Proxy Signatures Secure Against Proxy Key Exposure

We provide an enhanced security model for proxy signatures that captures a more realistic set of attacks than previous models of Boldyreva et al. and of Malkin et al.. Our model is motivated by concrete attacks on existing schemes in scenarios in which proxy signatures are likely to be used. We provide a generic construction for proxy signatures secure in our enhanced model using sequential aggregate signatures; our construction provides a benchmark by which future specific constructions may be judged. Finally, we consider the extension of our model and constructions to the identity-based setting.