1use crate::{Fq, Fr};
 2use ark_ec::{
 3    models::CurveConfig,
 4    twisted_edwards::{Affine, MontCurveConfig, Projective, TECurveConfig},
 5};
 6use ark_ff::MontFp;
 7
 8#[cfg(test)]
 9mod tests;
10
11pub type EdwardsAffine = Affine<EdwardsParameters>;
12pub type EdwardsProjective = Projective<EdwardsParameters>;
13
14#[derive(Clone, Default, PartialEq, Eq)]
15pub struct EdwardsParameters;
16
17impl CurveConfig for EdwardsParameters {
18    type BaseField = Fq;
19    type ScalarField = Fr;
20
21    /// COFACTOR = 8
22    const COFACTOR: &'static [u64] = &[8];
23
24    /// COFACTOR_INV (mod r) =
25    /// 2713877091499598330239944961141122840321418634767465352250731601857045344121
26    const COFACTOR_INV: Fr =
27        MontFp!("2713877091499598330239944961141122840321418634767465352250731601857045344121");
28}
29
30impl TECurveConfig for EdwardsParameters {
31    /// COEFF_A = -1
32    const COEFF_A: Fq = MontFp!("-1");
33
34    /// COEFF_D = -121665 / 121666
35    const COEFF_D: Fq =
36        MontFp!("37095705934669439343138083508754565189542113879843219016388785533085940283555");
37
38    /// Standard generators from <https://neuromancer.sk/std/other/Ed25519>.
39    const GENERATOR: EdwardsAffine = EdwardsAffine::new_unchecked(GENERATOR_X, GENERATOR_Y);
40
41    type MontCurveConfig = EdwardsParameters;
42
43    /// Multiplication by `a` is just negation.
44    #[inline(always)]
45    fn mul_by_a(elem: Self::BaseField) -> Self::BaseField {
46        -elem
47    }
48}
49
50// We want to emphasize that this Montgomery curve is not Curve25519.
51impl MontCurveConfig for EdwardsParameters {
52    /// COEFF_A = 486662
53    const COEFF_A: Fq = MontFp!("486662");
54
55    /// COEFF_B = 57896044618658097711785492504343953926634992332820282019728792003956564333285
56    /// This is not one, because ed25519 != curve25519
57    const COEFF_B: Fq =
58        MontFp!("57896044618658097711785492504343953926634992332820282019728792003956564333285");
59
60    type TECurveConfig = EdwardsParameters;
61}
62
63/// GENERATOR_X =
64/// 15112221349535400772501151409588531511454012693041857206046113283949847762202
65const GENERATOR_X: Fq =
66    MontFp!("15112221349535400772501151409588531511454012693041857206046113283949847762202");
67
68/// GENERATOR_Y =
69/// (4/5)
70/// 46316835694926478169428394003475163141307993866256225615783033603165251855960
71const GENERATOR_Y: Fq =
72    MontFp!("46316835694926478169428394003475163141307993866256225615783033603165251855960");