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9,005 results ¡ page 337 of 376
Eli BenâSasson, Alessandro Chiesa, Daniel Genkin, Eran Tromer ¡ 5 authors
No abstract is available for this record.
Endre Bangerter, Stefania Barzan, Stephan Krenn, AhmadâReza Sadeghi ¡ 6 authors
No abstract is available for this record.
Sankita Patel, Viren Patel, Devesh C. Jinwala
No abstract is available for this record.
Xiang Xie, Rui Xue, Minqian Wang
No abstract is available for this record.
Marcin Andrychowicz, Stefan Dziembowski, Daniel Malinowski, Ĺukasz Mazurek
AbstractâBitcoin is a decentralized digital currency, intro-duced in 2008, that has recently gained noticeable popularity. Its main features are: (a) it lacks a central authority that controls the transactions, (b) the list of transactions is publicly available, and (c) its syntax allows more advanced transactions than simply transferring the money. The goal of this paper is to show how these properties of Bitcoin can be used in the area of secure multiparty computation protocols (MPCs). Firstly, we show that the Bitcoin system provides an attractive way to construct a version of âtimed commitmentsâ, where the committer has to reveal his secret within a certain time frame, or to pay a fine. This, in turn, can be used to obtain fairness in some multiparty protocols. Secondly, we introduce a concept of multiparty protocols that work âdirectly on Bitcoinâ. Recall that the standard definition of the MPCs guarantees only that the protocol âemulates the trusted third partyâ. Hence ensuring that the inputs are correct, and the outcome is respected is beyond the scope of the definition. Our observation is that the Bitcoin system can be used to go beyond the standard âemulation-basedâ definition, by constructing protocols that link their inputs and the outputs with the real Bitcoin transactions. As an instantiation of this idea we construct protocols for secure multiparty lotteries using the Bitcoin currency, without relying on a trusted authority (one of these protocols uses the Bitcoin-based timed commitments mentioned above). Our protocols guarantee fairness for the honest parties no matter how the loser behaves. For example: if one party interrupts the protocol then her money is transferred to the honest participants. Our protocols are practical (to demonstrate it we performed their transactions in the actual Bitcoin system), and can be used in real life as a replacement for the online gambling sites. We think that this paradigm can have also other applications. We discuss some of them. Keywordsâbitcoin; multiparty; lottery; I.
Maheswara Rao Valluri
Authentication is a process by which an entity, which could be a person or intended computer, establishes its identity to another entity. In private and public computer networks including the Internet, authentication is commonly done through the use of logon passwords. Knowledge of the password is assumed to guarantee that the user is authentic. Internet business and many other transactions require a more stringent authentication process. The aim of this paper is to propose two authentication schemes based on general non-commutative rings. The key idea of the schemes is that for a given non-commutative ring; one can build polynomials on additive structure and takes them as underlying work structure. By doing so, one can implement authentication schemes, one of them being zero-knowledge interactive proofs of knowledge, on multiplicative structure of the ring. The security of the schemes is based on the intractability of the polynomial symmetrical decomposition problem over the given non-commutative ring.
Kai-Min Chung, Edward Lui, Mohammad Mahmoody, Rafael Pass
Goldreich and Oren (JoCâ94) show that only trivial languages have 2-message zero-knowledge arguments. In this note we consider weaker, super-polynomial-time simulation (SPS), notions of zero-knowledge. We present barriers to using black-box reductions for demonstrating soundness of 2-message protocols with efficient prover strategies satisfying SPS zero-knowledge. More precisely, we show that assuming the existence of poly(T (n))-hard one-way functions, the following holds: ⢠For sub-exponential (or smaller) T (¡), polynomial-time black-box reductions cannot be used to prove soundness of 2-message T (¡)-simulatable arguments based on any polynomialtime intractability assumption. This matches known 2-message quasi-polynomial-time simulatable arguments using a quasi-polynomial-time reduction (Passâ03), and 2-message exponential-time simulatable proofs using a polynomial-time reduction (Dwork-Naorâ00, Passâ03). ⢠poly(T (¡))-time black-box reductions cannot be used to prove soundness of 2-message strong T (¡)-simulatable (efficient prover) arguments based on any poly(T (¡))-time intractability assumption; strong T (¡)-simulatability means that the output of the simulator is indistinguishable also for poly(T (¡))-size circuits. This matches known 3-message strong quasi-polynomial-time simulatable proofs (Blumâ86, Canetti et al â 00).
