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### Defining a subgroup of elliptic curves with specific characteristics

Hey,

is there a way, to define a subgroup of an elliptic curve with two or more characteristics? I would like to take an elliptic curve over a finite field of order p and $p^4$, define the r-torsion subgroup (where $r$ is a prime, too) and reduce those to the set of points, which also lays in the Frobenius-eigenspace.

For example:

p= 13
r=5
R=GF(p)
_.<x> = PolynomialRing(R)
R4.<x> = R.extension(x^4 - 2, 'x')
_.<y> = PolynomialRing(R)

b= x^-1

E = EllipticCurve(R, [1,0]) # y^2 = x^3+x
E4 = EllipticCurve(R4, [b,0])


Well, it is easy to find a point on $Q\in E4$, such that $r*Q = (0:1:0)$, use

Q=ZZ(E4.order()/r *Q


, but checking, if $\pi(Q) = pQ$ is hard. I only need one point of that group at all, but my $p$ is even larger, so brute-forcing would be an option, if I could start it 6-12 month ago :)

### Defining a subgroup of elliptic curves with specific characteristics

Hey,

is there a way, to define a subgroup of an elliptic curve with two or more characteristics? I would like to take an elliptic curve over a finite field of order p and $p^4$, define the r-torsion subgroup (where $r$ is a prime, too) and reduce those to the set of points, which also lays in the Frobenius-eigenspace.

For example:

p= 13
r=5
R=GF(p)
_.<x> = PolynomialRing(R)
R4.<x> = R.extension(x^4 - 2, 'x')
_.<y> = PolynomialRing(R)

b= x^-1

E = EllipticCurve(R, [1,0]) # y^2 = x^3+x
E4 = EllipticCurve(R4, [b,0])


Well, it is easy to find a point on $Q\in E4$, such that $r*Q = (0:1:0)$, use

Q=ZZ(E4.order()/r *Q