Generic Certificateless Encryption in the Standard Model

Despite the large number of certificateless encryption schemes recently proposed, many of them have been found to be insecure under a practical attack called malicious-but-passive KGC attack, since they all follow the same key generation procedure as that of the one proposed by Al-Riyami and Paterson in ASIACRYPT 2003. The only scheme that remains secure against this attack is due to Libert and Quisquater (PKC 2006). However, the security can only be shown in the random oracle model. In this paper, we first show that a scheme which has a different key generation procedure from that of Al-Riyami and Paterson also suffers from the malicious-but-passive KGC attack. Our attacking techniques are different and may cause greater extent of damage than the previous ones. We also propose a generic construction of certificateless encryption which can be proven secure against this attack in the standard model. This generic scheme not only is the first one proven secure in the standard model, but is also very efficient to instantiate. We also describe how to use short signature and hybrid encryption to construct highly efficient instantiations of this generic scheme.