1use ark_ec::{
  2    models::CurveConfig,
  3    short_weierstrass::{self, SWCurveConfig},
  4    twisted_edwards::{Affine, MontCurveConfig, Projective, TECurveConfig},
  5};
  6use ark_ff::MontFp;
  7
  8use crate::{Fq, Fr};
  9
 10#[cfg(test)]
 11mod tests;
 12
 13pub type EdwardsAffine = Affine<JubjubConfig>;
 14pub type EdwardsProjective = Projective<JubjubConfig>;
 15pub type SWAffine = short_weierstrass::Affine<JubjubConfig>;
 16pub type SWProjective = short_weierstrass::Projective<JubjubConfig>;
 17
 18/// `JubJub` is a twisted Edwards curve. These curves have equations of the
 19/// form: ax² + y² = 1 - dx²y².
 20/// over some base finite field Fq.
 21///
 22/// JubJub's curve equation: -x² + y² = 1 - (10240/10241)x²y²
 23///
 24/// q = 52435875175126190479447740508185965837690552500527637822603658699938581184513.
 25///
 26/// a = -1.
 27/// d = -(10240/10241) mod q
 28///   = 19257038036680949359750312669786877991949435402254120286184196891950884077233.
 29///
 30/// Sage script to calculate these:
 31///
 32/// ```text
 33/// q = 52435875175126190479447740508185965837690552500527637822603658699938581184513
 34/// Fq = GF(q)
 35/// d = -(Fq(10240)/Fq(10241))
 36/// ```
 37/// These parameters and the sage script obtained from:
 38/// <https://github.com/zcash/zcash/issues/2230#issuecomment-317182190>
 39///
 40///
 41/// `jubjub` also has a short Weierstrass curve form, following the
 42/// form: y² = x³ + A * x + B
 43/// where
 44///
 45/// A = 52296097456646850916096512823759002727550416093741407922227928430486925478210
 46/// B = 48351165704696163914533707656614864561753505123260775585269522553028192119009
 47///
 48/// We can use the script available
 49/// [here](https://github.com/zhenfeizhang/bandersnatch/blob/main/bandersnatch/script/jubjub.sage)
 50/// to convert between the different representations.
 51#[derive(Clone, Default, PartialEq, Eq)]
 52pub struct JubjubConfig;
 53pub type EdwardsConfig = JubjubConfig;
 54pub type SWConfig = JubjubConfig;
 55
 56impl CurveConfig for JubjubConfig {
 57    type BaseField = Fq;
 58    type ScalarField = Fr;
 59
 60    /// COFACTOR = 8
 61    const COFACTOR: &'static [u64] = &[8];
 62
 63    /// COFACTOR^(-1) mod r =
 64    /// 819310549611346726241370945440405716213240158234039660170669895299022906775
 65    const COFACTOR_INV: Fr =
 66        MontFp!("819310549611346726241370945440405716213240158234039660170669895299022906775");
 67}
 68
 69impl TECurveConfig for JubjubConfig {
 70    /// COEFF_A = -1
 71    const COEFF_A: Fq = MontFp!("-1");
 72
 73    /// COEFF_D = -(10240/10241) mod q
 74    const COEFF_D: Fq =
 75        MontFp!("19257038036680949359750312669786877991949435402254120286184196891950884077233");
 76
 77    /// AFFINE_GENERATOR_COEFFS = (GENERATOR_X, GENERATOR_Y)
 78    const GENERATOR: EdwardsAffine = EdwardsAffine::new_unchecked(GENERATOR_X, GENERATOR_Y);
 79
 80    type MontCurveConfig = JubjubConfig;
 81
 82    /// Multiplication by `a` is simply negation here.
 83    #[inline(always)]
 84    fn mul_by_a(elem: Self::BaseField) -> Self::BaseField {
 85        -elem
 86    }
 87}
 88
 89impl MontCurveConfig for JubjubConfig {
 90    /// COEFF_A = 40962
 91    const COEFF_A: Fq = MontFp!("40962");
 92
 93    /// COEFF_B = -40964
 94    const COEFF_B: Fq = MontFp!("-40964");
 95
 96    type TECurveConfig = JubjubConfig;
 97}
 98
 99const GENERATOR_X: Fq =
100    MontFp!("8076246640662884909881801758704306714034609987455869804520522091855516602923");
101
102const GENERATOR_Y: Fq =
103    MontFp!("13262374693698910701929044844600465831413122818447359594527400194675274060458");
104
105impl SWCurveConfig for JubjubConfig {
106    /// COEFF_A = 52296097456646850916096512823759002727550416093741407922227928430486925478210
107    const COEFF_A: Self::BaseField =
108        MontFp!("52296097456646850916096512823759002727550416093741407922227928430486925478210");
109
110    /// COEFF_B = 48351165704696163914533707656614864561753505123260775585269522553028192119009
111    const COEFF_B: Self::BaseField =
112        MontFp!("48351165704696163914533707656614864561753505123260775585269522553028192119009");
113
114    /// generators
115    const GENERATOR: SWAffine = SWAffine::new_unchecked(SW_GENERATOR_X, SW_GENERATOR_Y);
116}
117
118/// x coordinate for SW curve generator
119const SW_GENERATOR_X: Fq =
120    MontFp!("33835869156188682335217394949746694649676633840125476177319971163079011318731");
121
122/// y coordinate for SW curve generator
123const SW_GENERATOR_Y: Fq =
124    MontFp!("43777270878440091394432848052353307184915192688165709016756678962558652055320");