Multi-party fair exchange (MFE) and secure multi-party computation (fair SMPC) are under-studied fields of research, with practical importance. In particular, we consider MFE scenarios where at the end protocol, either every participant receives other participant’s item, or no anything. We analyze case a trusted third party (TTP) is optimistically available, although emphasize that trust put on...

To implement fair exchange of digital signatures, we need an efficient scheme to commit a digital signature safely to a specific receiver. To satisfy this security requirement in an efficient manner, we introduce a new variant of digital signature called conditional signature which is a specially interpreted signature on a message and a condition together. By imposing a signer-chosen condition ...

Fair exchange between two or more potentially mutually distrusted parties has been identified as an important issue in electronic commerce. However, the correctness (fairness) of the existing fair exchange protocols that use a Trusted Third Party (TTP) is based on the assumption that during an exchange there are no failures at any of the local systems involved in the exchange, which is too stro...

This paper reports on the on-going Fair Integrated Data Exchange Services (FIDES) project aimed at developing a security middleware solution to support e-commerce transactions and the provision of the important fair exchange and nonrepudiation security services. Fair exchange ensures that either both business parties participating in a transaction receive the exchanged valuable items or neither...

In an electronic commerce environment, the merchant and the customer are unlikely to trust each other. This problem has motivated researchers to propose fair-exchange protocols based on using an on-line trusted third party; the third party receives the items being exchanged from the customer and the merchant and then forwards it to the other party in a fair manner. However, the third party is a...

Secure two party computation (2PC) is a well-studied problem with many real world applications. Due to Cleve’s result on general impossibility of fairness, however, the state-of-the-art solutions only provide security with abort. We investigate fairness for 2PC in presence of a trusted Arbiter, in an optimistic setting where the Arbiter is not involved if the parties act fairly. Existing fair s...

We introduce game theory as a formal framework in which exchange protocols can be modeled and their properties can be studied. We use this framework to give a formal deenition for rational exchange relating it to the concept of Nash equilibrium in games. In addition, we study the relationship between rational exchange and fair exchange. We prove that fair exchange implies rational exchange, but...

Multi-party contract signing (MPCS) protocols allow a group of signers to exchange signatures on a predefined contract. Previous approaches considered either completely linear protocols or fully parallel broadcasting protocols. We introduce the new class of DAG MPCS protocols which combines parallel and linear execution and allows for parallelism even within a signer role. This generalization i...