Abstract.In this paper, the computational complexity to compute a scalar multiplication on classes of elliptic curve over a prime field that have efficiently-computable endomorphisms is analyzed mathematically. This scalar multiplication is called integer sub-decomposition (ISD) method, which is based on the GLV method of Gallant, Lambert and Vanstone that was initially proposed in the year 2001. In this work, the mathematical proof of the computational cost of ISD implementation is presented. The computational cost of ISD algorithm has been proven based on the operations counting. Two types of the operations are used, namely, elliptic curve operations represented by elliptic curve point addition A and elliptic curve point doubling D and finite field operations represented by field inversion I, field multiplication M and field squaring S that design the computation of the running time of ISD scalar multiplication.
Key words and phrases:Elliptic curves, scalar multiplication, efficiently-computable endomorphisms, integer sub-decomposition, computational complexity.
IntroductionThe attractive features of elliptic curves history awarded it studying by mathematicians over a hundred of years to solve a variety of problems. The entry of these curves into cryptography independently by Neal Koblitz [1] and Victor Miller [2] in 1985 who suggested elliptic curve public key cryptosystems. The elliptic curves performance has active importance in the security level as a traditional asymmetric cryptosystem, such as RSA [3], [4]. The fundamental step of elliptic curve cryptosystems is to compute elliptic curve scalar multiplication kP for a point P which has a large prime order n. To accomplish this end, various methods have been innovated, adopting on elliptic curves E over finite fields. A group of methods cleverly employs a distinguished endomorphism ψ ∈ End(E) to split a large computation into a sequence of cheaper ones, so that the overall computational cost will be lowered [3].Recently, Gallant, Lambert and Vanstone [5], [6], [7] used such a technique that, contrary to the previous ones, also applied to special curves defined over large prime fields. Their method uses an efficiently computable endomorphism ψ ∈ End(E) to rewrite kP as