A New Certificateless Signature Scheme Provably Secure in the Standard Model

Certificateless cryptography eliminates the need of certificates from public-key cryptography and solves the key escrow problem in identity-based cryptography. Since Al-Riyami and Paterson introduced the concept of certificateless cryptography, there have been several proposals for certificateless encryption schemes and signature schemes provably secure in the random oracle model. In the random oracle paradigm, the schemes make use of cryptographic hash functions that are modeled as random oracles in the security proof. However, it has been shown that when random oracles are instantiated with concrete hash functions, the schemes may not be secure. Afterward, several certificateless signature (CLS) schemes provably secure without random oracles have been proposed. However, it turned out that all the schemes are insecure against type I or II adversaries. In this paper, we propose a new CLS scheme secure in the standard model under the computational Diffie-Hellman assumption. We then investigate the practical feasibility of our scheme.