Blockchain Papers

V. Arvind, Bireswar Das

No abstract is available for this record.

Toru Nakanishi, Nobuo Funabiki

No abstract is available for this record.

Jens Groth, Rafail Ostrovsky, Amit Sahai

No abstract is available for this record.

Susan Hohenberger, Stephen A. Weis

No abstract is available for this record.

Moti Yung, Yunlei Zhao

No abstract is available for this record.

Luning Xia, Jiwu Jing

Access Control is an important mechanism of information security. Role-Based Access Control is a famous access control approach with good flexibility. RBAC96 and ARBAC97 are classical RBAC models. The ARBAC97 model facilitates decentralized administration of RBAC. However, ARBAC97 has some shortcomings in the case of being used in an organization with autonomous subsidiaries. The member of an administrative role can operate directly in the role range of a junior administrative role, which violates the autonomy of subsidiaries. We propose a new model named N-RBAC to overcome this weakness. In N-RBAC, roles are arranged according to a hierarchical namespace structure. Thus the role hierarchy is constructed in a local space instead of in a global space. The N-RBAC model does a better work in decentralized role administration in those organizations composed of autonomous subsidiaries.

Rosario Gennaro, Silvio Micali

No abstract is available for this record.

Jianzhong Zhang

A zero-knowledge proof scheme of identity authentication based on ElGamal digital signature is proposed,across zero-knowledge proof and smart card technology,we authenticate the user's identity efficiently and secretly.The scheme is secure under the assumption of the intractability of logarithm problems and the random oracle model.

Giuseppe Persiano, Ivan Visconti

No abstract is available for this record.

Jens Groth

No abstract is available for this record.

Dengguo Feng, Dongdai Lin, Moti Yung

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.

John Watrous

This paper proves that several interactive proof systems are zero-knowledge against general quantum attacks. This includes the well-known Goldreich–Micali–Wigderson classical zero-knowledge protocols for graph isomorphism and graph 3-coloring (assuming the existence of quantum computationally concealing commitment schemes in the second case). Also included is a quantum interactive proof system for a complete problem for the complexity class of problems having honest verifier quantum statistical zero-knowledge proofs, which therefore establishes that honest verifier and general quantum statistical zero-knowledge are equal: $\mathrm{QSZK}= \mathrm{QSZK}_{\mathrm{HV}}$. Previously no nontrivial interactive proof systems were known to be zero-knowledge against quantum attacks, except in restricted settings such as the honest verifier and common reference string models. This paper therefore establishes for the first time that true zero-knowledge is indeed possible in the presence of quantum information and computation.

Theodoros Balopoulos, Stephanos Gritzalis, Sokratis Katsikas

Esoteric protocols, such as electronic cash, electronic voting and selective disclosure protocols, use special message constructors that are not widely used in other types of protocols (for example, in authentication protocols). These message constructors include blind signatures, commitments and zero-knowledge proofs. Furthermore, a standard formalization of the Dolev-Yao intruder [6] does not take into account these message constructors, nor does it consider some types of attacks (such as privacy attacks, brute-force dictionary attacks and known-plaintext attacks) that esoteric as well as other types of protocols are designed to protect against. This paper aims to present an extension of typed MSR [3, 4] in order to formally specify the needed message constructors, as well as the capabilities of a Dolev-Yao intruder designed to attack esoteric protocols.

John Malone-Lee

No abstract is available for this record.

Tsuyoshi Yamamoto, Eiichiro Fujisaki, Masayuki Abe

No abstract is available for this record.

Andrew S. Patrick, Moti Yung

No abstract is available for this record.

Endre Bangerter

Diese Dissertation befasst sich mit effizienten zero-knowledge Beweisen von Wissen für Homomorphismen. Einerseits\nuntersuchen wir die Effizienzbeschränkungen bestehender Beweise von Wissen für Homomorphismen, andererseits\nbeschreiben wir neue Protokolle, welche diese Beschränkungen zu überwinden vermögen. Die Hauptresultate der Arbeit\nsind die Folgenden:\n- Alle effizienten Beweise von Wissen wurden, vor unserer Arbeit, mittels des Sigma Protokolls erzielt. Wir zeigen auf,\ndass für das Sigma Protokoll inhärente und demnach prinzipiell nicht überwindbare Effizienzbeschränkungen bestehen.\n- Insbesondere waren für die praktisch bedeutsame Klasse von Exponentiations-Homomorphismen in Gruppen unbekannter\nOrdnung (wie z.B., RSA- oder Klassengruppen) bisher keine effizienten zero-knowledge Beweise von Wissen bekannt. Wir\nbeschreiben neue Protokolle, die erstmalig effiziente zero-knowledge Beweise von Wissen für Exponentiations-\nHomomorphismen in Gruppen unbekannter Ordnung liefern.

Chunming Tang, Zhuojun Liu

Blum integers (BL), which has extensively been used in the domain of cryptography, are integers with form p , where p and q are di#erent primes both 3 mod 4 and k 1 and k 2 are odd integers. These integers can be divided two types: 1) M = pq, 2) M = p at least one of k 1 and k 2 is greater than 1.

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.

Pino Caballero‐Gil

The aim of this work is to investigate the possibility of designing zero-knowledge identification schemes based on hard-on-average problems. It includes a new two-party identification protocol whose security relies on a discrete mathematics problem classified as DistNP-Complete under the average-case analysis, the so-called Distributional Matrix Representability Problem. Thanks to the use of the search version of the mentioned problem, the zero-knowledge property is formally proved by black-box simulation, and consequently the security of the proposed scheme is actually guaranteed. Furthermore, with the proposal of a new zero-knowledge proof based on a problem never used before for this purpose, the set of tools for designing cryptographic applications is enlarged.

Tomohiro Onodera

In this paper, we propose a proof scheme of shuffle, which is an honest verifier zero-knowledge proof of knowledge such as the protocols by Groth and Furukawa. Unlike the previous schemes proposed by Furukawa-Sako, Groth, and Furukawa, our scheme can be used as the shuffle of the elements encrypted by Paillier's encryption scheme, which has an additive homomorphic property in the message part. The ElGamal encryption scheme used in the previous schemes does not have this property.