Legally Fair Contract Signing Without Keystones

Abstract

Abstract. In two-party computation, achieving both fairness and guaranteed output delivery is well known to be impossible. Despite this limitation, many approaches provide solutions of practical interest by weakening somewhat the fairness requirement. Such approaches fall roughly in three categories: "gradual release" schemes assume that the aggrieved party can eventually reconstruct the missing information; "optimistic schemes" assume a trusted third party arbitrator that can restore fairness in case of litigation; and "concurrent" or "legally fair" schemes in which a breach of fairness is compensated by the aggrieved party having a digitally signed cheque from the other party (called the keystone). In this paper we describe and analyse a new contract signing paradigm that doesn't require keystones to achieve legal fairness, and give a concrete construction based on Schnorr signatures which is compatible with standard Schnorr signatures and provably secure.

Multi-Party Electronic Contract Signing Protocol Based on Blockchain

“…Copyright c 2022 The Institute of Electronics, Information and Communication Engineers based on the blockchain from the legally fair contract signing technology without keystones [8]. In our MECS protocol, each contract participant needs to upload his or her own identity information, public key and signature to the blockchain, and use the aggregation verification algorithm to verify the signatures of other participants.…”

“…Also, an effective method resisting this attack was proposed by Wang et al [19] so that the improved scheme was truly perfect for concurrent signature. The legal and fair contract signature scheme (without keystone) [8] proposed by Ferradi et al can complete the exchange of signatures between two parties without keystone, which guarantees legal fairness and no abuse. However, this scheme requires multiple interactions between two parties, which poses security risks.…”

“…In [8], Ferradi et al put forward a contract signing paradigm based on the Schnorr signature, which does not need keystones to achieve legal fairness. As recalled in Fig.…”

“…• NTO: A notary office is a trusted entity for generating public parameters that need to be uploaded to the Fig. 1 The legally fair signature without keystones [8].…”

Delegate contract signing mechanism based on smart contract

“…Zhai et al proposed a new low-storage trusted third party and a non-abuse contract signing agreement to solve the problem of ensuring that the contract signing agreement is free from abuse and efficiency [36]. Ferradi et al proposed a new contract signing paradigm that does not need a cornerstone to achieve legal fairness, so as to solve the problem of achieving fairness and ensuring output delivery in contract signing [37].…”