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Journal of Communications

Signcryption-based fair exchange protocol

Yingyou Wen

Published Jan 1, 2010• 3 citations
OpenAlex

Abstract

By introducing signcryption technology into concurrent signature,a signcryption-based concurrent signature scheme was presented,which was proven to have the existential unforgeability against adaptive chosen messages attacks under the random oracle model,Based on this scheme,a fair exchange protocol was proposed,which could be used to exchange digital goods.This protocol did not need secure communications channel,in which two parties generate sym-metrical ambiguous signatures and individual keystones were released by themselves,which ensured the properties of confidentiality,ambiguousness and fairness,which made our protocol could be used in e-commerce payment,e-contract signing,mail authentication,etc.

Related papers

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Perfect concurrent signature was introduced as an efficient approach to solving the problem of fair exchange of signatures. Almost all fair exchange e-commerce protocols that have been proposed until now either do not provide message privacy protection or adopt the sign-then-encrypt scheme to provide confidentiality. However, confidentiality is an important requirement of e-commerce protocols. This paper proposed a new concept called perfect concurrent signcryption which combined the concepts of perfect concurrent signature and signcryption together to resolve the confidentiality problem in e-commerce systems. It also proposed a certificateless perfect concurrent signcryption scheme and proved its security in the random oracle model. The scheme published the two ambiguous signcryptions in any order. Compared with the sign-then-encrypt scheme, this scheme enjoys shorter message length and less operation cost, which makes the scheme has wide application prospects.

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Through analysis, we point out Luo et al.’s and Sun et al.’s signcryption-based concurrent signature schemes have the same defect in ambiguity and therefore the fair exchange protocols based on their schemes are not fair. Thus based on the notions of signcryption and concurrent signature, a new signcryption-based concurrent signature scheme from bilinear pairing is presented, and based on this scheme, a new fair exchange protocol is proposed. Since we adopt a new method to construct the new signcryption-based concurrent signature scheme, the new scheme redresses the flaw of Luo et al.’s and Sun et al.’s schemes, and the fair exchange protocol based on the new scheme is also fair. Besides, due to the new scheme’s independence of the ring signature and simplification of encryption operations, the new scheme has the advantage of short signatures and low computation cost. We improve Luo et al.’s definition of the security model of a signcryption-based concurrent signature scheme and prove the proposed scheme and protocol are secure under the computational Diffie-Hellman assumption in the random oracle model.

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•Jan 1, 2014•0 citations

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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.

