Constructing fair-exchange protocols for E-commerce via distributed computation of RSA signatures

ABSTRACTA fair exchange protocol allows two entities to exchange digital signatures over open networks in a fair way, so that either each entity obtains the other's signature or neither entity does. Fair exchange protocol plays an important role in electronic commerce in the case of exchanging digital contracts. In this paper, we propose a fair exchange protocol based on identity‐based verifiably encrypted signatures. Our protocol involves an offline trusted third party which is only required when one entity attempts to cheat or crashes. The underlining identity‐based verifiably encrypted signature scheme is proven secure under the computational Diffie–Hellman assumption and is the first identity‐based verifiably encrypted signature scheme provably secure against existential unforgeable under adaptive chosen message and identity attacks in the standard model. Copyright © 2012 John Wiley & Sons, Ltd.

Fair exchange protocols are among the most important cryptographic primitives in electronic commerce. A basic fair exchange protocol requires that two parties who want to exchange their digital items either receive what they have been promised, or lose nothing. Privacy of fair exchange requires that no one else (other than the two parties) learns anything about the items. Fairness and privacy have been considered as two distinct properties of an exchange protocol. In this paper, we show that subtle ways of leaking the exchange item to the third parties affect fairness in fair exchange protocols when the item is confidential. Our focus is on Fair-Swap, a recently proposed fair exchange protocol that uses a smart contract for dispute resolution, has proven security in UC (Universal Composability) framework, and provides privacy when both parties are honest. We demonstrate, however, that FairSwap’s dispute resolution protocol leaks information to the public and this leakage provides opportunities for the dishonest parties to influence the protocol’s fairness guarantee. We then propose an efficient privacy-enhanced version of Fair-Swap, prove its security and give an implementation and performance evaluation of our proposed system. Our privacy enhancement uses circuit randomization, and we prove its security and privacy in an extension of universal composability model for non-monolithic adversaries that would be of independent interest.

The security of multimedia's transmission on Internet is very important. In this paper we have discussed digital watermarking technology and the protocol of fair exchange. Then, the scheme of network manufacture products electronic trading based on fair exchange protocol and digital watermarking technology is presented in this paper. Experiments show that the scheme has the properties of fair exchanging and copyright protection, and it is a good scheme to solve security and fairness problems.

An optimistic fair exchange (OFE) protocol is an effective tool helping two parties exchange their digital items in an equitable way with assistance of a trusted third party, called arbitrator, who is only required if needed. In previous studies, fair exchange is usually carried out between individual parties. When fair exchange is carried out between two members from distinct groups, anonymity of the signer in a group could be necessary for achieving better privacy. In this paper, we consider optimistic fair exchange of ring signatures (OFERS), i.e. two members from two different groups can exchange their ring signatures in a fair way with ambiguous signers. Each user in these groups has its own public-private key pair and is able to sign a message on behalf of its own group anonymously. We first define the security model of OFERS in the multi-user setting under adaptive chosen message, chosen-key and chosen public-key attacks. Then, based on verifiably encrypted ring signatures (VERS) we construct a concrete scheme by combining the technologies of ring signatures, public-key encryption and proof of knowledge. Finally, we show that our OFERS solution is provably secure in our security model, and preserving signer-ambiguity of ring signatures. To the best of our knowledge, this is the first (formal) work on this topic.

Devising a fair-exchange protocol for digital goods has been an appealing line of research in the past decades. The Zero-Knowledge Contingent Payment (ZKCP) protocol first achieves fair exchange in a trustless manner with the aid of the Bitcoin network and zero-knowledge proofs. However, it incurs setup issues and substantial proving overhead, and has difficulties handling complicated validation of large-scale data. In this paper, we propose an improved solution ZKCPlus for practical and flexible fair exchange. ZKCPlus incorporates a new commit-and-prove non-interactive zero-knowledge (CP-NIZK) argument of knowledge under standard discrete logarithmic assumption, which is prover-efficient for data-parallel computations. With this argument we avoid the setup issues of ZKCP and reduce seller's proving overhead, more importantly enable the protocol to handle complicated data validations. We have implemented a prototype of ZKCPlus and built several applications atop it. We rework a ZKCP's classic application of trading sudoku solutions, and ZKCPlus achieves 21-67 times improvement in seller efficiency than ZKCP, with only milliseconds of setup time and 1 MB public parameters. In particular, our CP-NIZK argument shows an order of magnitude higher proving efficiency than the zkSNARK adopted by ZKCP. We also built a realistic application of trading trained CNN models. For a 3-layer CNN containing 8,620 parameters, it takes less than 1 second to prove and verify an inference computation, and also about 1 second to deliver the parameters, which is very promising for practical use.

In the fair exchange problem, mutually untrusting parties must securely exchange digital goods. A fair exchange protocol must ensure that no combination of cheating or failures will result in some goods being delivered but not others, and that all goods will be delivered in the absence of cheating and failures.This paper proposes two novel randomized protocols for solving fair exchange using simple trusted units. Both protocols have an optimal expected running time, completing in a constant (3) expected number of rounds. They also have optimal resilience. The first one tolerates any number of dishonest parties, as long as one is honest, while the second one, which assumes more agressive cheating and failures assumptions, tolerates up to a minority of dishonest parties.The key insight is similar to the idea underlying the code-division multiple access (CDMA) communication protocol: outwitting an adversary is much easier if participants share a common, secret pseudo-random number generator.

