Move the contents of the evrf/ folder to the crypto/ folder

It was justified when it had several libraries, which it no longer does thanks
to the upstreaming with monero-oxide.

crypto/embedwards25519/src/lib.rs

@@ -0,0 +1,151 @@
+#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![doc = include_str!("../README.md")]
+#![cfg_attr(not(feature = "std"), no_std)]
+
+#[allow(unused_imports)]
+use std_shims::prelude::*;
+#[cfg(any(feature = "alloc", feature = "std"))]
+use std_shims::io::{self, Read};
+
+use prime_field::{subtle::Choice, zeroize::Zeroize};
+use ciphersuite::group::{
+  ff::{Field, PrimeField, FromUniformBytes},
+  Group,
+};
+
+use curve25519_dalek::Scalar as DalekScalar;
+pub use dalek_ff_group::Scalar as FieldElement;
+
+use short_weierstrass::{ShortWeierstrass, Affine, Projective};
+
+prime_field::odd_prime_field!(
+  Scalar,
+  "0fffffffffffffffffffffffffffffffe53f4debb78ff96877063f0306eef96b",
+  "0a",
+  false
+);
+
+#[derive(Clone, Copy, PartialEq, Eq, Debug, Zeroize)]
+pub struct Embedwards25519;
+
+#[allow(deprecated)] // No other way to construct arbitrary `FieldElement` at compile-time :/
+impl ShortWeierstrass for Embedwards25519 {
+  type FieldElement = FieldElement;
+  const A: FieldElement = FieldElement(DalekScalar::from_bits(hex_literal::hex!(
+    "ead3f55c1a631258d69cf7a2def9de1400000000000000000000000000000010"
+  )));
+  const B: FieldElement = FieldElement(DalekScalar::from_bits(hex_literal::hex!(
+    "5f07603a853f20370b682036210d463e64903a23ea669d07ca26cfc13f594209"
+  )));
+  const PRIME_ORDER: bool = true;
+  const GENERATOR: Affine<Self> = Affine::from_xy_unchecked(
+    FieldElement::ONE,
+    FieldElement(DalekScalar::from_bits(hex_literal::hex!(
+      "2e4118080a484a3dfbafe2199a0e36b7193581d676c0dadfa376b0265616020c"
+    ))),
+  );
+  type Scalar = Scalar;
+
+  type Repr = [u8; 32];
+  // Use an all-zero encoding for the identity as `0` isn't the `x` coordinate of an on-curve point
+  const IDENTITY: [u8; 32] = [0; 32];
+  fn encode_compressed(x: Self::FieldElement, odd_y: Choice) -> Self::Repr {
+    // The LE `x` coordinate, with if `y` is odd in the unused 256th bit
+    let mut res = [0; 32];
+    res.as_mut().copy_from_slice(x.to_repr().as_ref());
+    res[31] |= odd_y.unwrap_u8() << 7;
+    res
+  }
+  fn decode_compressed(bytes: &Self::Repr) -> (<Self::FieldElement as PrimeField>::Repr, Choice) {
+    // Extract and clear the sign bit
+    let mut bytes = *bytes;
+    let odd_y = Choice::from(bytes[31] >> 7);
+    bytes[31] &= u8::MAX >> 1;
+
+    // Copy from the point's representation to the field's
+    let mut repr = <Self::FieldElement as PrimeField>::Repr::default();
+    repr.as_mut().copy_from_slice(&bytes);
+
+    (repr, odd_y)
+  }
+  // No points have a torsion element as this a prime-order curve
+  fn has_torsion_element(_point: Projective<Self>) -> Choice {
+    0.into()
+  }
+}
+
+pub type Point = Projective<Embedwards25519>;
+
+impl ciphersuite::Ciphersuite for Embedwards25519 {
+  type F = Scalar;
+  type G = Point;
+  type H = blake2::Blake2b512;
+
+  const ID: &'static [u8] = b"embedwards25519";
+
+  fn generator() -> Self::G {
+    Point::generator()
+  }
+
+  /// `hash_to_F` is implemented with a naive concatenation of the `dst` and `data`, allowing
+  /// transposition between the two. This means `dst: b"abc", data: b"def"`, will produce the same
+  /// scalar as `dst: "abcdef", data: b""`. Please use carefully, not letting `dst` valuess be
+  /// substrings of each other.
+  fn hash_to_F(dst: &[u8], data: &[u8]) -> Self::F {
+    use blake2::Digest;
+    <Scalar as FromUniformBytes<64>>::from_uniform_bytes(
+      &Self::H::digest([dst, data].concat()).into(),
+    )
+  }
+
+  // We override the provided impl, which compares against the reserialization, because
+  // we already require canonicity
+  #[cfg(feature = "alloc")]
+  #[allow(non_snake_case)]
+  fn read_G<R: Read>(reader: &mut R) -> io::Result<Self::G> {
+    use ciphersuite::group::GroupEncoding;
+
+    let mut encoding = <Self::G as GroupEncoding>::Repr::default();
+    reader.read_exact(encoding.as_mut())?;
+
+    let point = Option::<Self::G>::from(Self::G::from_bytes(&encoding))
+      .ok_or_else(|| io::Error::other("invalid point"))?;
+    Ok(point)
+  }
+}
+
+#[cfg(feature = "alloc")]
+impl generalized_bulletproofs_ec_gadgets::DiscreteLogParameter for Embedwards25519 {
+  type ScalarBits = generic_array::typenum::U<{ <Scalar as PrimeField>::NUM_BITS as usize }>;
+}
+
+#[test]
+fn test_curve() {
+  ff_group_tests::group::test_prime_group_bits::<_, Point>(&mut rand_core::OsRng);
+}
+
+#[test]
+fn generator() {
+  use ciphersuite::group::{Group, GroupEncoding};
+  assert_eq!(
+    Point::generator(),
+    Point::from_bytes(&hex_literal::hex!(
+      "0100000000000000000000000000000000000000000000000000000000000000"
+    ))
+    .unwrap()
+  );
+}
+
+#[test]
+fn zero_x_is_off_curve() {
+  assert!(bool::from(
+    Affine::<Embedwards25519>::decompress(FieldElement::ZERO, 1.into()).is_none()
+  ));
+}
+
+// Checks random won't infinitely loop
+#[test]
+fn random() {
+  use ciphersuite::group::Group;
+  Point::random(&mut rand_core::OsRng);
+}