, the VCS can be easily decoded by the human visual system when staking the shadows. By using m sub pixels to represent one pixel, we encrypt the secret image into several noise-like shadow images. The value of m is known as the pixel expansion. More pixel expansion increases the shadow size and makes VCSs impractical for real application. Therefore, we address the shadow expansion problems in VCSs. This dissertation contains five major parts: (1) the aspect ratio invariant VCS with small shadow size. (2) the VCS using different pixel expansion to reduce shadow size and simultaneously hold the contrast. (3) the VCS with the adjustable shadow size (4) the extended VCS with small shadow. (5) the color VCS with fixed pixel expansion. All results are dedicated on finding the less shadow size in VCSs and such that VCSs can be applied on the display in small devices, e.g., cellular phone, or monitor. Besides, combining the proposed small-shadow VCSs with watermarking or image indexing can enhance the quality of the stegoimage in these schemes. Moreover, it is interesting to hybrid VCSs with digital right management system for constructing a more simple and reliable system owing to the nature of VCSs (the perfect security and the easy decoding). The contrast of recovered image is poor and thus the VCS framework is always a research issue and does not have practical applications. Our researches, the less shadow size (or even any size) of shadow makes VCSs more practicable for applications.
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Lin, Che-Yu, and 林哲佑. "Almost Aspect Ratio Invariant Visual Cryptography Scheme." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/mxfrzc.
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碩士國立東華大學
資訊工程學系
102
A visual cryptography scheme (VCS) divides a secret image into some shadow images (known as the shadows) in a way that requires the shadows in a certain privileged coalitions for the secret reconstruction. However, the secret image cannot be revealed if they are not combined in the prescribed way. VCS has a novel stack-to-see property where decoding requires neither knowledge of cryptography nor computer. VCS is often used as a (k, n)-threshold scheme, where k is the threshold value to reveal the secret and n is the number of shadows. One can reconstruct a secret image by k or more shadows, while he cannot conjecture any information from less than k shadows. Generally, in (k, n)-VCS, a secret pixel is expanded into m secret pixels, so that the shadow size will be expanded m times. For the case, m is not a square number, hence the aspect ratio of reconstructed image will be distorted. Accordingly, an aspect ratio invariant VCS (ARIVCS) was proposed to address this distortion problem. However, a (k, n)-ARIVCS needs adding extra subpixels. In addition, it needs a complicated algorithm to find a mapping pattern showing how to arrange subpixels. Sometimes, m is too large that will bring a huge challenge. In this thesis, we propose the almost aspect ratio invariant VCS (AAIVCS) which simulated the principle of jigsaw puzzle. Our (k, n)-AAIVCS shows that no loss of aspect ratio can be almost achieved without adding extra subpixels. If the secret is allowed a little bit geometrically distorted, the proposed (k, n)-AAIVCS is very attractive since we do not need extra subpixels. Also, we theoretically prove that our construction method is the best way to achieve the less aspect ratio difference.
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Li, Fong-Jheng, and 李豐政. "On Visual Cryptography of Multiple Secret Images." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/k3qv8e.
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碩士國立交通大學
多媒體工程研究所
102
This master’s thesis proposes three schemes on visual cryptography of multiple secret images sharing: (2,2) model, constrained (2,3) model, and folding model. In the (2,2) model, we present two different schemes : 1) Multiple types of stacking: this method encodes twelve secret images into two transparencies. We can get twelve secret images respectively by eight different stacking types. 2) High hiding capacity: for four given secret images, two transparencies are produced. Stacking in different manners, we can decode four secret images respectively. Total space needed is smaller than the bits of total secret images. In constrained (2,3) model, the method encodes four secret images into three transparencies. We only can decode secret images by stacking the most important transparency with either one of the two other transparencies. This method can be extended into (2,k) model. Finally, in the folding model, we fold down a transparency, and then stack with the other to decode secret images.
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Chiou, Shan-Fu, and 邱善福. "The Analysis of New Visual Cryptography Scheme." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/00771957832898927770.
