Blockchain Papers

Xianfeng Zhao, Yingxia Dai, Dengguo Feng

No abstract is available for this record.

Raphaël C.‐W. Phan, Huo-Chong Ling

Recently, two generic watermarking protocols were proposed, based on a popular zero-knowledge identification protocol. In this paper, we show that both protocols are flawed and therefore fail to achieve their purpose of allowing a prover to prove to a verifier of his ownership of a watermarked image. We also give some suggestions to fix these flaws.

Yevgeniy Dodis, Shien Jin Ong, Manoj Prabhakaran, Arun Sahai

We investigate the feasibility of a variety of cryptographic tasks with imperfect randomness. The kind of imperfect randomness we consider are entropy sources, such as those considered by Santha and Vazirani, Chor and Goldreich, and Zuckerman. We show the following: (1) certain cryptographic tasks like bit commitment, encryption, secret sharing, zero-knowledge, non-interactive zero-knowledge, and secure two-party computation for any non-trivial junction are impossible to realize if parties have access to entropy sources with slightly less-than-perfect entropy, i.e., sources with imperfect randomness. These results are unconditional and do not rely on any un-proven assumption. (2) On the other hand, based on stronger variants of standard assumptions, secure signature schemes are possible with imperfect entropy sources. As another positive result, we show (without any unproven assumption) that interactive proofs can be made sound with respect to imperfect entropy sources.

JaeGwi Choi, Kyung-Hyune Rhee

In this paper, we are concerned with a digital fingerprinting scheme for multi-purchase where a buyer wants to buy more than a digital content. If we apply previous schemes to multi-purchase protocol, the number of execution of registration step and decryption key should be increased in proportion to that of digital contents to be purchased in order to keep unlinkability. More worse, most of fingerprinting schemes in the literature are based on either secure multi-party computation or general zero-knowledge proofs with very high computational complexity. These high complexities complicate materialization of fingerprinting protocol more and more. In this paper, we propose a multi-purchase fingerprinting scheme with lower computational complexity. In the proposed scheme, a buyer executes just one-time registration step regardless of the number of contents to be purchased. The number of decryption key is constant and independent of the number of contents to be purchased. We can also reduce the computational costs of buyers by introducing a concept of proxy-based fingerprinting protocol.

André Adelsbach, Markus Rohe, Ahmad‐Reza Sadeghi

Standard watermarking schemes suffer from a major problem: They require to reveal security critical information to potentially untrusted parties, when proving the presence of a watermark to these parties. Zero-knowledge watermark detection is a promising means to overcome this problem and to improve the security of digital watermarking schemes in the context of various applications: it allows to cryptographically conceal the information required for the detection of a watermark and to prove the presence of the hidden watermark by efficient zero-knowledge proof systems.However, concealing the watermark prevents the verifying party from performing additional checks on the watermark, e.g., on its probability distribution, which may be required for certain applications. This is a limitation in the use of zero-knowledge watermark detection and we present several strategies to overcome this issue.Furthermore, we propose concrete and practical protocols, which pursue two promising strategies: the first strategy is to prove in zero-knowledge that a concealed watermark suffices a certain desired distribution, whereas the second strategy is to interactively and verifiably generate watermarks that suffice the desired distribution.

Radu Sion, Mike Atallah, Sunil Prabhakar

Information, as an expression of knowledge is probably the most valuable asset of humanity today. By enabling relatively cost-free, fast, and accurate access channels to information in digital form, computers have radically changed the way we think and express ideas. As increasingly more of it is produced, packaged and delivered in digital form in a fast, networked environment, one of its main features threatens to become its worst enemy: zero-cost verbatim copies. The inherent ability to produce duplicates of digital Works at virtually no cost can be now misused e.g. for illicit profit. This dramatically increases the requirement for effective protection mechanisms. Different avenues are available, each with its advantages and drawbacks. Enforcement by legal means is usually ineffective, unless augmented by a digital counter-part such as Information Hiding. Digital Watermarking deploys Information Hiding as a method of Rights Protection to conceal an indelible rights witness (watermark) within the digital Work to be protected. The soundness of such a method relies on the assumption that altering the Work in the process of hiding the mark does not destroy the value of the Work, and that it is difficult for a malicious adversary (Mallory) to remove or alter the mark beyond detection without destroying the value of the Work. The ability to resist attacks from such an adversary (mostly aiming at removing the embedded watermark) is one of the major concerns in the design of a sound watermarking solution. With the notable exception of software watermarking, the overwhelming majority of research efforts have been invested in the framework of multimedia data (e.g. images, video and audio). In this work, I analyze digital watermarking from a higher level, domain-independent perspective. I propose a theoretical model [Sion et al, IEEE ITCC 2002] and in [Sion et al, SPIE 2004] ask: are there any limitations to what watermarking can do? What are these and when can they be reached? I then propose, design and analyze watermarking solutions for (i) numeric sets [Sion et al, IWDW 2002], (ii) numeric relational data [Sion et al, SIGMOD 2003, ICDE 2004], (iii) categorical data [Sion, ICDE 2004], (iv) streams [Sion et al, under review] and (v) semi-structures [Sion et al, IWDW 2003, NSF EIA-9903545]. I also explored the ability to hide information in natural language text [Atallah et. al., IHW02, Springer-Verlag], and developed a text tamper-proofing proof-of-concept [Naval Research grant N00014-02-1-0364/2002].

A. Adelsbach, Stefan Katzenbeisser, Ahmad‐Reza Sadeghi

No abstract is available for this record.

