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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,3 +1,6 @@ | ||
| //! Features expected to land into Arkworks at some point in the future | ||
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| /// Elligator 2 hash-to-curve. | ||
| pub mod elligator2; | ||
| /// Twisted Edwards to Short Weierstrass mapping. | ||
| pub mod te_sw_map; |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,106 @@ | ||
| use crate::*; | ||
| use ark_ec::{ | ||
| short_weierstrass::{Affine as WeierstrassAffine, SWCurveConfig}, | ||
| twisted_edwards::{Affine as EdwardsAffine, MontCurveConfig, TECurveConfig}, | ||
| CurveConfig, | ||
| }; | ||
| use ark_ff::{Field, One}; | ||
| use ark_std::borrow::Cow; | ||
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| // Constants used in mapping TE form to SW form and vice versa | ||
| pub trait MapConfig: TECurveConfig + SWCurveConfig + MontCurveConfig { | ||
| const MONT_A_OVER_THREE: <Self as CurveConfig>::BaseField; | ||
| const MONT_B_INV: <Self as CurveConfig>::BaseField; | ||
| } | ||
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| pub fn map_sw_to_te<C: MapConfig>(point: &WeierstrassAffine<C>) -> Option<EdwardsAffine<C>> { | ||
| // First map the point from SW to Montgomery | ||
| // (Bx - A/3, By) | ||
| let mx = <C as MontCurveConfig>::COEFF_B * point.x - C::MONT_A_OVER_THREE; | ||
| let my = <C as MontCurveConfig>::COEFF_B * point.y; | ||
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| // Then we map the TE point to Montgamory | ||
| // (x,y) -> (x/y,(x−1)/(x+1)) | ||
| let v_denom = my.inverse()?; | ||
| let x_p_1 = mx + <<C as CurveConfig>::BaseField as One>::one(); | ||
| let w_denom = x_p_1.inverse()?; | ||
| let v = mx * v_denom; | ||
| let w = (mx - <<C as CurveConfig>::BaseField as One>::one()) * w_denom; | ||
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| Some(EdwardsAffine::new_unchecked(v, w)) | ||
| } | ||
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| pub fn map_te_to_sw<C: MapConfig>(point: &EdwardsAffine<C>) -> Option<WeierstrassAffine<C>> { | ||
| // Map from TE to Montgomery: (1+y)/(1-y), (1+y)/(x(1-y)) | ||
| let v_denom = <<C as CurveConfig>::BaseField as One>::one() - point.y; | ||
| let w_denom = point.x - point.x * point.y; | ||
| let v_denom_inv = v_denom.inverse()?; | ||
| let w_denom_inv = w_denom.inverse()?; | ||
| let v_w_num = <<C as CurveConfig>::BaseField as One>::one() + point.y; | ||
| let v = v_w_num * v_denom_inv; | ||
| let w = v_w_num * w_denom_inv; | ||
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| // Map Montgamory to SW: ((x+A/3)/B,y/B) | ||
| let x = C::MONT_B_INV * (v + C::MONT_A_OVER_THREE); | ||
| let y = C::MONT_B_INV * w; | ||
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| Some(WeierstrassAffine::new_unchecked(x, y)) | ||
| } | ||
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| pub trait SWMapping<C: SWCurveConfig> { | ||
| fn from_sw(sw: WeierstrassAffine<C>) -> Self; | ||
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| fn into_sw(self) -> WeierstrassAffine<C>; | ||
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| fn to_sw_slice(slice: &[Self]) -> Cow<[WeierstrassAffine<C>]> | ||
| where | ||
| Self: Sized; | ||
| } | ||
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| impl<C: SWCurveConfig> SWMapping<C> for WeierstrassAffine<C> { | ||
| #[inline(always)] | ||
| fn from_sw(sw: WeierstrassAffine<C>) -> Self { | ||
| sw | ||
| } | ||
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| #[inline(always)] | ||
| fn into_sw(self) -> WeierstrassAffine<C> { | ||
| self | ||
| } | ||
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| #[inline(always)] | ||
| fn to_sw_slice(slice: &[Self]) -> Cow<[WeierstrassAffine<C>]> { | ||
| Cow::Borrowed(slice) | ||
| } | ||
| } | ||
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| impl<C: MapConfig> SWMapping<C> for EdwardsAffine<C> { | ||
| #[inline(always)] | ||
| fn from_sw(sw: WeierstrassAffine<C>) -> Self { | ||
| const ERR_MSG: &str = | ||
| "SW to TE is expected to be implemented only for curves supporting the mapping"; | ||
| map_sw_to_te(&sw).expect(ERR_MSG) | ||
| } | ||
|
|
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| #[inline(always)] | ||
| fn into_sw(self) -> WeierstrassAffine<C> { | ||
| const ERR_MSG: &str = | ||
| "TE to SW is expected to be implemented only for curves supporting the mapping"; | ||
| map_te_to_sw(&self).expect(ERR_MSG) | ||
| } | ||
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| #[inline(always)] | ||
| fn to_sw_slice(slice: &[Self]) -> Cow<[WeierstrassAffine<C>]> { | ||
| let pks; | ||
| #[cfg(feature = "parallel")] | ||
| { | ||
| use rayon::prelude::*; | ||
| pks = slice.par_iter().map(|p| p.into_sw()).collect(); | ||
| } | ||
| #[cfg(not(feature = "parallel"))] | ||
| { | ||
| pks = slice.iter().map(|p| p.into_sw()).collect(); | ||
| } | ||
| Cow::Owned(pks) | ||
| } | ||
| } |
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