Abstract

Public key cryptography usually is computationally more expensive than symmetric key systems. Due to this low power or resource constrained devices cannot make use of public key cryptosystems easily. There is a need for high security in these devices since many of these devices perform complex tasks which includes interaction with third party cloud infrastructures. These cloud infrastructures are not trusted entities. Hence there is need for light weight public key cryptography which are secure against these cloud administrators. The trusted entity in certificateless schemes cannot compromise the security of the users. Online/offline have two parts, first the computationally heavy part(offline) of the cryptosystem and then the main “online” algorithm for use on resource constrained devices. The heavy computations are done in the offline phase on a more powerful device. Hence, Certificate- less online/offline schemes are perfect for low power devices interacting with clouds. In this paper, we present a certificateless online/offline signature scheme. This scheme is the most efficient certifi- cateless signature scheme in existence and also has the added advantage of being online/offline. The scheme is proven secure in the random oracle model.