Identity-Based Signature Scheme Secure in Ephemeral Setup and Leakage Scenarios.

We propose the identity-based signature (IBS) scheme resilient to ephemerals leakage and setup. The scheme is applicable to scenarios, where signers can not trust thoroughly the signing devices, and doubts about the fairness of randomness the hardware and the operating system generate are justified. Our construction is based on the lightweight IBS by Galindo and Garcia. We present a formal security model for IBS in which all values coming from randomness source in signing procedure are leaked or set by adversary. We argue that the original scheme is vulnerable to universal forgery in our security model. We give details on our modified construction and provide a formal security proof in Random Oracle Model, claiming that even such a strong adversary cannot forge a signature in our scheme.