Full textAbstract:
碩士國立交通大學
資訊科學系
89
Visual cryptography is a method to encode a secret image into some secret image shares. Each participant receives a transparency that is printed some secret image share. Certain qualified subsets of participants can “visually” recover the secret image directly without knowing any knowledge of cryptography and performing any computations, but other sets, called forbidden sets, of participants have no information about the secret image, even to any cryptanalyst. The conventional definition of visual cryptography is limited to monotonic situation, and it is unreasonable about the part of “contrast”, for example, the recovered secret image is always darker than background after stacking transparencies, but we know that this is not necessary. No matter the recovered secret image is darker or lighter than background, we can recover the secret image by human visual system. New definition corrects this and makes it more general than conventional one. Based on the new definition, in this paper, we study the properties of new definition, propose a more efficient construction method, and show some results about comparison of two definitions.
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Chan, Yuan-Hao, and 詹原豪. "Visual Cryptography for 3-Dimensional Polygon Model." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/31897553347763531047.
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Wu, Jia-Hung, and 吳佳鴻. "Extended Visual Cryptography Scheme for Color Image." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/15977687926436314573.
Full textAbstract:
碩士國立中央大學
資訊管理研究所
91
Visual cryptography scheme has applied to color image. But extended visual cryptography scheme is still applied to binary image which each pixel on it is white or black. Now, the main contribution of this paper is to apply the extended visual cryptography for color image. Meanwhile, after the original images are encoded they are still meaningful, that is, anyone can recognize the images. After stacking the color share images, we can recognize the color secrete image.
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Huang, Min-Ming, and 黃酩閔. "The Image Watermarking Technique By Visual Cryptography." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/05615415304916227227.
Full textAbstract:
碩士國立屏東教育大學
資訊科學系碩士班
95
In our paper、we propose two watermarking mechanisms using visual cryptography. In the beginning、the same concept is that the original image is classified in terms of a certain process in every one of the two mechanisms. In the first method、we select blocks from the original image、and apply the discrete cosine transformation (DCT) to every block respectively. Then according to three coefficients of the low frequency in every block、we distribute the image blocks into six classifications. In the second method、we extract the four sub-bands LL3、LH3、HL3、and HH3 after applying the discrete wavelet transformation (DWT) two times. And we apply SOM to find out the potential features in the four sub-bands、and to group them into six classifications. Then、we construct the visual cryptography model with every type. Therefore、the watermark will be divided into the public share image and the secret share image by the model. When a controversy over the ownership of the host image happens、the copyright owner utilizes the proposed scheme to extract the public share from the host image、and superimpose the public share and the secret image so that can identify the ownership of the host image. Finally、experimental results show that the two proposed methods can resist several common attacks.
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Fan, Tzuo-Yau, and 范佐搖. "Digital Copyright Protection Based on Visual Cryptography." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/80741444381126028178.
Full textAbstract:
碩士銘傳大學
資訊工程學系碩士班
98
In this paper, several copyright protection schemes based on the visual cryptography technique and the discrete wavelet transform are proposed. The procedure of each proposed scheme can be approximately divided into two basic phases: the ownership image construction phase and the watermark retrieval phase. In the ownership image construction phase, the copyright mark or information is encoded as a verification code by the binary BCH code or the QR code. Using the n-level DWT decomposition skill, the creator has the feature from the protected image. The ownership image, which is used for the copyright protection, can be derived from the feature and the verification code by the visual cryptography techniques. In the watermark retrieval phase, the verification image can be derived from the feature of the attacked image by the visual cryptography techniques. Exactly superimposing the verification image and the ownership image, the attacked verification code can be obtained. Respectively adopting the BCH code or the QR code, the verifiable copyright mark or the verifiable copyright information can be found from the attacked verification code. From the experimental results, these proposed schemes can resist most image attacks.
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Lin, Yi-Chin, and 林易青. "Cheating Immune Block-based Progressive Visual Cryptography." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/70757100531708692175.
