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Ecient Fair Exchange with Veriable Conrmation of Signatures

Liqun Chen

Published Jan 1, 1998• 2 citations
OpenAlex

Abstract

We propose a new ecient protocol, which allows a pair of potentially mistrusting parties to exchange digital signatures over the Internet in a fair way, such that after the protocol is running, either each party obtains the other's signature, or neither of them does. The pro- tocol relies on an o-line Trusted Third Party (TTP), which does not take part in the exchange unless any of the parties behaves improperly or other faults occur. Eciency of the protocol is achieved by using a cryptographic primitive, called conrmable signatures (or designated con- rmer signatures in its original proposal (9)). We recommend using a new ecient conrmable signature scheme in the proposed fair exchange pro- tocol. This scheme combines the family of discrete logarithm (DL) based signature algorithms and a zero-knowledge (ZK) proof on the equality of two DLs. The protocol has a practical level of performance: only a moderate number of communication rounds and ordinary signatures are required. The security of the protocol can be established from that of the underlying signature algorithms and that of the ZK proof used.

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We propose a new ecient protocol, which allows a pair of potentially mistrusting parties to exchange digital signatures over the Internet in a fair way, such that after the protocol is running, either each party obtains the other's signature, or neither of them does. The pro- tocol relies on an o-line Trusted Third Party (TTP), which does not take part in the exchange unless any of the parties behaves improperly or other faults occur. Eciency of the protocol is achieved by using a cryptographic primitive, called conrmable signatures (or designated con- rmer signatures in its original proposal (9)). We recommend using a new ecient conrmable signature scheme in the proposed fair exchange pro- tocol. This scheme combines the family of discrete logarithm (DL) based signature algorithms and a zero-knowledge (ZK) proof on the equality of two DLs. The protocol has a practical level of performance: only a moderate number of communication rounds and ordinary signatures are required. The security of the protocol can be established from that of the underlying signature algorithms and that of the ZK proof used.
we propose a new efficient protocol. which allows a pair of potentially mistrusting parties to exchange digital signatures over the Internet in a fair way. The protocol relies on an off-line Trusted Third Party (TTP). which does not take part in the exchange unless any of the parties behaves improperly or other faults occur. Efficiency of the protocol is achieved by using a cryptographic primitive, called designated confirmer signatures. The confirmer commitment schemes and ordinary signatures are combines to form the confirmer signatures. The security of the protocol is analyzed and the fairness of it is guaranteed.
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.
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.
Based on a short signature scheme and discrete logarithm problem,a new fair exchange protocol with the off-line semi-Trusted Third Party(TTP) is proposed.The off-line semi-TTP intervenes into the protocol in case of trouble,which makes the fair exchange optimistic.The off-line TTP need not be completely trusted,since it can get neither signature exchanged when disputation is solved.Because this protocol is based on short signature,which needs low storage and little communication,it can be used in low-bandwidth communication and low-storage environments.
A non-repudiation protocol enables the fair exchange of an electronic message and an irrefutable digital receipt between two mistrusting parties over the Internet. That is, at the end of any execution instance of such a protocol, either both parties obtain their expected items or neither party does . In this paper, we first argue that it is really meaningful in practice to exploit generic fair non-repudiation protocols with transparent off-line trusted third party (TTP). Namely, in those protocols, each involved party could use any secure digital signature algorithm to produce non-repudiation evidences; and the issued evidences are the same regardless of whether the TTP is involved or not. Then, we present such a fair non-repudiation protocol to overcome some limitations and shortcomings in previous schemes. Technical discussions are provided to show that our protocol is not only secure but also the most efficient solution, compared with existing non-repudiation protocols. In addition, some potential extensions are also pointed out.