Exponentiation By Squaring - 2k-ary Method

2k-ary Method

This algorithm calculates the value of xn after expanding the exponent in base 2k. It was first proposed by Brauer in 1939. In the algorithm below we make use of the following function f(0) = (k,0) and f(m) = (s,u) where m = u·2s with u odd.

Algorithm:

Input
An element x of G, a parameter k > 0, a non-negative integer n = (nl−1, nl−2, ..., n0)2k and the precomputed values x3, x5, ..., .
Output
The element xn in G
1. y := 1 and i := l-1 2. While i>=0 do 3. (s,u) := f(ni) 4. for j:=1 to k-s do 5. y := y2 6. y := y*xu 7. for j:=1 to s do 8. y := y2 9. i := i-1 10. return y

For optimal efficiency, k should be the smallest integer satisfying

Read more about this topic:  Exponentiation By Squaring

Famous quotes containing the word method:

    “There is assuredly no more effectual method of clearing up one’s own mind on any subject than by talking it over, so to speak, with men of real power and grasp, who have considered it from a totally different point of view.”
    —Thomas Henry Huxley (1825–95)