Flexible Anonymous Subscription Schemes

We propose a simple and efficient Subscription Scheme, allowing a set of users to anonymously pay for and request access to different services offered by a number of service providers. Using an e-cash system in such a scenario, the identity of the user would be hid into the e-coin in order to preserve its anonymity. Providing an additional triggering mechanism that opens this identity in case of double spending, also the service provider will be protected against fraud. Note that in traditional e-cash universality of the coin is required, however, in our scenario, the use of the token is completely determined at issuing time (yet this final aim remains hidden to the issuing authority). This allows for our construction, in which moreover fraud detection here implies no loss of anonymity; as we make access tokens independent of the owner in a quite simple and efficient way. On the other hand, if different usages of the same token are allowed, these are fully traceable by the service providers. An application to e-polling protocols is also given.