Optimistic Fair Exchange Using Trusted Devices

Dashti, Mohammad Torabi

doi:10.1007/978-3-642-05118-0_49

Cited by 4 publications

(4 citation statements)

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“…Some authors [19,[21][22][23][24][25][26][27][28][29][30][31] used definitions that fit the definition we have called hard-timeliness. While other authors [8,9,13,15,[32][33][34][35][36][37][38][39][40][41][42][43][44][45] used definitions that fit the definition we have called soft-timeliness. Some introduced nuance: predetermined time [34,37], agreed time [35,36], bounded time [39], or that the protocol defines a deadline [45].…”

Section: Timelinessmentioning

confidence: 99%

A Hard-Timeliness Blockchain-Based Contract Signing Protocol

Ferrer-Gomila,

Hinarejos

2023

Computers

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In this article, we present the first proposal for contract signing based on blockchain that meets the requirements of fairness, hard-timeliness, and bc-optimism. The proposal, thanks to the use of blockchain, does not require the use of trusted third parties (TTPs), thus avoiding a point of failure and the problem of signatories having to agree on a TTP that is trusted by both. The presented protocol is fair because it is designed such that no honest signatory can be placed at a disadvantage. It meets the hard-timeliness requirement because both signatories can end the execution of the protocol at any time they wish. Finally, the proposal is bc-optimistic because blockchain functions are only executed in case of exception (and not in each execution of the protocol), with consequent savings when working with public blockchains. No previous proposal simultaneously met these three requirements. In addition to the above, this article clarifies the concept of timeliness, which previously has been defined in a confusing way (starting with the authors who used the term for the first time). We conducted a security review that allowed us to verify that our proposal meets the desired requirements. Furthermore, we provide the specifications of a smart contract designed for the Ethereum blockchain family and verified the economic feasibility of the proposal, ensuring it can be aligned with the financial requirements of different scenarios.

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Section: Timelinessmentioning

confidence: 99%

A Hard-Timeliness Blockchain-Based Contract Signing Protocol

Ferrer-Gomila,

Hinarejos

2023

Computers

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“…These are used for exchanging idempotent items as well, mainly in order to increase protocols' efficiency or flexibility. Examples are [Tor09] to reduce the number of messages to three in the optimistic sub-protocol, [VPG01] for exchanging time-sensitive items, and [TMH06] for optimistic exchange of non-revocable, non-generatable items; recall that optimistic FE requires that at least one of the items be either revocable or generatable [SW02]. 11 See also [AV04, AGGV05, ES05, FFD + 06, GR06] on using trusted devices in FE.…”

Section: A Selective Literature Reviewmentioning

confidence: 99%

“…Fair exchange between trusted devices requires three messages in the optimistic protocol when the items subject to exchange are idempotent [Tor09]. For exchanging non-idempotent items three messages in the optimistic sub-protocol are sufficient, given that the trusted devices have access to an unlimited secure storage; otherwise, four messages in the optimistic sub-protocol are sufficient and necessary [Tor09].…”

Section: A Selective Literature Reviewmentioning

confidence: 99%

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Handbook of Financial Cryptography and Security

Rosenberg¹

2010

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Alice to her destination before she pays. The fee is 100 Euros. Alice rips a 100 Euro bill into halves, and gives a half to Bob. To receive the other half, it is now in Bob's interest to take Alice to her destination. Alice, however, has already "spent" her 100 Euros, and does not benefit from not giving the other half to Bob, once Bob takes her to her destination. Do these scenarios describe fair interactions? We will analyze them more carefully in the following. In the cut and choose scenario, indeed there is an assumption that neither Alice nor Bob would take the whole cake and simply run away. Under this assumption, cut and choose is fair, in the sense that Alice and Bob will both be content with the result. None of them has any reason to envy the other one, cf. [BPW07].In the taxi driver scenario, clearly Bob should take Alice to her destination to get paid. Bob, however, knows that Alice has no interest in not paying him. She has already ripped up her 100 Euro bill, and can as well give the other half to Bob, once she is at her destination. 1 Here, Bob relying on the assumption that Alice is rational would take Alice to her destination. Similarly, Alice under the assumption that Bob is rational would rip up the 100 Euro bill. Remark that both parties need to assume that their opponent is rational in this scenario. Indeed, a malicious Alice could harm Bob by not paying him the other half, and a malicious Bob could harm Alice by not taking her to her destination after she has ripped the bill.Note that no such rationality assumption is needed to ensure fairness in the cut and choose scenario. If Alice cuts the cake unfairly, it is only Alice who is in a disadvantage. In other words, both Alice and Bob are guaranteed to end up with at least half of the cake, without any assumptions on the rationality of the other party; Alice however must play rational to ensure that she gets at least a half.These examples show that fairness is indeed a subtle issue. In the following, we abstract away various non-technical aspects of fairness, and focus on fairness in electronic exchanges. Fairness in electronic exchangesAt a high level of abstraction, an action, such as signing a contract, may be considered as a single event even though it is made up of a number of more elementary actions. We say that the execution of such a composed action is atomic if either all of its sub-actions are executed, or none at all.Applying this terminology to electronic exchanges, we understand fairness as the basic property of atomicity, meaning that all parties involved in the interaction receive a desired item in exchange for their own, or none of them does so. The exchange of items is often governed by a set of rules, stating which steps are taken in which order and by whom. Such a set of rules is referred to as a protocol. Fairness here is thus a property of the means of the exchange, e.g. a protocol, rather than the exchanged material per se.The difference between electronic exchange and conventional commerce and barter essentially lies in ...

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