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D.12.3.31 generateG
Procedure from library crypto.lib (see crypto_lib).
- Usage:
- generateG(a,b,m);
- Return:
- m-th division polynomial
- Note:
- generate the so-called division polynomials, i.e., the recursively defined
polynomials p_m=generateG(a,b,m) in Z[x, y] such that, for a point (x:y:1) on the
elliptic curve defined by y^2=x^3+a*x+b over Z/N the point
m*P=(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)
and m*P=0 if and only if 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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