Blockchain Papers

Susan Hohenberger, Stephen A. Weis

No abstract is available for this record.

Abhilasha Bhargav-Spantzel, Anna Squicciarini, Elisa Bertino

We develop solutions for the security and privacy of user identity information in a federation. By federation we mean a group of organizations or service providers which have built trust among each other and enable sharing of user identity information amongst themselves. We first propose a flexible approach to establish a single sign-on (SSO) ID in the federation. Then we show how a user can leverage this SSO ID to establish certified and un-certified user identity attributes without the dependence on PKI for user authentication. This makes the process more usable and privacy preserving. Our major contribution in this paper is a novel solution for protection against identity theft of these identity attributes. We provide protocols based on cryptographic techniques, namely zero knowledge proofs and distributed hash tables. We show how we can preserve privacy of the user identity without jeopardizing security. We formally prove correctness and provide complexity results for our protocols. The complexity results show that our approach is efficient. In the paper we also show that the protocol is robust enough even in case semi-trusted "honest-yet curious" service providers thus preventing against insider threat. In our analysis we give the desired properties of the cryptographic tools used and identify open problems. We believe that the approach represents a precursor to new and innovative cryptographic techniques which can provide solutions for the security and privacy problems in federated identity management.

Theodoros Balopoulos, Stefanos Gritzalis, Sokratis Katsikas

Electronic voting, as well as other privacy-preserving protocols, use special cryptographic primitives and techniques that are not widely used in other types of protocols, e.g. in authentication protocols. These include blind signatures, commitments, zero-knowledge proofs, mixes and homomorphic encryption. Furthermore, typical formalizations of the Dolev-Yao intruder's capabilities do not take into account these primitives and techniques, nor do they consider some types of attacks that e-voting as well as other types of protocols are designed to protect against, such as privacy attacks due to undesired linkability of protocol executions. This work aims to extend Typed MSR so that it is able to support the specification of privacy-preserving protocols, as well as the capabilities of a Dolev-Yao intruder designed to attack such protocols.

Michael Backes, Jan Camenisch, Dieter Sommer

This paper introduces a novel approach for augmenting attribute-based access control systems in a way that allows them to offer fully anonymous access to resources while at the same time achieving strong accountability guarantees. We assume that users hold attribute certificates and we show how to exploit cryptographic zero-knowledge proofs to allow requesting users to prove that they hold suitable certificates for accessing a resource. In contrast to the commonly taken approach of sending all possibly relevant certificates to the access control system, our approach hence does not release any information to the access control system except for the presence of a set of certificates satisfying the access condition. This constitutes the minimal amount of information that has to be released for coming up with a correct access decision, and our approach is the first to achieve this. Additionally given a trusted third party for identity escrow, we furthermore show that a concise application of zero-knowledge proofs offers the access control system the capability to hold a requesting user accountable for her actions under specific, well-defined conditions. All the employed cryptographic techniques are highly efficient, and an architecture for exploiting our approach in practical scenarios is already in place.

Mauro Barni, Ingemar J. Cox, Ton Kalker, Hyoung Joong Kim

No abstract is available for this record.

Ashutosh Saxena, Ben Soh

Authentication forms the basis for most applications on the Internet. However, at the IP level, no solid mechanism yet exists for detecting 'spoofed' IP packets. The need for authenticating source IP addresses has become eminent with the advent of many ingenious DDoS attacks. In this paper, we propose a type of authentication scheme based on group (or multi party) signatures and discuss applications of such a scheme in preventing and detecting many types of DDoS attacks found on the Internet. Group signatures authenticate groups of senders rather than individuals and using such a scheme, senders can prove membership of a particular group without having to reveal their individual identity. The main idea behind our approach is to combine senders into large groups to reduce the amount of keying information kept in core routers. Our scheme also presents a method for secure routing protocols in general. Using our scheme, several autonomous networks can exercise policies on granting or denying routing privileges to other interconnected networks. Essentially, our protocol uses the concept of 'Non-interactive zero knowledge proofs of membership'

