Abstract

Since public key cryptography is usually build using computationally expensive operation, it has been out of reach for resource constrained and low power devices. Today there are a large number of low power devices in use and they perform complex tasks. There is need for light weight cryptography having high security and low communication overhead. Online/Offline schemes are well suited for this purpose since they allow the use of public key cryptosystems in these low power devices. Many cryptosystems that are efficient in terms of number of computational steps may be inefficient if we consider the size of keys that must be used to achieve a acceptable level of security. Especially cryptosystems that have a loose security proof may work with large keys, this increases the communication overhead. In this paper, we show a view of the how Certificateless schemes are constructed. Then, we present a Certificateless Online/Offline Signature (CLOOS) Scheme and give a tight security reduction to the Gap Diffie-Hellman problem in the random oracle model. Even though other schemes exist that are are constructed using less number computational steps, if we take into account the size of keys our scheme will be more efficient. Thus, our scheme is light weight and has a low communication overhead.