Properties of secure transaction protocols

Abstract Communication protocols are the computational basis for distributed electronic commerce systems, and thus the properties of these protocols define the forms of commerce possible in electronic systems. Existing protocols used for electronic commerce focus primarily on security properties, including message integrity, privacy and non-repudiation, and on basic transaction properties, usually just atomicity; their structural properties are limited to supporting two-party transactions with fixed semantics. We believe that the properties provided by these protocols limit their use to simple forms of commerce. In this paper we define the properties we believe are necessary for electronic commerce protocols. These include the security properties of existing protocols, and extend the transactional properties to include isolation and causality. Causality is a new property for transactions. It allows the order of the messages in a completed transaction to be independently verified, and thus inferences can be made about causal relationship between messages. We also extend the structural properties to support scalability, layering and separation of roles. Scalable protocols allow several parties to join each transaction. Protocol layering enables arbitrary transaction semantics and greater system modularity. Separation of roles provides independent adjudication of disputes between transaction participants and allows the use of varied exchange media. We term a protocol with the above properties a secure transaction protocol. Lastly, we present a protocol that provides these properties. We believe that this protocol can be used to support more complex and extended forms of electronic commerce than existing protocols.