Full textAbstract:
碩士國立東華大學
資訊工程學系
101
In a (k, n)-VCS, any k participants can print out their shadows on transparencies and stack them on an overhead projector to visually decode the secret image without computer hardware or computation. Recently, Hou et al. introduced a (2, n) block-based progressive visual cryptographic scheme (BPVCS), which the image blocks can be gradually recovered step by step. In Hou et al.’s (2, n)-BPVCS, a secret image is subdivided into n non-overlapped image blocks. When stacking any t (2 t n) shadows, all the image blocks associated with these t participants will be recovered. Unfortunately, Hou et al.’s (2, n)-BVCPS suffers from the cheating problem, which any two dishonest participants might collude together to tamper their image blocks shared with other honest participants. Also, they can impersonate an honest participant to force other honest participants to reconstruct the wrong secret. In this thesis, we solve the cheating problem and propose a cheating immune (2, n)-BPVCS. Additionally, Hou et al.’s scheme is only suitable for the 2-out-of-n case, i.e., (k, n)-BPVCS where k=2. Here, we also present a (k, n)-BPVCS. The problem we consider in this thesis is that of constructing the cheating immune BVCPS that are robust against dishonest participants. This thesis has four main contributions: (1) we provide two cheating types in Hou et al.’s (2, n)-BPVCS (2) we propose a cheating immune (2, n)-BPVCS (3) we propose a general cheating immune (k, n)-BPVCS, where k and n can be any integers (4) our (2, n)-BPVCS and (k, n)-BPVCS are theoretically proven to satisfy the progressive recovery, the security, and the cheating immune capability.
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Chien, Chou-Yung, and 周咏蒨. "(k, n) Reversible AMBTC-based Visual Cryptography." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/e572vf.
Full textAbstract:
碩士國立東華大學
資訊工程學系
106
A (k, n) Visual Cryptography scheme (VCS) shares a secret image into n shadow images (referred to as shadows) in a way that requires the shadows in a predefined coalition for the secret reconstruction. However, the secret image cannot be revealed if they are not combined in the prescribed way. VCS has a novel stacking-to-see property where decoding requires neither knowledge of cryptography nor computer. The value of k is the threshold. The secret image can be reconstructed by k or more shadows, while it cannot be revealed from less than k shadows. Although VCS cannot obtain the distortion-less secret image, it provides both characteristics of "threshold property" and "stacking-to-see property", and thus may have many intended applications. Other VCS applications in combining electronic voting, watermarking, Google Street View, fingerprint, and barcode were also introduced. These applications come from the benefit of the decryption without computation, and meanwhile shadows are physically possessed by participants, which may not be compromised. Recently, Ou and Sun combined Visual Cryptography with compressed domains and proposed the reversible AMBTC Visual Cryptography scheme. Ou and Sun’ (2, 2) scheme shared the secret image into two AMBTC compressed images. The secret image can be reconstructed by OR (or XOR) operation, and meanwhile the AMBTC images can be obtained. In addition, Ou and Sun expanded their (2, 2)scheme to the (2, n) scheme, but participants need ⌈log2 N⌉ AMBTC compressed images. In this thesis, we propose the (k, k) threshold VCS to encode secret image into k AMBTC compressed images. Based on the (k, k) scheme and various values of n, we designed different methods to construct (k, n) scheme with the least compressed AMBTC images. Our main contributions have: (1) design base matrices of (k, k)-VCS satisfying AMBTC format, and (2) extend (k, k) scheme to (k, n) scheme. Experimental results demonstrate the effectiveness of our schemes, and theoretical analyses are also given.
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Lin, Yiming, and 林易民. "A Research of Visual Cryptography on XML Platform." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/60790336399281330368.
Full textAbstract:
碩士國立臺灣師範大學
資訊教育研究所
90
With the rapid-growing popularity of Internet, XML (Extensible Markup Language) becomes an important technical standard on World Wide Web. But the research of security on XML platform is not matured yet which can not provide necessary message security mechanism on Internet. In our research, we propose a secure information exchanging model which is called “X-Secure”. It has three main features. (1) By combining Visual Cryptography and XML Encryption Syntax, it provides the secure sharing mechanism which XML Encryption Syntax lacks. (2) We propose a novel encryption scheme (which is) called “Hybrid Encryption” and the scheme enables both men and computers to recognize the cipher text (which is) encrypted by Visual Cryptography. (3) Our Scheme includes PKI (Public Key Infrastructure) and Kerberos which provides a distributed security communication protocol on XML platform.
