A supersingular elliptic curve is an elliptic curve over a field of positive characteristic whose group of geometric
-torsion points is trivial. Equivalently, its endomorphism
ring over an algebraic closure, tensored with the rational numbers, is a quaternion
algebra rather than an imaginary quadratic field. Supersingularity is preserved under
extension of the base field and under isogeny.
For an elliptic curve over the finite field ,
supersingularity can also be characterized by strong divisibility restrictions on
the trace of its Frobenius endomorphism.