Merge pull request #55 from zcash/fieldext-finale

Remove `FieldExt` and `Group` traits

CHANGELOG.md

@@ -10,10 +10,11 @@ and this project adheres to Rust's notion of
 - Migrated to `ff 0.13`, `group 0.13`.
 
 ### Removed
-- `pasta_curves::arithmetic::SqrtRatio` (use `ff::Field::{sqrt_ratio, sqrt_alt}`
+- `pasta_curves::arithmetic`:
-  instead).
+  - `FieldExt` (use `ff::PrimeField` or `ff::WithSmallOrderMulGroup` instead).
-- `pasta_curves::arithmetic::SqrtTables` (from public API, as it isn't suitable
+  - `Group`
-  for generic usage).
+  - `SqrtRatio` (use `ff::Field::{sqrt_ratio, sqrt_alt}` instead).
+  - `SqrtTables` (from public API, as it isn't suitable for generic usage).
 
 ## [0.4.1] - 2022-10-13
 ### Added

Cargo.toml

@@ -74,4 +74,4 @@ uninline-portable = []
 serde = ["hex", "serde_crate"]
 
 [patch.crates-io]
-ff = { git = "https://github.com/zkcrypto/ff.git", rev = "c070ffbaea8cb17e57f817a91ed0e364ff679b7c" }
+ff = { git = "https://github.com/zkcrypto/ff.git", rev = "054a4d2daf9a9540d4c436fa51f0222e997ad15c" }

src/arithmetic.rs

@@ -8,25 +8,4 @@ mod curves;
 mod fields;
 
 pub use curves::*;
-pub use fields::*;
+pub(crate) use fields::*;
-
-/// This represents an element of a group with basic operations that can be
-/// performed. This allows an FFT implementation (for example) to operate
-/// generically over either a field or elliptic curve group.
-pub trait Group: Copy + Clone + Send + Sync + 'static {
-    /// The group is assumed to be of prime order $p$. `Scalar` is the
-    /// associated scalar field of size $p$.
-    type Scalar: FieldExt;
-
-    /// Returns the additive identity of the group.
-    fn group_zero() -> Self;
-
-    /// Adds `rhs` to this group element.
-    fn group_add(&mut self, rhs: &Self);
-
-    /// Subtracts `rhs` from this group element.
-    fn group_sub(&mut self, rhs: &Self);
-
-    /// Scales this group element by a scalar.
-    fn group_scale(&mut self, by: &Self::Scalar);
-}

src/arithmetic/curves.rs

@@ -6,9 +6,6 @@ use group::prime::{PrimeCurve, PrimeCurveAffine};
 #[cfg(feature = "alloc")]
 use subtle::{Choice, ConditionallySelectable, ConstantTimeEq, CtOption};
 
-#[cfg(feature = "alloc")]
-use super::{FieldExt, Group};
-
 #[cfg(feature = "alloc")]
 use alloc::boxed::Box;
 #[cfg(feature = "alloc")]
@@ -28,12 +25,11 @@ pub trait CurveExt:
     + ConditionallySelectable
     + ConstantTimeEq
     + From<<Self as PrimeCurve>::Affine>
-    + Group<Scalar = <Self as group::Group>::Scalar>
 {
     /// The scalar field of this elliptic curve.
-    type ScalarExt: FieldExt;
+    type ScalarExt: ff::WithSmallOrderMulGroup<3>;
     /// The base field over which this elliptic curve is constructed.
-    type Base: FieldExt;
+    type Base: ff::WithSmallOrderMulGroup<3>;
     /// The affine version of the curve
     type AffineExt: CurveAffine<CurveExt = Self, ScalarExt = <Self as CurveExt>::ScalarExt>
         + Mul<Self::ScalarExt, Output = Self>
@@ -103,9 +99,9 @@ pub trait CurveAffine:
     + From<<Self as PrimeCurveAffine>::Curve>
 {
     /// The scalar field of this elliptic curve.
-    type ScalarExt: FieldExt;
+    type ScalarExt: ff::WithSmallOrderMulGroup<3> + Ord;
     /// The base field over which this elliptic curve is constructed.
-    type Base: FieldExt;
+    type Base: ff::WithSmallOrderMulGroup<3> + Ord;
     /// The projective form of the curve
     type CurveExt: CurveExt<AffineExt = Self, ScalarExt = <Self as CurveAffine>::ScalarExt>;
 

src/arithmetic/fields.rs

@@ -5,8 +5,6 @@ use core::mem::size_of;
 
 use static_assertions::const_assert;
 
