Efficient and secure pairing-free certificateless directed signature scheme

Abstract

In an ordinary signature scheme any one can verify the validity of a signature produced by the signer. But public verifiability of signatures is not desirable in some applications where the signed message is sensitive to the signature receiver, for example signatures on medical records, tax information. To meet this requirement, the concept of directed signature was introduced. A directed signature scheme is a kind of signature scheme in which the verification ability is controlled by the signer. Many directed signature schemes have been proposed in different cryptographic settings and most of the schemes are using bilinear pairings over elliptic curves. But the computation of a bilinear pairing is very expensive. Hence the schemes which use pairings are less efficient and are not much applicable in practice. In order to improve the computational and communicational efficiency, in this paper, we propose a pairing- free certificateless directed signature scheme. The proposed scheme is proven secure in the random oracle model under the assumption that the elliptic curve discrete logarithm problem is hard. We compare our scheme with well known existing schemes and efficiency analysis shows that the proposed scheme is more efficient.