Identity-based Conditional Privacy-Preserving Authentication Scheme Resistant to Malicious Subliminal Setting of Ephemeral Secret

In this paper we propose a modification of the Identity Based Conditional Privacy-Preserving Authentication Scheme (CPPA), which is based on Schnorr Signature Scheme (SS). The applicability and the security of the scheme is mainly considered in Intelligent Transportation Systems. We discuss scenarios with subliminal malicious setting of a ephemeral secret. We present a new, stronger security model for the scheme in which we allow the adversary to choose random values used during signing process. We define the SS to be secure if the advantage of the adversary in this model is negligible. Finally we prove the security of the modified Identity Based CPPA in our stronger model.