Based on the improved perfect concurrent signature,this paper proposed an abuse-free fair exchange protocol without trusted third party.This protocol avoided the flaw,by which buyer could prove to others that he has done an artificial trade with the shop,existed in other fair exchange protocols based on perfect concurrent signature.In the proposed protocol,buyer and shop bound the order information,payment information,and digital content together in the ambiguity signature which could be verified publicly after the buyer released extra keystones.And the buyer could get the key from the shop to decrypt the cipher of the digital content he wanted after he released keystones.The keystones bound the ambiguity signature,deal information of the buyer and shop together to avoid any one of the signer abuse these information.This protocol could be used in P2P network in which it's hard to find a trusted third party.Also using this protocol could avoid the risk that third party cooperating with one party to cheat others and avoid the performance bottleneck caused by third party.
Based on the improved perfect concurrent signature,this paper proposed an abuse-free fair exchange protocol without trusted third party.This protocol avoided the flaw,by which buyer could prove to others that he has done an artificial trade with the shop,existed in other fair exchange protocols based on perfect concurrent signature.In the proposed protocol,buyer and shop bound the order information,payment information,and digital content together in the ambiguity signature which could be verified publicly after the buyer released extra keystones.And the buyer could get the key from the shop to decrypt the cipher of the digital content he wanted after he released keystones.The keystones bound the ambiguity signature,deal information of the buyer and shop together to avoid any one of the signer abuse these information.This protocol could be used in P2P network in which it's hard to find a trusted third party.Also using this protocol could avoid the risk that third party cooperating with one party to cheat others and avoid the performance bottleneck caused by third party.
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.
Concurrent signature provided a novel idea for fair exchange protocol without trusted third party. Perfect Concurrent Signature is proposed to strengthen the ambiguity of the concurrent signature. Wang et al, pointed out there exist an attack against the fairness of Perfect Concurrent Signature and proposed the improved perfect concurrent signature. This paper find that in proposed (perfect) concurrent signature protocol, no matter two party or multi-party, the signer could bind multiple messages with one keystone set but let the other signers know only one of the messages. Based on this observation, this paper proposes that accountability should be one of the security properties of (perfect) concurrent signature and we give the definition of accountability of concurrent signature. To illustrate this idea, this paper give an attack scene against the accountability of improved perfect concurrent signature proposed by Wang et al. Finally, this paper proposes an update version of perfect concurrent signature to avoid such attack.
A fair contract-signing protocol allows two potentially mistrusted parities to exchange their commitments (i.e., digital signatures) to an agreed contract over the Internet in afairway, so that either each of them obtains the other's signature, or neither party does. Based on the RSA signature scheme, a new digital contract-signing protocol is proposed in this paper. Like the existing RSA-based solutions for the same problem, our protocol is not only fair, but also optimistic, since the trusted third party is involved only in the situations where one party is cheating or the communication channel is interrupted. Furthermore, the proposed protocol satisfies a new property-abuse-freeness. That is, if the protocol is executed unsuccessfully, none of the two parties can show the validity of intermediate results to others. Technical details are provided to analyze the security and performance of the proposed protocol. In summary, we present the first abuse-free fair contract-signing protocol based on the RSA signature, and show that it is both secure and efficient.
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.
We present protocols for fair exchange of electronic data (digital signatures, payment and confidential data) between two parties A and B. Novel properties of the proposed protocols include: 1) offline trusted third party (TTP), i.e., TTP does not take part in the exchange unless one of the parties behaves improperly; 2) only three message exchanges are required in the normal situation; 3) true fair exchange, i.e., either A and B obtain each other's data or no party receives anything useful; no loss can be incurred to a party no matter how maliciously the other party behaves during the exchange. This last property is in contrast to previously proposed protocols with offline TTP ([1] and [21]), where a misbehaving party may get another party's data while refusing to send his document to the other party, and the TTP can provide affidavits attesting to what happened during the exchange. To our knowledge, the protocols presented here are the first exchange protocols which use offline TTP and at the same time guarantee true fair exchange of digital messages. We introduce a novel cryptographic primitive, called the Certificate of Encrypted Message Being a Signature (CEMBS), as the basic building block of the fair exchange protocols. It is used to prove that an encrypted message is a certain party's signature on a public file, without revealing the signature. We also give two examples to show in detail how the certificate can be constructed.
Customers are usually passive in an electronic commerce transaction. Based on a new two times concurrent signature, this article presents a fair electronic payment (E-payment) protocol. It can protect both of the participants' profits. Whatpsilas more, in this protocol customers have more initiative, and they can terminate the transaction before possible cheats (while they also should be responsible for the quit), so their security is enhanced. As there is no traditional trusted third party (TTP) in our scheme, network congestion and conspiracy problem can be avoided. Moreover, the protocol satisfies fairness and non-repudiation, and it can also be applied in the digital signature or product exchange process.