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IEE Proceedings - Communications

Signature-based approach to fair document exchange

Qi Shi, N. Zhang, M. Merabti

Published Jan 1, 2003• 12 citations
Publisher

Abstract

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.

DOI
10.1049/ip-com:20030306

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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.
This work presents a novel protocol for fair exchange of DSA-based signatures to support an e-commerce activity of digital contract signing. The protocol employs an off-line semitrusted third party (STTP), which participates in the protocol execution only in exceptional circumstances and which involvement in the protocol is transparent. The protocol can tolerate the STTP's own misbehaviour (i.e. if it does not collude with other participants of the protocol) and it prevents the STTP from gaining the exchanged signatures or the signed document. The protocol is based on the principle of verifiable and recoverable signature encryption, and in comparison with related protocols is more efficient.
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.
In this paper, a new fair certified email protocol is proposed. The proposed protocol uses offline trusted third party (TTP) that will only be involved if a party misbehaves, otherwise the TTP is inactive. The protocol is based on the verifiable and recoverable encryption of keys. In this regard, the recipient of an email will be able to verify if the encrypted key used to encrypt the email is correct. The protocol comprises of only three messages in the exchange sub-protocol and three messages in the recovery sub-protocol. The proposed protocol is more efficient compared with related protocols.
One of the essential security services needed to safeguard online transactions is fair exchange. In fair exchange protocols two parties can exchange their signatures in a fair manner, so that either each party gain the other's signature or no one obtain anything useful. This paper examines security solutions for achieving fair exchange. It proposes new security protocols based on the "Certified Encrypted Message Being Signature" (CEMBS) by using RSA signature scheme. This protocol relies on the help of an "off-line Semi-Trusted Third Party" (STTP) to achieve fairness. They provide with confidential protection from the STTP for the exchanged items by limiting the role and power of the STTP. Three different protocols have been proposed. In the first protocol, the two main parties exchange their signatures on a common message. In the second protocol, the signatures are exchanged on two different messages. While in the third one, the exchange is between confidential data and signature.
Based on the verifiably encrypted signature scheme without random oracles recently proposed by Gorantla et al.,a new scheme of optimistic fair exchange of digital signatures is proposed in this paper.The two players firstly exchange their verifiably encrypted signature on agreed-upon messages then their ordinary signature after the verification of each other's verifiably encrypted signature.If one of them executes the protocol dishonestly,the other can resort to a trusted third party so as to get the purpose of fair exchange of signatures.The proposed scheme has properties of short signature,low computation and verification cost.It can realize exchange of digital signatures fairly and efficiently.