-use super::Group;
-
 #[cfg(feature = "sqrt-table")]
 use alloc::{boxed::Box, vec::Vec};
 #[cfg(feature = "sqrt-table")]
@@ -30,48 +28,18 @@ pub(crate) trait SqrtTableHelpers: ff::PrimeField {
     fn get_lower_32(&self) -> u32;
 }
 
-/// This trait is a common interface for dealing with elements of a finite
-/// field.
-pub trait FieldExt: ff::PrimeField + From<bool> + Ord + Group<Scalar = Self> {
-    /// Modulus of the field written as a string for display purposes
-    const MODULUS: &'static str;
-
-    /// Inverse of `PrimeField::ROOT_OF_UNITY`
-    const ROOT_OF_UNITY_INV: Self;
-
-    /// Generator of the $t-order$ multiplicative subgroup
-    const DELTA: Self;
-
-    /// Inverse of $2$ in the field.
-    const TWO_INV: Self;
-
-    /// Element of multiplicative order $3$.
-    const ZETA: Self;
-
-    /// Obtains a field element congruent to the integer `v`.
-    fn from_u128(v: u128) -> Self;
-
-    /// Obtains a field element that is congruent to the provided little endian
-    /// byte representation of an integer.
-    fn from_bytes_wide(bytes: &[u8; 64]) -> Self;
-
-    /// Gets the lower 128 bits of this field element when expressed
-    /// canonically.
-    fn get_lower_128(&self) -> u128;
-}
-
 /// Parameters for a perfect hash function used in square root computation.
 #[cfg(feature = "sqrt-table")]
 #[cfg_attr(docsrs, doc(cfg(feature = "sqrt-table")))]
 #[derive(Debug)]
-struct SqrtHasher<F: FieldExt> {
+struct SqrtHasher<F: SqrtTableHelpers> {
     hash_xor: u32,
     hash_mod: usize,
     marker: PhantomData<F>,
 }
 
 #[cfg(feature = "sqrt-table")]
-impl<F: FieldExt + SqrtTableHelpers> SqrtHasher<F> {
+impl<F: SqrtTableHelpers> SqrtHasher<F> {
     /// Returns a perfect hash of x for use with SqrtTables::inv.
     fn hash(&self, x: &F) -> usize {
         // This is just the simplest constant-time perfect hash construction that could
@@ -86,7 +54,7 @@ impl<F: FieldExt + SqrtTableHelpers> SqrtHasher<F> {
 #[cfg(feature = "sqrt-table")]
 #[cfg_attr(docsrs, doc(cfg(feature = "sqrt-table")))]
 #[derive(Debug)]
-pub(crate) struct SqrtTables<F: FieldExt> {
+pub(crate) struct SqrtTables<F: SqrtTableHelpers> {
     hasher: SqrtHasher<F>,
     inv: Vec<u8>,
     g0: Box<[F; 256]>,
@@ -96,7 +64,7 @@ pub(crate) struct SqrtTables<F: FieldExt> {
 }
 
 #[cfg(feature = "sqrt-table")]
-impl<F: FieldExt + SqrtTableHelpers> SqrtTables<F> {
+impl<F: SqrtTableHelpers> SqrtTables<F> {
     /// Build tables given parameters for the perfect hash.
     pub fn new(hash_xor: u32, hash_mod: usize) -> Self {
         use alloc::vec;

src/curves.rs

@@ -18,11 +18,13 @@ use group::{
 use rand::RngCore;
 use subtle::{Choice, ConditionallySelectable, ConstantTimeEq, CtOption};
 
+#[cfg(feature = "alloc")]
+use ff::WithSmallOrderMulGroup;
+
 use super::{Fp, Fq};
-use crate::arithmetic::Group;
 
 #[cfg(feature = "alloc")]
-use crate::arithmetic::{Coordinates, CurveAffine, CurveExt, FieldExt};
+use crate::arithmetic::{Coordinates, CurveAffine, CurveExt};
 
 macro_rules! new_curve_impl {
     (($($privacy:tt)*), $name:ident, $name_affine:ident, $iso:ident, $base:ident, $scalar:ident,
@@ -783,23 +785,6 @@ macro_rules! new_curve_impl {
         impl_binops_multiplicative!($name, $scalar);
         impl_binops_multiplicative_mixed!($name_affine, $scalar, $name);
 