Xiao Qiang Guo, Li Hong Li, Cui Ling Luo, Yi Shuo Shi
The Bit Commitment (BC) is an important basic agreement in cryptography . The concept was first proposed by the winner of the Turing Award in 1995 ManuelBlum. Bit commitment scheme can be used to build up zero knowledge proof, verified secret sharing, throwing coins etc agreement.Simultaneously and Oblivious Transfer together constitute the basis of secure multi-party computations. Both of them are hotspots in the field of information security. We investigated unconditional secure Quantum Bit Commitment (QBC) existence. And we constructed a new bit commitment model â double prover bit commitment. The Quantum Bit Commitment Protocol can be resistant to errors caused by noise.
Nivedita Datta
In many applications, when communicating with a host, we may or may not be concerned about the privacy of the data but are mainly concerned about the integrity of data being transmitted. This paper presents a simple algorithm based on zero knowledge proof by which the receiver can confirm the integrity of data without the sender having to send the digital signature of the message directly. Also, if the same document is sent across by the same user multiple times, this scheme results in different digital signature each time thus making it a practical one-time signature scheme.
Man Ho Au, Willy Susilo, Yi Mu, Sherman S. M. Chow
Dynamick-times anonymous authentication (k-TAA) schemes allow members of a group to be authenticated anonymously by application providers for a bounded number of times, where application providers can independently and dynamically grant or revoke access right to members in their own group. In this paper, we construct a dynamick-TAA scheme with space and time complexities ofO(log(k)) and a variant, in which the authentication protocol only requires constant time and space complexities at the cost ofO(k) -sized public key. We also describe some tradeoff issues between different system characteristics. We detail all the zero-knowledge proof-of-knowledge protocols involved and show that our construction is secure in the random oracle model under theq-strong Diffie-Hellman assumption andq-decisional Diffie-Hellman inversion assumption. We provide a proof-of-concept implementation, experiment on its performance, and show that our scheme is practical.
Kai-Min Chung, Rafael Pass, Karn Seth
The simulation paradigm, introduced by Goldwasser, Micali and Racko , is of fundamental importance to modern cryptography. In a breakthrough work from 2001, Barak (FOCS'01) introduced a novel non-black-box simulation technique. This technique enabled the construction of new cryptographic primitives, such as resettably-sound zero-knowledge arguments, that cannot be proven secure using just black-box simulation techniques. The work of Barak and its follow-ups, however, all require stronger cryptographic hardness assumptions than the minimal assumption of one-way functions: the work of Barak requires the existence of collision-resistant hash functions, and a very recent result by Bitansky and Paneth (FOCS'12) instead requires the existence of an Oblivious Transfer protocol. In this work, we show how to perform non-black-box simulation assuming just the existence of one-way functions. In particular, we demonstrate the existence of a constant-round resettably-sound zero-knowledge argument based only on the existence of one-way functions. Using this technique, we determine necessary and su cient assumptions for several other notions of resettable security of zero-knowledge proofs. An additional bene t of our approach is that it seemingly makes practical implementations of non-black-box zero-knowledge viable.
Jannik Dreier, JeanâGuillaume Dumas, Pascal Lafourcade
Auctions have a long history, having been recorded as early as 500 B.C. [Auction Theory, Academic Press, San Diego, USA, 2002]. Nowadays, electronic auctions have been a great success and are increasingly used in various applications, including high performance computing [Concurrency and Computatio n: Practice and Experience 14(13â15) (2002), 1507â1542]. Many cryptographic protocols have been proposed to address the various security requirements of these electronic transactions, in particular to ensure privacy. Brandt [International Journal of Information Security 5 (2006), 201â216] developed a protocol that computes the winner using homomorphic operations on a distributed ElGamal encryption of the bids. He claimed that it ensures full privacy of the bidders, i.e. no information apart from the winner and the winning price is leaked. We first show that this protocol â when using malleable interactive zero-knowledge proofs â is vulnerable to attacks by dishonest bidders. Such bidders can manipulate the publicly available data in a way that allows the seller to deduce all participantsâ bids. We provide an efficient parallelized implementation of the protocol and the attack to show its practicality. Additionally we discuss some issues with verifiability as well as attacks on non-repudiation, fairness and the privacy of individual bidders exploiting authentication problems.
Chengdong Meng, Zhengyong Zhang, Rong Hu, Yongxiang Yang
DAA (Direct Anonymous Attestation) schemes are generally employed with the hardware of TPM to realize anonymous authentication. Basically, DAA schemes are based on group signatures. We propose a new DAA scheme based on a short group signature without encryption which departs from the traditional sign-encrypt-prove paradigm, only adopts an anonymous signature and non-interactive zero knowledge(NIZK) proofs. Compared to other DAA schemes at present, our scheme is approximately the most efficient and computational cost-saving with shorter signature length and easier signature generation. Our scheme also satisfies anonymity, trace ability and non-frame ability requirements.