Luis von Ahn, Nicholas Hopper, John Langford

We introduce covert two-party computation, a stronger notion of security than standard secure two-party computation. Like standard secure two-party computation, covert two-party computation allows Alice and Bob, with secret inputs xA and xB respectively, to compute a function f(xA,xB) without leaking any additional information about their inputs. In addition, covert two-party computation guarantees that even the existence of a computation is hidden from all protocol participants unless the value of the function mandates otherwise. This allows the construction of protocols that return f(xA,xB) only when it equals a certain value of interest (such as "Yes, we are romantically interested in each other") but for which neither party can determine whether the other even ran the protocol whenever f(xA,xB) is not a value of interest. Since existing techniques for secure function evaluation always reveal that both parties participate in the computation, covert computation requires the introduction of new techniques based on provably secure steganography. We introduce security definitions for covert two-party computation and show that this surprising notion can be achieved by a protocol given the Decisional Diffie-Hellman assumption in the "honest but curious" model. Using this protocol as a subroutine, we present another protocol which is fair and secure against malicious adversaries in the Random Oracle Model --- unlike most other protocols against malicious adversaries, this protocol does not rely on zero-knowledge proofs (or similar cut-and-choose techniques), because they inherently reveal that a computation took place. We remark that all our protocols are of comparable efficiency to protocols for standard secure two-party computation.

Victoria Ungureanu

Delegation, whereby an entity gives some of its rights to other entities, is considered the cornerstone of decentralized authorization, and many access control frameworks proposed recently make delegation its central tenet. In these frameworks, delegation is commonly viewed as a transfer between two autonomous agents---the grantor and the grantee. But the situation can be considerably more complex, and more challenging, in the case the grantor belongs to an organization. Generally, employees are not autonomous agents, but their actions are subject to the regulations of their enterprise. In particular, if an employee transfers his rights to another agent, this transfer is subject to the enterprise delegation policies.In delegation frameworks, authorizing a request requires finding a valid chain of credentials that delegates the authority from the source (the local policy of the entity that serves the request) to the requester. Unfortunately, chain discovery is a computationally expensive and time consuming task. It was shown that, in the general case, chain discovery is undecidable, and in more restrictive cases, it is polynomial in the number of credentials available to the server. Verifying compliance with the terms of a delegation policy adds a considerable overhead to request authorization.This paper presents a framework that considerably reduces the time required to authorize a request. In this framework, a delegation chain is condensed into a single credential, called chained delegation certificate (CDC). A CDC attests that the owner has a certain right, and serves as proof that every link in the chain complies with the policy governing delegation of the right in question. When CDCs are used for authorization, a server does not need to verify compliance with the delegation policy, nor does it need to perform the chain discovery step, and therefore requests are served considerably faster.

Aneta Zwierko, Zbigniew Kotulski

No abstract is available for this record.

Victor K. Wei

In 1982, Chaum [21] pioneered the anonymous e-cash which finds many applications in e-commerce. In 1993, Brands [8--10] and Ferguson [30, 31] published on single-term offline anonymous ecash which were the first practical e-cash. Their constructions used blind signatures and were inefficient to implement multi-spendable e-cash. In 1995, Camenisch, Hohenberger, and Lysyanskaya [12] gave the first compact 2 -spendable e-cash, using zero-knowledge-proof techniques. They left an open problem of the simultaneous attainment of O(1)-unit wallet size and efficient coin tracing. The latter property is needed to revoke bad coins from over-spenders. In this paper, we solve [12]'s open problem, and thus enable the first practical compact e-cash. We use a new technique whose security reduces to a new intractability assumption: the Decisional Harmonically-Tipped Diffie-Hellman (DHTDH) Assumption.