Fairness is one of the basic requirements of e-commerce protocols and applications. CEMBS is proved to be an important cryptographic building primitive in constructing fair exchange protocols. In this paper the drawbacks of existing CEMBS-implementing methods are analyzed. A new CEMBS-constructing method based on RSA signature is proposed, which is proved to be simple, efficient and secure. Afterwards, a fair exchange protocol is built using the newly constructed CEMBS. And the devised scheme in this paper is the first efficient CEMBS based on RSA signatures.

The optimistic approach of involving a third party only in the case of exceptions is a useful technique to build secure, yet practical fair exchange protocols. Previous solutions using this approach implicitly assumed that players had reliable communication channels to the third party. We present a set of optimistic fair exchange protocols which tolerate temporary failures in the communication channels to the third party. A central feature of the protocols is that either player can asynchronously and unilaterally bring a protocol run to completion.

In this paper we discuss the two security issues: non-repudiation and fairness in association with e-commerce applications. In particular, these issues are addressed in the context of electronic data exchange, which is one of the most commonly seen e-commerce applications. In detail, this paper gives a survey of the approaches to non-repudiation and fair electronic data exchange protocols. We additionally discuss the current technologies that propose solutions to these issues, and the emerging standards in the area of business data formats and protocols for the exchange of such data. Finally, we discuss the architecture layer at which to implement the protocols for non-repudiation and fair data exchange.

The multi-party exchange of valuable digital resources in P2P environment has some problem on resources certification and objects exchange.A decentralized fair multi-party exchange protocol was proposed.The protocol adopted cross-validation theory to identify recourses and solved the problem of the negotiation among multi-party exchanges in term of one-way release mechanism and the new one-way exchange mesh structure.Meanwhile,the protocol certificated its own fairness on the basis of right cross validation.

The paper presents applications for the weak protection of secrets in which weakness is not just acceptable but desirable. For one application, two versions of a lottery scheme are presented in which the result of the lottery is determined by the ticket numbers purchased, but no one can control the outcome or determine what it is until after the lottery closes. This is because the outcome is kept secret in a way that is breakable after a predictable amount of time and/or computation. Another presented application is a variant on fair exchange protocols that requires no trusted third party at all.

The fair exchange protocol is one of the most fundamental cryptographic tool in many security applications such as contract signing protocols, certified e-mail systems, and e-payment schemes. BLS short signature (due to Boneh, Lynn, and Shacham) is among the most popular cryptographic primitives in pairing-based cryptography. We propose a new fair exchange protocol which can be used to exchange BLS signatures. To the best of our knowledge, it is the first abuse-free optimistic fair exchange protocol based on the BLS signature. And we show that it is both secure and efficient.

An electronic contract signing protocol is a fair exchange protocol where the parties exchange their signature on a contract. Some contract signing protocols have been presented, and usually they come with an informal analysis. In this paper we use Colored Petri Nets to formally verify the fairness and the resistance to five previously described attacks of FPH contract signing protocol. We have modeled the protocol and the roles of the signers, a trusted third party, malicious signers as well as the role of an intruder. We have proven that the protocol is resistant to typical attacks. However, we have detected three cases where the protocol generates contradictory evidences. Finally, we have explained which should be the behavior of an arbiter to allow the resolution of these conflicting situations.Keywordscontract signing protocolColoured Petri Netsformal verification

We present a group signature scheme, based on the hardness of lattice problems, whose outputs are more than an order of magnitude smaller than the currently most efficient schemes in the literature. Since lattice-based schemes are also usually non-trivial to efficiently implement, we additionally provide the first experimental implementation of lattice-based group signatures demonstrating that our construction is indeed practical -- all operations take less than half a second on a standard laptop. A key component of our construction is a new zero-knowledge proof system for proving that a committed value belongs to a particular set of small size. The sets for which our proofs are applicable are exactly those that contain elements that remain stable under Galois automorphisms of the underlying cyclotomic number field of our lattice-based protocol. We believe that these proofs will find applications in other settings as well. The motivation of the new zero-knowledge proof in our construction is to allow the efficient use of the selectively-secure signature scheme (i.e. a signature scheme in which the adversary declares the forgery message before seeing the public key) of Agrawal et al. (Eurocrypt 2010) in constructions of lattice-based group signatures and other privacy protocols. For selectively-secure schemes to be meaningfully converted to standard signature schemes, it is crucial that the size of the message space is not too large. Using our zero-knowledge proofs, we can strategically pick small sets for which we can provide efficient zero-knowledge proofs of membership.

An exchange protocol is a protocol that allows two or more parties to exchange electronic information. Bao et al. proposed a multi-party fair exchange protocol based on an offline TTP. Participants in this protocol have to trust the initiator of the exchange in addition of the TTP. In this paper we present an improved optimistic multi-party fair exchange protocol in which participants do not have to trust anyone except for the TTP. Moreover, the communication overhead of our protocol is not increased.