-        impl Group for $name {
-            type Scalar = $scalar;
-
-            fn group_zero() -> Self {
-                Self::identity()
-            }
-            fn group_add(&mut self, rhs: &Self) {
-                *self += *rhs;
-            }
-            fn group_sub(&mut self, rhs: &Self) {
-                *self -= *rhs;
-            }
-            fn group_scale(&mut self, by: &Self::Scalar) {
-                *self *= *by;
-            }
-        }
-
         #[cfg(feature = "gpu")]
         impl ec_gpu::GpuName for $name_affine {
             fn name() -> alloc::string::String {

src/fields/fp.rs

@@ -1,7 +1,7 @@
 use core::fmt;
 use core::ops::{Add, Mul, Neg, Sub};
 
-use ff::{Field, PrimeField};
+use ff::{Field, FromUniformBytes, PrimeField, WithSmallOrderMulGroup};
 use rand::RngCore;
 use subtle::{Choice, ConditionallySelectable, ConstantTimeEq, CtOption};
 
@@ -11,7 +11,7 @@ use lazy_static::lazy_static;
 #[cfg(feature = "bits")]
 use ff::{FieldBits, PrimeFieldBits};
 
-use crate::arithmetic::{adc, mac, sbb, FieldExt, Group, SqrtTableHelpers};
+use crate::arithmetic::{adc, mac, sbb, SqrtTableHelpers};
 
 #[cfg(feature = "sqrt-table")]
 use crate::arithmetic::SqrtTables;
@@ -475,23 +475,6 @@ impl<'a> From<&'a Fp> for [u8; 32] {
     }
 }
 
-impl Group for Fp {
-    type Scalar = Fp;
-
-    fn group_zero() -> Self {
-        Self::zero()
-    }
-    fn group_add(&mut self, rhs: &Self) {
-        *self += *rhs;
-    }
-    fn group_sub(&mut self, rhs: &Self) {
-        *self -= *rhs;
-    }
-    fn group_scale(&mut self, by: &Self::Scalar) {
-        *self *= *by;
-    }
-}
-
 impl ff::Field for Fp {
     const ZERO: Self = Self::zero();
     const ONE: Self = Self::one();
@@ -580,11 +563,30 @@ impl ff::Field for Fp {
 impl ff::PrimeField for Fp {
     type Repr = [u8; 32];
 
+    const MODULUS: &'static str =
+        "0x40000000000000000000000000000000224698fc094cf91b992d30ed00000001";
+    const TWO_INV: Self = Fp::from_raw([
+        0xcc96987680000001,
+        0x11234c7e04a67c8d,
+        0x0000000000000000,
+        0x2000000000000000,
+    ]);
     const NUM_BITS: u32 = 255;
     const CAPACITY: u32 = 254;
     const MULTIPLICATIVE_GENERATOR: Self = GENERATOR;
     const S: u32 = S;
     const ROOT_OF_UNITY: Self = ROOT_OF_UNITY;
+    const ROOT_OF_UNITY_INV: Self = Fp::from_raw([
+        0xf0b87c7db2ce91f6,
+        0x84a0a1d8859f066f,
+        0xb4ed8e647196dad1,
+        0x2cd5282c53116b5c,
+    ]);
+    const DELTA: Self = DELTA;
+
+    fn from_u128(v: u128) -> Self {
+        Fp::from_raw([v as u64, (v >> 64) as u64, 0, 0])
+    }
 
     fn from_repr(repr: Self::Repr) -> CtOption<Self> {
         let mut tmp = Fp([0, 0, 0, 0]);
@@ -726,36 +728,19 @@ impl SqrtTableHelpers for Fp {
     }
 }
 
-impl FieldExt for Fp {
+impl WithSmallOrderMulGroup<3> for Fp {
-    const MODULUS: &'static str =
-        "0x40000000000000000000000000000000224698fc094cf91b992d30ed00000001";
-    const ROOT_OF_UNITY_INV: Self = Fp::from_raw([
-        0xf0b87c7db2ce91f6,
-        0x84a0a1d8859f066f,
-        0xb4ed8e647196dad1,
-        0x2cd5282c53116b5c,
-    ]);
-    const DELTA: Self = DELTA;
-    const TWO_INV: Self = Fp::from_raw([
-        0xcc96987680000001,
-        0x11234c7e04a67c8d,
-        0x0000000000000000,
-        0x2000000000000000,
-    ]);
     const ZETA: Self = Fp::from_raw([
         0x1dad5ebdfdfe4ab9,
         0x1d1f8bd237ad3149,
         0x2caad5dc57aab1b0,
         0x12ccca834acdba71,
     ]);
+}
 
