Design And Analysis On Verifiably Encrypted Signature

With the explosive growth of internet, on-line business starts to be an attracting and promising channel for property-exchange in our daily lives. Ensuring a fair exchange among participants, which is to say that either each participant gets what he/she wants or neither dose, is vital for all kinds of on-line business:electronic checks, electronic airplane ticket, electronic contract signing, just to mention a few. But the behind-screen nature of internet makes on-line trading impossible to realize or simulate the real-life trading in a simultaneous fashion between the sellers and buyers. One simple solution is to introduce an on-line trust third-party (TTP) to manage the tradings, when participants wanted to make business with each other, they referred to the TTP by sending the property of their own to the TTP and TTP took the charge of distributing the properties. This kind of solution demands involvement of the TTP during each one of the tradings no matter how honest the participants are, which makes the TTP become the potential bottle-neck due to its process speed and bandwidth. So a off-line TTP in a fair exchagne is a more flexible and more attractive solution, and this kind of fair exchange with an off-line TTP is called optimistic fair exchange. And verifiably encrypted signature becomes the building block of optimistic fair exchange.This paper focuses on the design of new verifiably encrypted signature scheme and its related security analysis. And we discuss the general strategy of the design and the general method for proving the security. Our newly designed verifiably encrypted signature applies the general strategies into the dual system framework proposed by Waters recently, and we get a provable secure verifiably encrypted signature in standard model. And also we apply the general method for proving security to the security analysis of our new scheme. We further the security analysis to factor out the flaw in the opacity proof in Zhang et al.’s standard model verifiably encrypted signature and give a better opacity proof. The main contributions and innovations of this paper are as follows.1. General strategies for designing the verifiably encrypted signatures.2. Focusing on opacity and unforgeability of a verifiably encrypted signature scheme, we give a general method for security analysis.3. A new verifiably encrypted signature in standard model. Compared with other verifiably encrypted signature scheme, our new scheme applies the brandnew dual system framework, using simpler assumptions in standard model with public parameters of constant size. As far as we know, we are the first to apply the duel system to the design of verifiably encrypted signature. We divide the signature space into two types and prove that neither type of the signature could be forged or extracted by defining a sequence of games where we can change the query signatures from one type to another one by one without the notice of the adversary4. We give a new opacity proof for a secure verifiably encrypted signature scheme which has a flawed version of opacity proof.