Fair exchange in E-commerce

Many business transactions over the Internet involve the exchange of digital products between two parties - electronic mails, digital audio and video, electronic contract signing and digital signatures, to name a few. Often these transactions occur between players that do not trust each other. To facilitate such transactions, a number of secure protocols have been proposed. The main objective of these protocols is: either both the parties obtain each other's items or none do. Sometimes it is not possible to meet the above objective and researchers have aimed for a weaker objective: gather evidence during protocol execution using which an honest party can prove his case. Protocols which meet any of the two objectives are collectively termed fair exchange protocols. In this paper we review some of the work done on such fair exchange protocols and identify areas that still need to be addressed.