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In this paper, we provide the first committed signature provably secure in the standard complexity model based on the strong RSA assumption. The idea behind the construction is that given any valid partial signature of message m, if a co-signer with its auxiliary input is able to generate variables called the resolution of message m such that the distribution of the variables is indistinguishable...
In this paper we address video-on-demand (VOD) scenarios. Initially, we discuss how previous results on the unsuitability of the current adopted business model for the e-commerce of digital items affects VOD services. Then, we propose a reversible degradation method in order to address the lack of an accurate item validation step in current e-commerce implementations, thus providing robustness against...
We study the automatic synthesis of fair non-repudiation protocols, a class of fair exchange protocols, used for digital contract signing. First, we show how to specify the objectives of the participating agents and the trusted third party as path formulas in linear temporal logic and prove that the satisfaction of these objectives imply fairness; a property required of fair exchange protocols. We...
A non-repudiation protocol aims to provide non-repudiation service. Non-repudiation service, one of the essential security services in computer networks, protects the parties involved in a transaction against the other party denying that a particular event or action took place. Non-repudiation protocols are a special type of fair exchange protocols, and fairness is a key property that must be respected...
First we revisit three (BGLS, MBGLS and GZZ) verifiably encrypted signature schemes. We find that they are all not strong unforgeable. We remark that the notion of existential unforgeable is not sufficient for fair exchange protocols in most circumstances. So we propose three new (NBGLS, MBGLS and NGZZ) verifiably encrypted signature schemes which are strong unforgeable. Also we reconsider other two...
Fair exchange protocols have been studied intensively in recent years. But a lot of methods are still performed manually. In this paper an automatic method is proposed for analyzing fair exchange protocols. In this method we formalize security properties of fairness and non-repudiation in TLA (temporal logic of action) and define common predicates to make the analysis automatic. An "end"...
A new optimistic fair exchange protocol between a customer (C) and a merchant (M) is presented in this paper. It makes use of trusted third party (TTP) but its use is kept to minimum when disputes arise. The protocol is for exchanging a payment with a digital product such as software. A new idea, in which if the parties are willing to exchange then they are enforced to be honest, is originated in...
In this paper we present an attack on a fair exchange protocol proposed by Wu and Varadharajan. We show that, after two executions of the protocol, a dishonest participant can collect enough information in order to obtain some secret information of the other participant. This precisely allows him to compute the final signature of the other participant in all subsequent executions of the protocol,...
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