JosÊ Bacelar Almeida, Manuel Barbosa, Endre Bangerter, Gilles Barthe ¡ 6 authors
Developers building cryptography into security-sensitive applications face a daunting task. Not only must they understand the security guarantees delivered by the constructions they choose, they must also implement and combine them correctly and efficiently. Cryptographic compilers free developers from this task by turning high-level specifications of security goals into efficient implementations. Yet, trusting such tools is hard as they rely on complex mathematical machinery and claim security properties that are subtle and difficult to verify. In this paper we present ZKCrypt, an optimizing cryptographic compiler achieving an unprecedented level of assurance without sacrificing practicality for a comprehensive class of cryptographic protocols, known as Zero-Knowledge Proofs of Knowledge. The pipeline of ZKCrypt integrates purpose-built verified compilers and verifying compilers producing formal proofs in the CertiCrypt framework. By combining the guarantees delivered by each stage, ZKCrypt provides assurance that the output implementation securely realizes the abstract proof goal given as input. We report on the main characteristics of ZKCrypt, highlight new definitions and concepts at its foundations, and illustrate its applicability through a representative example of an anonymous credential system
Ghassan Karame, Elli Androulaki, SrÄjan Äapkun
Bitcoin is a decentralized payment system that relies on Proof-of-Work (PoW) to verify payments. Nowadays, Bitcoin is increasingly used in a number of fast payment scenarios, where the time between the exchange of currency and goods is short (in the order of few seconds). While the Bitcoin payment verification scheme is designed to prevent double-spending, our results show that the system requires tens of minutes to verify a transaction and is therefore inappropriate for fast payments. An example of this use of Bitcoin was recently reported in the media: Bitcoins were used as a form of \emph{fast} payment in a local fast-food restaurant. Until now, the security of fast Bitcoin payments has not been studied. In this paper, we analyze the security of using Bitcoin for fast payments. We show that, unless appropriate detection techniques are integrated in the current Bitcoin implementation, double-spending attacks on fast payments succeed with overwhelming probability and can be mounted at low cost. We further show that the measures recommended by Bitcoin developers for the use of Bitcoin in fast payments are not always effective in detecting double-spending; we show that if those recommendations are integrated in future Bitcoin implementations, double-spending attacks on Bitcoin will still be possible. Finally, we propose and implement a modification to the existing Bitcoin implementation that ensures the detection of double-spending attacks against fast payments.
Kai-Min Chung, Huijia Lin, Rafael Pass
We present a constant-round concurrent zero-knowledge protocol for NP. Our protocol is sound against uniform polynomial-time attackers, and relies on the existence of families of collision-resistant hash functions, and a new (but in our eyes, natural) falsifiable intractability assumption: Roughly speaking, that Micaliâs non-interactive CS-proofs are sound for languages in P.
Vipul Goyal, Chen-Kuei Lee, Rafail Ostrovsky, Ivan Visconti
We propose the first black-box construction of non-malleable commitments according to the standard notion of non-malleability with respect to commitment. Our construction additionally only requires a constant number of rounds and is based only on (black-box use of) one-way functions. Prior to our work, no black-box construction of non-malleable commitments was known (except for relaxed notions of security) in any (polynomial) number of rounds based on any cryptographic assumption. This closes the wide gap existent between black-box and non-black-box constructions for the problem of non-malleable commitments. Our construction relies on (and can be seen as a generalization of) the recent non-malleable commitment scheme of Goyal (STOC 2011). We also show how to get black-box constructions for a host of other cryptographic primitives. We extend our construction to get constant-round concurrent non-malleable commitments, constant-round multi-party coin tossing, and non-malleable statistically hiding commitments (satisfying the notion of non-malleability with respect to opening). All of the mentioned results make only a black-box use of one-way functions. Our primary technical contribution is a novel way of implementing the proof of consistency typically required in the constructions of non-malleable commitments (and other related primitives). We do this by relying on ideas from the ``zero-knowledge from secure multi-party computation" paradigm of Ishai, Kushilevitz, Ostrovsky, and Sahai (STOC 2007). We extend in a novel way this ``computation in the head" paradigm (which can be though of as bringing powerful error-correcting codes into purely computational setting). To construct a non-malleable commitment scheme, we apply our computation in the head techniques to the recent (constant-round) construction of Goyal. Along the way, we also present a simplification of the construction of Goyal where a part of the protocol is implemented in an information theoretic manner. Such a simplification is crucial for getting a black-box construction. This is done by making use of pair wise-independent hash functions and strong randomness extractors. We show that our techniques have multiple applications, as elaborated in the paper. Hence, we believe our techniques might be useful in other settings in future.