-    fn from_u128(v: u128) -> Self {
+impl FromUniformBytes<64> for Fp {
-        Fp::from_raw([v as u64, (v >> 64) as u64, 0, 0])
-    }
-
     /// Converts a 512-bit little endian integer into
     /// a `Fp` by reducing by the modulus.
-    fn from_bytes_wide(bytes: &[u8; 64]) -> Fp {
+    fn from_uniform_bytes(bytes: &[u8; 64]) -> Fp {
         Fp::from_u512([
             u64::from_le_bytes(bytes[0..8].try_into().unwrap()),
             u64::from_le_bytes(bytes[8..16].try_into().unwrap()),
@@ -767,12 +752,6 @@ impl FieldExt for Fp {
             u64::from_le_bytes(bytes[56..64].try_into().unwrap()),
         ])
     }
-
-    fn get_lower_128(&self) -> u128 {
-        let tmp = Fp::montgomery_reduce(self.0[0], self.0[1], self.0[2], self.0[3], 0, 0, 0, 0);
-
-        u128::from(tmp.0[0]) | (u128::from(tmp.0[1]) << 64)
-    }
 }
 
 #[cfg(feature = "gpu")]

src/fields/fq.rs

@@ -1,7 +1,7 @@
 use core::fmt;
 use core::ops::{Add, Mul, Neg, Sub};
 
-use ff::{Field, PrimeField};
+use ff::{Field, FromUniformBytes, PrimeField, WithSmallOrderMulGroup};
 use rand::RngCore;
 use subtle::{Choice, ConditionallySelectable, ConstantTimeEq, CtOption};
 
@@ -11,7 +11,7 @@ use lazy_static::lazy_static;
 #[cfg(feature = "bits")]
 use ff::{FieldBits, PrimeFieldBits};
 
-use crate::arithmetic::{adc, mac, sbb, FieldExt, Group, SqrtTableHelpers};
+use crate::arithmetic::{adc, mac, sbb, SqrtTableHelpers};
 
 #[cfg(feature = "sqrt-table")]
 use crate::arithmetic::SqrtTables;
@@ -475,23 +475,6 @@ impl<'a> From<&'a Fq> for [u8; 32] {
     }
 }
 
-impl Group for Fq {
-    type Scalar = Fq;
-
-    fn group_zero() -> Self {
-        Self::zero()
-    }
-    fn group_add(&mut self, rhs: &Self) {
-        *self += *rhs;
-    }
-    fn group_sub(&mut self, rhs: &Self) {
-        *self -= *rhs;
-    }
-    fn group_scale(&mut self, by: &Self::Scalar) {
-        *self *= *by;
-    }
-}
-
 impl ff::Field for Fq {
     const ZERO: Self = Self::zero();
     const ONE: Self = Self::one();
@@ -580,11 +563,30 @@ impl ff::Field for Fq {
 impl ff::PrimeField for Fq {
     type Repr = [u8; 32];
 
+    const MODULUS: &'static str =
+        "0x40000000000000000000000000000000224698fc0994a8dd8c46eb2100000001";
     const NUM_BITS: u32 = 255;
     const CAPACITY: u32 = 254;
+    const TWO_INV: Self = Fq::from_raw([
+        0xc623759080000001,
+        0x11234c7e04ca546e,
+        0x0000000000000000,
+        0x2000000000000000,
+    ]);
     const MULTIPLICATIVE_GENERATOR: Self = GENERATOR;
     const S: u32 = S;
     const ROOT_OF_UNITY: Self = ROOT_OF_UNITY;
+    const ROOT_OF_UNITY_INV: Self = Fq::from_raw([
+        0x57eecda0a84b6836,
+        0x4ad38b9084b8a80c,
+        0xf4c8f353124086c1,
+        0x2235e1a7415bf936,
+    ]);
+    const DELTA: Self = DELTA;
+
+    fn from_u128(v: u128) -> Self {
+        Fq::from_raw([v as u64, (v >> 64) as u64, 0, 0])
+    }
 
     fn from_repr(repr: Self::Repr) -> CtOption<Self> {
         let mut tmp = Fq([0, 0, 0, 0]);
@@ -725,36 +727,19 @@ impl SqrtTableHelpers for Fq {
     }
 }
 