Jens Groth

Abstract. A shuffle consists of a permutation and re-encryption of a set of input ciphertexts. One application of shuffles is to build mix-nets. We suggest an honest verifier zero-knowledge argument for the correctness of a shuffle of homomorphic encryptions. Our scheme is more efficient than previous schemes both in terms of communication and computation. The honest verifier zero-knowledge argument has a size that is independent of the actual cryptosystem being used and will typically be smaller than the size of the shuffle itself. Moreover, our scheme is well suited for the use of multi-exponentiation and batch-verification techniques. Additionally, we suggest a more efficient honest verifier zero-knowledge argument for a commitment containing a permutation of a set of publicly known messages. We also suggest an honest verifier zero-knowledge argument for the correctness of a combined shuffle-and-decrypt operation that can be used in connection with decrypting mix-nets based on ElGamal encryption. All our honest verifier zero-knowledge arguments can be turned into honest verifier zero-knowledge proofs. We use homomorphic commitments as an essential part of our schemes. When the commitment scheme is statistically hiding we obtain statistical honest verifier zero-knowledge arguments; when the commitment scheme is statistically binding we obtain computational honest verifier zero-knowledge proofs. Key words. Shuffle, Honest verifier zero-knowledge argument, Homomorphic encryption, Mix-net. 1

Douglas Wikström

We introduce the first El Gamal based mix-net in which each mix-server partially decrypts and permutes its input, i.e., no reencryption is necessary. An interesting property of the construction is that a sender can verify non-interactively that its message is processed correctly. We call this sender verifiability. The mix-net is provably UC-secure against static adversaries corrupting any minority of the mix-servers. The result holds under the decision Diffie-Hellman assumption, and assuming an ideal bulletin board and an ideal zero-knowledge proof of knowledge of a correct shuffle. Then we construct the first proof of a decryption-permutation shuffle, and show how this can be transformed into a zero-knowledge proof of knowledge in the UC-framework. The protocol is sound under the strong RSA-assumption and the discrete logarithm assumption. Our proof of a shuffle is not a variation of existing methods. It is based on a novel idea of independent interest, and we argue that it is at least as efficient as previous constructions.

Tassos Dimitriou, Dimitris Foteinakis

No abstract is available for this record.

Balaji Venkatachalam

No abstract is available for this record.

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].

Aggelos Kiayias, Yiannis Tsiounis, Moti Yung

No abstract is available for this record.

Ivan Damgård, Jens Groth, Gorm Salomonsen

No abstract is available for this record.

Jens Groth

No abstract is available for this record.

Wei Deng, Mingqi Chen, Bo Ai

In order to be competitive, telecommunications service providers need new technologies that facilitate the rapid introduction of new services and resolve the problems how to use the services safely. This paper introduces a network platform based on mobile agent and provides a security mechanism based on zero knowledge proof in the mobile communication system. In this way, service providers can provide the new services rapidly, expediently and safely.

Yong-Sork Her, 容碩 許, Kouichi Sakurai, 幸一 櫻井 · 5 authors

The voting plays important roles in a democratic country. Due to the problems of the existed voting m ethod, the new voting methods, electronic voting system, have been developing using the computer net work and cryptographic techniques. Many electronic voting schemes have been introduced for secure electronic voting systems. In this paper, we propose the secure electronic voting for absentee e-voting system. The absentee voting plays the important percentage in the existing voting system. But, the abs entee vote can not look forward to the security because of transmit by mail. The absentee does not kno w whether one’s voting is exactly counted or not. In this paper, we propose the absentee e-voting syste m based on security, completeness and verifiability. We use r-th residue cryptography for homomorphi c encryption, ZKIP (Zero-Knowledge interactive proofs), RSA algorithm. Also, we propose the ne w method of tallying for multi-candidate. The goals of out voting system are the absentee vot ing based on privacy, universal verifiability, reuseability and multi-candidate.

Yong-Sork Her, 容碩 許, キョ, ヨウソク, Kouichi Sakurai · 6 authors

In this paper, we propose the absentee e-voting system based on security, completeness and verifiability. We use r-th residue cryptography for homomorphic encryption, ZKIP (Zero-Knowledge interactive proofs), RSA algorithm for the secure absentee e-voting.

Peter Wayner

No abstract is available for this record.

Byoungcheon Lee, Kwangjo Kim

No abstract is available for this record.