Amit Sahai
One of the most fundamental goals in cryptography is to design protocols that remain secure when adversarial participants can engage in arbitrary malicious behavior. In 1986, Goldreich, Micali, and Wigderson presented a powerful paradigm for designing such protocols: their approach reduced the task of designing secure protocols to designing protocols that only guarantee security against âhonest-but-curiousâ participants. By making use of zero-knowledge proofs, the GMW paradigm enforces honest behavior without compromising secrecy. Over the past two decades, this approach has been the dominant paradigm for cryptographic protocol design, based on zero-knowledge protocols based on computational hardness assumptions. In this work, we describe a new general paradigm/protocol compiler for secure protocol design known as the IPS compiler, that departs considerably from the GMW framework, and provides a method for obtaining efficient protocols with information-theoretic security guarantees in settings where appropriate channels exist. This new approach also reduces the task of designing secure protocols to designing protocols that only guarantee security against honest-but-curious participants. However, the new approach avoids the use of zero-knowledge proofs, and instead makes use of multi-party protocols in a much simpler setting - where the majority of participants are completely honest (such multi-party protocols can exist with information-theoretic security guarantees without assuming any special channels). The IPS paradigm yields protocols that rely on Oblivious Transfer channels (OT) as a building block. This offers a number of advantages in generality and efficiency. In contrast to the GMW paradigm, by avoiding the use of zero-knowledge proofs, the IPS paradigm is able to treat all of its building blocks as âblack boxesâ. This allows improvement over previous results in the area of secure computation. In particular, the IPS compiler yields conceptually simpler and more efficient ways for basing unconditionally secure cryptography on OT and other noisy channels; more efficient protocols for generating a large number of OTs using a small number of OTs; and secure and efficient protocols which only make a blackbox use of cryptographic primitives or underlying algebraic structures in settings where no such protocols were known before.
Yan Zhu, Shanbiao Wang, Hongxin Hu, GailâJoon Ahn ¡ 5 authors
A hybrid cloud is a cloud computing environment in which an organization provides and manages some internal resources and has others provided externally. However, this new environment could bring irretrievable losses to the clients due to a lack of integrity verification mechanism for distributed data outsourcing. To support scalable service and data migration, in this paper we address the construction of a collaborative integrity verification mechanism in hybrid clouds where we consider the existence of multiple cloud service providers to collaboratively store and maintain the clients' data. We propose a collaborative provable data possession scheme adopting the techniques of homomorphic verifiable responses and hash index hierarchy. In addition, we articulate the performance optimization mechanisms for our scheme and prove the security of our scheme based on multi-prover zero-knowledge proof system, which can satisfy the properties of completeness, knowledge soundness, and zero-knowledge. Our experiments also show that our proposed solution only incurs a small constant amount of communications overhead.
Jinguang Han, Willy Susilo, Yi Mu, Jun Yan
No abstract is available for this record.
Nan Guo, Tianhan Gao, Bin Zhang
It is important that during the execution of a business process built from composable Web services from multiple domains, the component service be able to verify the identity of the user to check it has the required permissions for accessing the services, while at the same time identity attributes need to be protected properly as they can be target of attacks. In such context, we propose a privacy-preserved multi-domain identity attributes verification model BPVrfy. It extends federate identity management with support for multiple identity verification policies and privacy enhancement. Identity attributes verification process is partitioned into three sub-procedures consisting of attribute provision, federation enrollment and attributes transfer, and then a series of protocols based on cryptographic schemes is proposed respectively. BPVrfy adopts Perdersen Commitment, Zero-Knowledge Proof of Knowledge, BGLS Aggregate Signature and Certificate-Based Signature (CBS) cryptographic schemes together to give a privacy-preserved federate identity attributes verification solution for multi-domain Web services-based business processes.
Salil Vadhan, Shafi Goldwasser
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 1999.
Reza Sepahi, Ron Steinfeld, Josef Pieprzyk
No abstract is available for this record.
Qian Zhang, De Han
In this paper, through introducing the Williams public-key cryptosystem in detail, the analysis of the characteristics of the system, and the combination with zero knowledge proof, we set up a zero-knowledge proof scheme based on Williams public-key cryptosystem. The scheme will enrich the theory of cryptography, and particularly zero-knowledge proof theory.