-impl FieldExt for Fq {
+impl WithSmallOrderMulGroup<3> for Fq {
-    const MODULUS: &'static str =
-        "0x40000000000000000000000000000000224698fc0994a8dd8c46eb2100000001";
-    const ROOT_OF_UNITY_INV: Self = Fq::from_raw([
-        0x57eecda0a84b6836,
-        0x4ad38b9084b8a80c,
-        0xf4c8f353124086c1,
-        0x2235e1a7415bf936,
-    ]);
-    const DELTA: Self = DELTA;
-    const TWO_INV: Self = Fq::from_raw([
-        0xc623759080000001,
-        0x11234c7e04ca546e,
-        0x0000000000000000,
-        0x2000000000000000,
-    ]);
     const ZETA: Self = Fq::from_raw([
         0x2aa9d2e050aa0e4f,
         0x0fed467d47c033af,
         0x511db4d81cf70f5a,
         0x06819a58283e528e,
     ]);
+}
 
-    fn from_u128(v: u128) -> Self {
+impl FromUniformBytes<64> for Fq {
-        Fq::from_raw([v as u64, (v >> 64) as u64, 0, 0])
-    }
-
     /// Converts a 512-bit little endian integer into
     /// a `Fq` by reducing by the modulus.
-    fn from_bytes_wide(bytes: &[u8; 64]) -> Fq {
+    fn from_uniform_bytes(bytes: &[u8; 64]) -> Fq {
         Fq::from_u512([
             u64::from_le_bytes(bytes[0..8].try_into().unwrap()),
             u64::from_le_bytes(bytes[8..16].try_into().unwrap()),
@@ -766,12 +751,6 @@ impl FieldExt for Fq {
             u64::from_le_bytes(bytes[56..64].try_into().unwrap()),
         ])
     }
-
-    fn get_lower_128(&self) -> u128 {
-        let tmp = Fq::montgomery_reduce(self.0[0], self.0[1], self.0[2], self.0[3], 0, 0, 0, 0);
-
-        u128::from(tmp.0[0]) | (u128::from(tmp.0[1]) << 64)
-    }
 }
 
 #[cfg(feature = "gpu")]

src/hashtocurve.rs

@@ -1,13 +1,14 @@
 //! This module implements "simplified SWU" hashing to short Weierstrass curves
 //! with a = 0.
 
+use ff::{Field, FromUniformBytes, PrimeField};
 use static_assertions::const_assert;
 use subtle::ConstantTimeEq;
 
-use crate::arithmetic::{CurveExt, FieldExt};
+use crate::arithmetic::CurveExt;
 
 /// Hashes over a message and writes the output to all of `buf`.
-pub fn hash_to_field<F: FieldExt>(
+pub fn hash_to_field<F: FromUniformBytes<64>>(
     curve_id: &str,
     domain_prefix: &str,
     message: &[u8],
@@ -72,12 +73,12 @@ pub fn hash_to_field<F: FieldExt>(
         let mut little = [0u8; CHUNKLEN];
         little.copy_from_slice(big.as_array());
         little.reverse();
-        *buf = F::from_bytes_wide(&little);
+        *buf = F::from_uniform_bytes(&little);
     }
 }
 
 /// Implements a degree 3 isogeny map.
-pub fn iso_map<F: FieldExt, C: CurveExt<Base = F>, I: CurveExt<Base = F>>(
+pub fn iso_map<F: Field, C: CurveExt<Base = F>, I: CurveExt<Base = F>>(
     p: &I,
     iso: &[C::Base; 13],
 ) -> C {
@@ -105,7 +106,7 @@ pub fn iso_map<F: FieldExt, C: CurveExt<Base = F>, I: CurveExt<Base = F>>(
 }
 
 #[allow(clippy::many_single_char_names)]
-pub fn map_to_curve_simple_swu<F: FieldExt, C: CurveExt<Base = F>, I: CurveExt<Base = F>>(
+pub fn map_to_curve_simple_swu<F: PrimeField, C: CurveExt<Base = F>, I: CurveExt<Base = F>>(
     u: &F,
     theta: F,
     z: F,

src/lib.rs

@@ -39,8 +39,8 @@ pub extern crate group;
 #[cfg(feature = "alloc")]
 #[test]
 fn test_endo_consistency() {
-    use crate::arithmetic::{CurveExt, FieldExt};
+    use crate::arithmetic::CurveExt;
-    use group::Group;
+    use group::{ff::WithSmallOrderMulGroup, Group};
 
     let a = pallas::Point::generator();
     assert_eq!(a * pallas::Scalar::ZETA, a.endo());