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ACM SIGSAC Conference on Computer and Communications Security (CCS)

Fair exchange with a semi-trusted third party (extended abstract)

Matthew K. Franklin, Michael K. Reiter

Published Apr 1, 1997• 165 citations
Publisher

Abstract

We present new protocols for two parties to exchange documents with fairness, i.e., such that no party can gain an advantage by quitting prematurely or otherwise misbehaving.We use a third party that is L'semi-trusted", in the sense that it may misbehave on its own but will not conspire with either of the main parties.In our solutions, disruption by any one of the three parties will not allow the disrupter gain any useful new information about the documents.Our solutions are efficient and can be based on any of several cryptographic assumptions (e.g., factoring, discrete log, graph isomorpbism).We also discuss the application of our techniques to electronic commerce protocols to achieve fair payment.

DOI
10.1145/266420.266424

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Fair Exchange with a Semi-Trusted Third Party

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We present new protocols for two parties to exchange documents with fairness, i.e., such that no party can gain an advantage by quitting prematurely or otherwise misbehaving.We use a third party that is L'semi-trusted", in the sense that it may misbehave on its own but will not conspire with either of the main parties.In our solutions, disruption by any one of the three parties will not allow the disrupter gain any useful new information about the documents.Our solutions are efficient and can be based on any of several cryptographic assumptions (e.g., factoring, discrete log, graph isomorpbism).We also discuss the application of our techniques to electronic commerce protocols to achieve fair payment.
We present new protocols for two parties to exchange documents with fairness, i.e., such that no party can gain an advantage by quitting prematurely or otherwise misbehaving. We use a third party that is L‘semi-trusted”, in the sense that it may misbehave on its own but will not conspire with either of the main parties. In our solutions, disruption by any one of the three parties will not allow the disrupter gain any useful new information about the documents. Our solutions are efficient and can be based on any of several cryptographic assumptions (e.g., factoring, discrete log, graph isomorpbism). We also discuss the application of our techniques to electronic commerce protocols to achieve fair payment.
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.
The authors aim to present a protocol for fair document exchange between two parties, that incorporates a signature scheme based method for the recovery of a document decryption key. The principal idea for such key recovery is based on a verifiable and recoverable encryption of a key. This means that any party can verify the correctness of the key encrypted without actually viewing the key, and the party can be assured that a designated party can decrypt the encrypted key to recover the original key. A DSA (digital signature algorithm) is applied as an example to demonstrate how to implement such key encryption based on an off-line semi-trusted third party. The third party is off-line as they do not participate in an exchange in normal situations, and semi-trusted in the sense that they may misbehave but do not conspire with any party involved in the exchange. The main contribution of the paper is that it presents a fair document exchange protocol which is more efficient, simpler and easier to implement in comparison with related work.
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.