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D.11.3.33 generateG
Procedure from library crypto.lib (see crypto_lib).
- Usage:
- generateG(a,b,m);
- Return:
- m-th division polynomial
- Note:
- generate the recursively defined polynomials in Z[x,y],so called
division polynomials, p_m=generateG(a,b,m) such that on the elliptic curve
defined by y^2=x^3+a*x+b over Z/N and a point P=(x:y:1) the point m*P is
(x-(p_(m-1)*p_(m+1))/p_m^2 :(p_(m+2)*p_(m-1)^2-p_(m-2)*p_(m+1)^2)/4y*p_m^3 :1)
m*P=0 iff p_m(P)=0
Example:
| LIB "crypto.lib";
ring R = 0,(x,y),dp;
generateG(7,15,4);
==> 4xy6+140xy4+1200xy3-980xy2-1680xy-8572x
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