Fair Exchange Of Digital Signatures Research Articles

A blockchain-based signature exchange protocol for metaverse

Electronic Commodity Trading has a pivotal role in our economic activities. In the literature, there is a classic problem called “Fair Exchange” which is fundamental to electronic commodity trading. It means the participants can receive the exchange item of the counterparty as they have agreed on before. Since the ownership of items online is often authorized by digital signatures, we focus on the problem of the fair exchange of digital signatures in this paper. As the concept of the Metaverse becomes popular recently, what we are concerned about is how the fair exchange will evolve in a metaverse. It is said that the metaverse is a vision of how the next generation of the internet will operate and the research for the fair exchange problem in it is essential for a wide range of applications like trading a (Non-fungible-token) NFT. Many cryptographic fair exchange protocols are proposed to deal with such a problem. However, most of them should rely on a Trusted Third Party (TTP) and the security is restricted by the TTP. The way the metaverse will work is still being defined. But it will probably provide users with a decentralized environment and a fair exchange protocol relying on a TTP seems unsuitable for it. Recently, researchers present some blockchain-based fair exchange protocols to get rid of or reduce the power of a TTP. But these blockchain-based protocols face new challenges. Firstly, cryptography pairing operations are often contained in such a TTP-free protocol and cost too much for the blockchain. Secondly, the player may hang for an unacceptably long time of the latency of the blockchain network. Thirdly, it is difficult to protect the privacy of the signatures while making the whole protocol verifiable at the same time. To bridge these research gaps, this paper presents a novel signature exchange protocol called DFSE which is decentralized, verifiable, efficient and autonomous. To give a real-world evaluation, we perform the experiment on the live test network of Ethereum and the results show that our protocol is feasible.

How to protect privacy in Optimistic Fair Exchange of digital signatures

How to sign an electronic contract online between two parties (say Alice and Bob) in a fair manner is an interesting problem, and has been extensively studied for a long time. Optimistic Fair Exchange (OFE) is an efficient solution to it, in which a semi-trusted third party, named the arbitrator, is responsible for resolving any dispute that may arise during an exchange between Alice and Bob. Recently, several variants of OFE, such as Ambiguous OFE (AOFE) and Perfect AOFE (PAOFE), have been introduced to protect the privacy of Alice and Bob. These primitives prevent any outsider from telling which parties are involved in an exchange of digital signatures before the exchange completes. However, in PAOFE, AOFE and all the existing works on OFE, the arbitrator can always learn the signer’s full signature at (or even before) the end of resolution, which is undesirable in some important applications, for example, signing a contract between two parties which do not want others to find out even when there is a dispute that needs resolution by the arbitrator.In this work, we introduce a new notion called Privacy-Preserving Optimistic Fair Exchange (P2OFE) for protecting the privacy of users, in which other than Alice and Bob, no one else including the arbitrator, can collect any evidence about an exchange between them even after the resolution of a dispute. We formally define P2OFE and present the corresponding security models and propose a concrete and efficient construction of P2OFE. We also discuss about several extensions about implementation. Our scheme is proved to be secure under the given security models based on the Strong Diffie–Helllman and Decision Linear assumptions without relying on the random oracle heuristic.

A time sequence protocol to achieve the effect of fair exchange without trusted third party

A fair exchange protocol allows two parties to exchange items in a fair way, such that either both parties obtain the other’s item or neither party does. In this paper, we propose a time sequence protocol for exchanging participants’ warrants without a trusted third party (TTP). Then, each participant is able to sign a proxy signature on behalf of its opponent. Owing to the proxy signature’s restriction, the scheme achieves the desired effect of fair exchange of digital signatures. Our scheme is based on a time sequence rather than computation, and can be realized without the use of a TTP, thus differing from the existing fair exchange schemes. Compared with a concurrent signature, the proposed scheme does not need to release a keystone to wake the signatures when they exchange information fairly. The only advantage to the initial party is that it has the right to determine whether the exchanged warrants are valid before a designated time. However, because of the properties of proxy signatures, the initial party ultimately derives no benefit from this advantage. After the designated time, there is no additional advantage to benefit the initial party.

Preserving Transparency and Accountability in Optimistic Fair Exchange of Digital Signatures

Optimistic fair exchange (OFE) protocols are useful tools for two participants to fairly exchange items with the aid of a third party who is only involved if needed. A widely accepted requirement is that the third party's involvement in the exchange must be transparent, to protect privacy and avoid bad publicity. At the same time, a dishonest third party would compromise the fairness of the exchange and the third party thus must be responsible for its behaviors. This is achieved in OFE protocols with another property called accountability. It is unfortunate that the accountability has never been formally studied in OFE since its introduction ten years ago. In this paper, we fill these gaps by giving the first complete definition of accountability in OFE where one of the exchanged items is a digital signature and a generic (also the first) design of OFE where transparency and accountability coexist.

An identity-based scheme of fair exchange of digital signatures

Fair exchange of digital signatures is an important tool for signing digital contracts, e-payment and other electronic commerce actions. An ID-based scheme of fair exchange of digital signature is proposed in this paper. The protocol relies on a trusted third party, but is “optimistic”, in that the third party is only needed in cases where one player attempts to cheat or simply crashes. The proposed scheme has properties of short signature, low computation and verification cost. It can realize exchange of digital signatures fairly and efficiently. A key feature of our scheme is that it is identity-based, which needs no certificates and has a simple key management. To our best knowledge, this is the first identity-based scheme of fair exchange of digital signatures.

Practical Implementations of a Non-disclosure Fair Contract Signing Protocol

Contract signing is a practical application of the fair exchange of digital signatures. This application used to be realized by directly adopting the results of the fair exchange of signatures, which do not completely meet the requirements of the signing of a secret contract. The assistance of a trusted third party (TTP) and some cryptographic technology are required to allow two parties to exchange their signatures through the network in a fair manner because these two parties potentially may be dishonest or mistrust each other. This paper presents a subtle method of preventing the off-line TTP from gaining the exchanged signature and the corresponding message when a dispute occurs between the two parties wherein the TTP is required to take part in the exchange procedure. An advanced concept, the non-disclosure property, is proposed in order to prevent a party from misusing evidence left during the exchange process. Two approaches, namely the secret divide method and the convertible signature are demonstrated. To satisfy the properties of the traditional paper-based contract signing, the technique of multi-signature scheme is used in the proposed protocols.

Optimistic fair exchange of digital signatures

We present a new protocol that allows two players to exchange digital signatures over the Internet in a fair way, so that either each player gets the other's signature, or neither player does. The obvious application is where the signatures represent items of value, for example, an electronic check or airline ticket. The protocol can also be adapted to exchange encrypted data. It relies on a trusted third party, but is optimistic, in that the third party is only needed in cases where one player crashes or attempts to cheat. A key feature of our protocol is that a player can always force a timely and fair termination, without the cooperation of the other player, even in a completely asynchronous network. A specialization of our protocol can be used for contract signing; this specialization is not only more efficient, but also has the important property that the third party can be held accountable for its actions: if it ever cheats, this can be detected and proven.