Cryptanalysis and Improvement on An ID-Based Key Issuing Protocol

In this paper we analyze an ID-based key issuing protocol due to Gangishetti et al., designed for eliminating the need of secure channel between PKG and users and avoiding the key escrow problem. Their protocol consists of five sub-protocols, namely System Setup, System Public Key Setup, Key Issuing, Key Securing and Key Retrieving. We show that both the Key Issuing and the Key Securing subprotocols suffer from impersonation attacks. Further, we present an improved key issuing protocol which is proved to be secure against adaptive chosen message attack in the random oracle model under the CDH assumption.