Many cryptographic protocols are intended to coordinate state changes among principals. Exchange protocols coordinate delivery of new values to the participants, e.g. additions to the set of values they possess. An exchange protocol is fair if it ensures that delivery of new values is balanced: If one participant obtains a new possession via the protocol, then all other participants will, too. ...

The contribution of this paper is threefold. First, we propose a novel specification of the fair exchange problem that clearly separates safety and liveness. This specification assumes a synchronous model where processes communicate by message passing and might behave maliciously. In this model, we prove a first impossibility related to the notion of trust, stating that no solution to fair exch...

In this paper we propose a new probabilistic Fair Exchange Protocol which requires no central Trusted Third Party. Instead, it relies on a virtually distributed and decentralized Trusted Third Party which is formalized as a Guardian Angel: a kind of Observer e.g. a tamper proof security device. We thus introduce a network model with Pirates and Guardian Angels which is well suited for Ad Hoc ne...

The concept of value is of great importance for investors. The goal of different groups of investors is always to maximize the value of their capital. The aim of this research is developing factors effective on securities in capital market in order to develop a paradigm for fair valuation that leads investors to make better decisions. To study fair value in a precise and comprehensive way, effe...

Optimistic contract signing protocols allow two parties to commit to a previously agreed upon contract, relying on a third party to abort or connrm the contract if needed. These protocols are relatively subtle, since there may be interactions between the subprotocols used for normal signing without the third party, aborting the protocol through the third party, or requesting connrmation from th...

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...

Certified mail is the fair exchange of a message for a receipt, i.e., the recipient gets the message if and only if the sender gets a receipt. It is an important primitive for electronic commerce and other atomicity services. Certified-mail protocols are known in the literature, but there was no rigorous definition yet, in particular for optimistic protocols and for many interleaved executions....

Security services become crucial to many applications such as e-commerce payment protocols, electronic contract signing, and certified e-mail delivery with the phenomenal growth of the Internet. For these applications fair exchange must be assured. A fair protocol allows two members participating in a contract to exchange digital signatures over the Internet in a fair way, so that either each p...