Llorenç Huguet Rotger

An Efficient Protocol for Certified Electronic Mail

Certified electronic mail is a kind of fair exchange of values: a message for a receipt. An exchange is fair if at the end of the exchange, either each party receives the item it expects or neither party receives any useful information about the others item. Fairness can be achieved through the involvement of a trusted third party (TTP). It is very interesting (and practical) the optimistic approach of involving a third party only in the case of exceptions: one party cannot obtain the expected item from the other party. Previous solutions using this approach implicitly assumed that players had reliable communication channels to the third party [2]. In this paper, we present an efficient (only three steps, the minimum), optimistic and fair protocol for certified electronic mail.

Efficient Optimistic N-Party Contract Signing Protocol

Contract signing is a fundamental service in the environment of the electronic commerce. It is a kind of fair exchange of values: a signature on a text contract for another signature on the same text. We present a fair protocol that requires the existence and possible involvement of a TTP (trusted third party), but it only intervenes in case of exception (it plays a subsidiary role). The protocol is the best solution to the date in terms of efficiency. We present and analyse a two-party and three-party version of the protocol, and we outline an N-party version. Finally, it is very simple and easy to understand. If we think that at the end some conflicts will be solved in courts, it is a non worthless characteristic.

A Realistic Protocol for Multi-party Certified Electronic Mail

In some cases, users need to notify the same information to multiple recipients, with the requirement that these recipients have to send an acknowledgement of receipt. In this paper we present an optimistic protocol for multi-party certified electronic mail. A Trusted Third Party (TTP) can take part in a protocol run, but only in case of exception. Fairness is guaranteed for all parties being involved in a transaction. At the end of a protocol run, every party possesses enough evidence to prove the final state of the exchange. Parties can contact the TTP when they want (without temporal constraints). The presented protocol is the best one in terms of efficiency: only three steps have to be followed in the exchange sub-protocol.

Solving bao's colluding attack in wang's fair payment protocol

An electronic purchase is an essential operation of electronic commerce Fairness in the exchange of money and product, as well as anonymity of the buyer, are desirable features In Asiacrypt 2003, C.H Wang [8] presented a purchase protocol satisfying both anonymity and fairness, adapting the anonymous payment system of Brands [2], using a restrictive confirmation signature scheme Later, In Asiacrypt 2004, Feng Bao [1] demonstrated that Wangs protocol [8] can be vulnerable to attacks produced by colluding users, and he affirmed that the protocol cannot be corrected due to the anonymity of the protocol We will show that it is possible to correct Wangs protocol in order to avoid colluding attacks We present a solution that modifies slightly the original protocol, maintaining the anonymity and untraceability of the original version Finally, we discuss the convenience to achieve the property of timeliness.

A Juridical Validation of a Contract Signing Protocol

Electronic contracting is an essential service to develop electronic commerce. But this service is not very used because merchants and consumers do not trust in contracting by electronic means. For time we already have technical solutions that should allow to give trust to the actors implied in this new scenario. But the lack of international standards and of an appropriate juridical mark, suppose a serious restraint to the contracting by electronic means. Well then, in recent years we can observe some legislative initiatives in the European Union to give full juridical effect to electronic contracting. With these two elements already in course, we believe that a last step will be necessary: to assess the adaptation of the technical solutions regarding the enacted legislation. In this paper, juridical and technical analysis of contract signing protocols is carried out. Besides, we present a modified version of a previous optimistic fair protocol for contract signing.