Wuhan University Journal of Natural Sciences•Nov 1, 2006•3 citations
By introducing signcryption technology into concurrent signature,a signcryption-based concurrent signature scheme was presented,which was proven to have the existential unforgeability against adaptive chosen messages attacks under the random oracle model,Based on this scheme,a fair exchange protocol was proposed,which could be used to exchange digital goods.This protocol did not need secure communications channel,in which two parties generate sym-metrical ambiguous signatures and individual keystones were released by themselves,which ensured the properties of confidentiality,ambiguousness and fairness,which made our protocol could be used in e-commerce payment,e-contract signing,mail authentication,etc.
Perfect concurrent signature was introduced as an efficient approach to solving the problem of fair exchange of signatures. Almost all fair exchange e-commerce protocols that have been proposed until now either do not provide message privacy protection or adopt the sign-then-encrypt scheme to provide confidentiality. However, confidentiality is an important requirement of e-commerce protocols. This paper proposed a new concept called perfect concurrent signcryption which combined the concepts of perfect concurrent signature and signcryption together to resolve the confidentiality problem in e-commerce systems. It also proposed a certificateless perfect concurrent signcryption scheme and proved its security in the random oracle model. The scheme published the two ambiguous signcryptions in any order. Compared with the sign-then-encrypt scheme, this scheme enjoys shorter message length and less operation cost, which makes the scheme has wide application prospects.
Through analysis, we point out Luo et al.’s and Sun et al.’s signcryption-based concurrent signature schemes have the same defect in ambiguity and therefore the fair exchange protocols based on their schemes are not fair. Thus based on the notions of signcryption and concurrent signature, a new signcryption-based concurrent signature scheme from bilinear pairing is presented, and based on this scheme, a new fair exchange protocol is proposed. Since we adopt a new method to construct the new signcryption-based concurrent signature scheme, the new scheme redresses the flaw of Luo et al.’s and Sun et al.’s schemes, and the fair exchange protocol based on the new scheme is also fair. Besides, due to the new scheme’s independence of the ring signature and simplification of encryption operations, the new scheme has the advantage of short signatures and low computation cost. We improve Luo et al.’s definition of the security model of a signcryption-based concurrent signature scheme and prove the proposed scheme and protocol are secure under the computational Diffie-Hellman assumption in the random oracle model.
ABSTRACT A 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 aim to allow two parties to exchange digital items in a fair manner. Optimistic fair exchange (OFE) is a kind of protocols that solves the fair exchange problem with the help of a trusted third party (TTP), usually referred to as an `arbitrator'. The participation of the arbitrator is only required when there is a dispute between the exchanging parties. In the literature, the highest level of security of optimistic fair exchange is the multi-user security in the chosen-key model, proposed by Huang, Yang, Wong and Susilo in CT-RSA 2008. They showed that an efficient optimistic fair exchange scheme, secure in this sense, can be constructed generically from a conventional signature and a ring signature. In particular, the underlying ring signature is required to be unforgeable under an adaptive attack, against a static adversary in the 2-user setting.\nConcurrent signatures, introduced by Chen, Kudla and Paterson in Eurocrypt 2004, allow two parties to produce two ambiguous signatures until an extra piece of information, the keystone, is released by one of the parties. Upon the release of the keystone, the ambiguity will be revoked and the signatures bind to their true signers concurrently. Concurrent signatures, however, are known to fall just short of fully solving the long standing fair exchange of signatures problem. The price for not requiring any TTP is that the party who holds the keystone always has an advantage over the other party in controlling when and whether the protocol completes or not.\nIn this thesis, the fair exchange of digital signatures problem is studied. In the first part of this thesis, the OFE security is strengthened and a more practical model which is called enhanced chosen-key model is proposed. Unlike the existing multiuser setting and chosen-key model, an adversary in the enhanced chosen-key model is further provided with the signing oracle that outputs full signatures generated by the signer, and may even be allowed to have access to the arbitrator's secret key. The necessity for the new model is demonstrated. It is shown that two existing methodologies for constructing optimistic fair exchange schemes remain valid in the enhanced chosen-key model.\nNext, the efficiency of OFE constructions is improved. A model for 2-user ring signatures called `unforgeability against restricted adaptive attacks' is proposed and it is shown that the new ring model is strictly weaker than the model of unforgeability under an adaptive attack, against a static adversary in the 2-user setting. Based on the finding that 2-user ring signatures secure in this weaker model will suffice to guarantee the security of the resulting OFE schemes in the enhanced chosenkey model, the most efficient OFE scheme whose security does not rely on random oracles is proposed.\nNew situations in OFE are also investigated, and the applications of OFE are extended. The scenarios where the digital items to be exchanged are threshold signatures are considered, and the notion of threshold-oriented OFE (TOFE) together with a security model and an efficient concrete scheme is proposed. It is identified that in some scenarios, it is required that prior to the completion of the protocol, no information about the actual exchange should be revealed to an outsider. To achieve this purpose, the notion of perfect ambiguous optimistic fair exchange (PAOFE) is introduced, the security model for PAOFE is proposed and a generic construction based on existing primitives is offered. OFE in the attribute-based setting is considered and the notion of attribute-based optimistic fair exchange (ABOFE) is proposed. The security model and a construction for ABOFE are presented as well.\nFinally, concurrent signatures is revisited. It is showed that theoretically the party who controls the keystone in a concurrent signature scheme has more advantages than previously thought. In particular, the notion is examined and the advantages are classified into three levels.It is demonstrated that concurrent signatures may be abused in practical applications if one fails to take these advantages into account.
Based on perfect concurrent signature, a novel fair exchange protocol was presented. In this protocol anyone can’t identify who has signed which signature when two parties have exchanged their two ambiguous signatures and rela- tive data items. Not until the initial signer publishes a secret information, are the two signatures bound to respective signer concurrently. After that, the other party sends the key of decrypting goods, and thus the two parties can fairly get each other’s data items without the trusted third party (TTP), which avoids the possibility of two parties’ collusion and the bottleneck of the TTP involvement. Through analysis, this protocol well ensures some significant properties of fair ex- change, such as fairness, non-repudiation and abuse-free etc. What’s more, it only needs four messages between two par- ties and it is very simple and highly efficient.
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.