Revocable Certificateless Public Key Encryption With Outsourced Semi-Trusted Cloud Revocation Agent

Abstract

Certificateless public key cryptography (CL-PKC) not only eliminates the need for certificates in traditional certificate-based PKC but also solves the inherent key escrow problem in identity-based PKC. However, an unsolved but critical issue in CL-PKC is how to revoke a misbehaving user. Some revocable certificateless public key encryption (RCL-PKE) schemes have been proposed, but these schemes have two main drawbacks: 1) public key uniqueness is not guaranteed, thus allowing the existence of multiple copies of each initial secret key. 2) The existing outsourced RCL-PKE schemes place excessive trust in the cloud server, which may continue to update decryption keys stealthily for misbehaving users. In this paper, we address these issues by proposing a novel RCL-PKE with semi-trusted cloud revocation agents (s-CRAs). We describe the framework and the security model for the RCL-PKE with s-CRA and prove that the proposed scheme is semantically secure against adaptive chosen-ciphertext attacks under the bilinear Diffie-Hellman assumption in the random oracle model. Furthermore, we compare the proposed scheme with previous RCL-PKE schemes in terms of performance and robustness. The evaluation results show that the proposed scheme achieves public key uniqueness and reliable revocation flexibility at low computational and communication costs.

Keywords

• Certificateless encryption
• revocable
• random oracle
• cloud computing
• outsourcing