serai/crypto/ed448/src/ciphersuite.rs

use prime_field::subtle::CtOption;

use sha3::{
  digest::{
    typenum::U114, core_api::BlockSizeUser, Update, Output, OutputSizeUser, FixedOutput,
    ExtendableOutput, XofReader, HashMarker,
  },
  Shake256,
};

use ciphersuite::{group::GroupEncoding, Id, WithPreferredHash, GroupCanonicalEncoding};

use crate::Point;

/// Shake256, fixed to a 114-byte output, as used by Ed448.
#[derive(Clone, Default)]
pub struct Shake256_114(Shake256);
impl BlockSizeUser for Shake256_114 {
  type BlockSize = <Shake256 as BlockSizeUser>::BlockSize;
  fn block_size() -> usize {
    Shake256::block_size()
  }
}
impl OutputSizeUser for Shake256_114 {
  type OutputSize = U114;
  fn output_size() -> usize {
    114
  }
}
impl Update for Shake256_114 {
  fn update(&mut self, data: &[u8]) {
    self.0.update(data);
  }
  fn chain(mut self, data: impl AsRef<[u8]>) -> Self {
    Update::update(&mut self, data.as_ref());
    self
  }
}
impl FixedOutput for Shake256_114 {
  fn finalize_fixed(self) -> Output<Self> {
    let mut res = Default::default();
    FixedOutput::finalize_into(self, &mut res);
    res
  }
  fn finalize_into(self, out: &mut Output<Self>) {
    let mut reader = self.0.finalize_xof();
    reader.read(out);
  }
}
impl HashMarker for Shake256_114 {}

impl Id for Point {
  const ID: &[u8] = b"ed448";
}
impl WithPreferredHash for Point {
  type H = Shake256_114;
}
impl GroupCanonicalEncoding for Point {
  fn from_canonical_bytes(bytes: &<Self::G as GroupEncoding>::Repr) -> CtOption<Self::G> {
    Self::G::from_bytes(bytes)
  }
}