I. Introduction
Elliptic curve cryptosystems (ECC), independently introduced by Miller [11] and Koblitz [9], have now found significant place in the academic literature and practical applications. Their popularity is mainly because of their shorter key-sizes, which offer the same level of security as other conventional cryptosystems such as RSA. The security of ECC relies on the difficulty of Elliptic Curve Discrete Logarithmic Problem (ECDLP) [10]. By definition, ECDLP is to find an integer for two points and on an elliptic curve such that Q=[n]P \eqno{\hbox{(1)}}
Here, denotes the scalar multiplication with .