André Adelsbach, Ahmad‐Reza Sadeghi

Digital watermarking is a promising technology for protecting intellectual property rights on digital content. Resolving authorship-disputes was one of the first and most propelling applications of robust digital watermarks, and much research effort has gone into protocols for resolving authorship-disputes by means of digital watermarks. Unfortunately, previous proposals lack formal definitions of their trust model, their assumptions, and requirements they should fulfill. This lack of formal definitions makes security proofs for such protocols impossible and many dispute resolving protocols, claimed to be secure, can be shown to be insecure. In this paper we set off to rigorously defining dispute resolving schemes based on a reasonable formal definition of "authorship." Building on this formal fundament, we analyze the most important proposals for dispute resolving, and discuss their connection to our authorship model. We show that existing proposals suffer from two major problems: First, they require an unnecessary high level of trust in the dispute resolving party. The second and even more serious is that the winner of the dispute is not guaranteed to be the rightful author of the disputed work (conclusiveness problem). As solutions, we propose dispute resolving schemes based on zero-knowledge watermark detection and asymmetric watermarking schemes.

S. Armeni, D. Christodulakis, Ioannis Kostopoulos, Yannis C. Stamatiou · 5 authors

In this work, a method for proving copyright ownership is presented that is based on Zero Knowledge Interactive Proof (ZKIP) protocols for computationally intractable problems. The utilized problem is the 3-coloring problem, which consists in assigning one of three available colors to the vertices of a graph so that no two adjacent vertices have the same color. Using the presumed computational intractability of this problem, the construction of large signatures is proposed so that they represent adjacency matrices of random, 3-colorable graphs. Since it is easy to construct large graphs with a prescribed 3-coloring of their vertices whereas it is difficult to discover such a 3-coloring, the owner of a copyrighted digital piece of work (e.g. image, audio, video) may easily generate a random 3-colorable graph, embed it in the digital object and then use the knowledge of the 3-coloring in debates over the object’s ownership. Due to the intractability of the 3-coloring problem, only the owner is able to produce it sufficiently fast in an ownership challenge so as to convince a third party that the graph was indeed embedded in the object by herself/himself. Since graphs with maximum possible resistance to well-known coloring algorithms is required, we exploit some relatively recent experimental and theoretical findings suggesting that hard 3-coloring instances are found among graphs having a vertices to edges ratio around a specific threshold value. The proposed scheme has the additional advantage that disclosing the signature is of no consequences since it is essentially the knowledge of a characteristic of the signature, i.e. the 3-coloring of the graph it represents, that enables one to use it as proof of ownership of some digital object that contains it. Even if someone managed to locate and extract the signature, to use it would require a fast solution to a computationally intractable problem on some hard instance. Our proposal represents a shift from signatures that are simply viewed as bit sequences to signatures with properties that stem from their interpretation as instances of computationally intractable problems.

S. Armeni, Dimitris Christodoulakis, Ioannis Kostopoulos, Polychronis D. Kountrias · 6 authors

No abstract is available for this record.

H. Kinoshita

In conventional digital signature techniques, secret information, which is utilized for authentication, is disclosed to the verifier. A new digital signature system for image data is proposed. This system can be used to assert the copyright of image data. In this system, a graph generated from an image which must has a signature and an isomorphic graph is concealed in this image. The ZKIP (zero knowledge interactive proof) for the graph isomorphism is applied to assert the copyright of this image. Consequently the secret information is not disclosed during the authentication process.

Tong Zhang

In this paper, we introduce the concept of subliminal channels with its historical background and the major application as it being a kind of information hiding technology. We give the meaning of closing subliminal channels. After analyzing some failed schemes for closing subliminal channels, wepresent an improved Chaum's zero-knowledge proof protocol and a divertible protocol which can close the known subliminal channels.

Scott Craver, Stefan Katzenbeisser

Traditional watermarking systems require the complete disclosure of the watermarking key in the watermark verification process. In most systems an attacker is able to remove the watermark completely once the key is known, thus subverting the intention of copyright protection. To cope with this problem, public-key watermarking schemes were proposed that allow asymmetric watermark detection. Whereas a public key is used to insert watermarks in digital objects, the marks can be verified with a private key. Knowledge of this private key does not allow piracy. We describe two public-key watermarking schemes which are similar in spirit to zero-knowledge proofs. The key idea of one system is to verify a watermark in a blinded version of the document, where the scrambling is determined by the private key. A probabilistic protocol is constructed that allows public watermark detection with probability of 1/2; by iteration, the verifier can get any degree of certainty that the watermark is present. The second system is based on watermark attacks, using controlled counterfeiting to conceal real watermark data safely amid data useless to an attacker.

André Adelsbach, Ahmad‐Reza Sadeghi

No abstract is available for this record.

Daniele Micciancio

We describe a general technique to simplify as well as to improve several lattice based cryptographic protocols. The technique is rather straightforward and is easily applied to the protocols, and gives both a simpler analysis and better performance than the original protocols. The improvement is global: the modified protocols are simpler, faster, require less storage, use less bandwidth and need less random bits than the originals. Moreover, the improvement is achieved without any loss in security: we formally prove that the modified protocols are at least as secure as the original ones. In fact, the modified protocols might even be more secure as the adversary gets less information. We exemplify our technique on the Goldreich-Goldwasser zero-knowledge proof systems for lattice problems and the GGH public key cryptosystem. Partially supported by DARPA grant DABT63-96-C-0018 and NTT grant 67627-00. 1 1 Introduction Various cryptographic protocols based on the hardness of la...

Birgit Pfitzmann, Ahmad‐Reza Sadeghi

No abstract is available for this record.

Josep Domingo‐Ferrer

No abstract is available for this record.

Jau-Liang Chen, Tzonelih Hwang

No abstract is available for this record.

Stefano D’Amiano, Giovanni Di Crescenzo

No abstract is available for this record.

Josep Domingo‐Ferrer

No abstract is available for this record.