Jubjub is the [twisted Edwards curve](https://en.wikipedia.org/wiki/Twisted_Edwards_curve) `-x^2 + y^2 = 1 + d.x^2.y^2` of rational points over `GF(q)` with a subgroup of prime order `r` and cofactor `8`.
The choice of `GF(q)` is made to be the scalar field of the BLS12-381 elliptic curve group.
Jubjub is birationally equivalent to a [Montgomery curve](https://en.wikipedia.org/wiki/Montgomery_curve) `y^2 = x^3 + Ax^2 + x` over the same field with `A = 40962`. This value of `A` is the smallest integer such that `(A - 2) / 4` is a small integer, `A^2 - 4` is nonsquare in `GF(q)`, and the Montgomery curve and its quadratic twist have small cofactors `8` and `4`, respectively. This is identical to the relationship between Curve25519 and ed25519.
Please see [./doc/evidence/](./doc/evidence/) for supporting evidence that Jubjub meets the [SafeCurves](https://safecurves.cr.yp.to/index.html) criteria. The tool in [./doc/derive/](./doc/derive/) will derive the curve parameters via the above criteria to demonstrate rigidity.