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Chen, Chun-Feng, and 陳群峰. "A New Resources Saving Scheme on Visual Cryptography." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/32625458453389794622.
Full textAbstract:
碩士中原大學
電機工程研究所
97
In this thesis, we propose an effective resource saving scheme on visual cryptography. Unlike traditional cryptography, visual secret sharing technology decodes a cipher text by using human’s eyes. It’s an excellent solution under the situation of not being able to decrypt by computer. Our proposed scheme is a brand new type of visual cryptography based on using pixel expansion method and changing turn angle method. For any two given square secret images, we use pixel expansion method to produce two corresponding transparencies S1 and S2. Both transparencies look noisy. When we stack the front views of both transparencies, the first secret image is obtained. Then we turn right ninety-degree on S2 and stack both transparencies again, the second secret image is obtained. In our proposed scheme, we also improve the noisy extent of share images. The contributions of our research are as follows: 1. In traditional visual cryptography, two share images can only be hidden one secret image. But in our proposed scheme, we can hide two secret images with two share images. 2. In traditional visual cryptography, hiding two secret images needs at least three share images, but we need only two share images on our proposed scheme. We can reduce amount of transparencies and black toner to reach to Energy Saving and Carbon Reduction purpose. We believe this study results will be probably practical and efficient to establish a useful visual cryptography scheme with above advantages in applications.
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Deng, Hong-Wen, and 鄧弘文. "Using Image Recognition Technology in Visual Cryptography Applications." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/hz8dyr.
Full textAbstract:
碩士淡江大學
資訊管理學系碩士在職專班
104
Visual cryptography is a type of cryptographic scheme, which hides secrets within multiple share images based at the pixel level. When a sufficient number of shares are stacked together, the secret can be recovered by the human eyes. These shares were conventionally printed out onto transparencies, but they encountered the inconvenience of keeping and carrying. The alignment difficulties also arose when superimposing transparencies. In the Internet era, although the problem of superimposing transparencies can be solved through computers, there are still other inconvenience interactions to suffer. This causes visual cryptography applications in practice always lacking the last push. To overcome the above obstacle, this study presents a feasible application schema for visual cryptography and develops a mobile app with innovations through image recognition technology. This allows each smartphone can be transformed into a decoding tool, which having the feature of “visible after scanning”. With this decoding tool, the visual secret sharing images do not need to be printed onto transparencies or continue saving in computers. Then they can be printed on plain paper, posters or billboards, or directly shown on the digital multimedia displays. For this change, this study further presents a novel method to generate the secret sharing image in full-color, which allows any full color pictures to be served as the cover images with significant visual meaning. It’s a new look different from the past, so you don’t need to superimpose transparencies in alignment difficulties anymore. Just scan the share images shown on paper or screen by picking up your smartphone whenever you want to recover the hidden secret. In this paper, we propose a mechanism for image processing which can be used on most smartphones, and also create an Android app having the feature of “visible after scanning”. This app can easily reveal the secret hidden within the share images. In addition, we provide a potential application for visual cryptography, so it is no longer limited to information security. It can be used as electronic coupons in marketing campaigns and accepted by most people.
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Yu, Kun Houng, and 余昆宏. "A Dual Digital Watermarking Based on Visual Cryptography." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/24537692744384883254.
Full textAbstract:
碩士嶺東科技大學
資訊科技應用研究所
97
This paper proposes a dual digital watermark scheme based on visual cryptography; two share images, which produced by visual secret sharing scheme, are used in this research; one is kept by owner; the other one is hidden in the middle-frequency components using the traditional Discrete Cosine Transform (DCT) that preserves the quality of the protected images. When verifying the copyright, the original images can be restored by applying the decryption rules of rotating share image and image differentiation method to the extracted hidden share image and copyright holder’s share image. This research shows the proposed technique achieves dual copyrights with characteristics.