Jubjub is a twisted Edwards curve defined over the BLS12-381 scalar
field, Fr. It takes the form -x^2 + y^2 = 1 + dx^2y^2 with
d = -(10240/10241). It is birationally equivalent to a Montgomery
curve of the form y^2 = x^3 + Ax^2 + x with A = 40962. This
value A is the smallest integer choice such that: