A revocable certificateless signature scheme

Certificateless public key cryptography (CLPKC), with properties of no key escrow and no certificate, has received a lot of attention since its invention. However, membership revocation in certificateless cryptosystem still remains a non-trivial problem: the existing solutions are not practical for use due to either a costly mediator or enormous computation (secret channel). In this paper, we present a new approach to revocation in CLPKC with a concrete construction of a revocable certificateless signature (RCLS) scheme. In our scheme, a user\u27s private key is composed of three parts: an initial partial private key, a time key and a secret value. The transmission of updated-key requires only a public channel, which makes our RCLS scheme more efficient than other methods. We first provide formal definition and security model for a RCLS scheme. The new scheme is proved secure in the random oracle model, based on the Computational Diffie-Hellman problem