message: utilise SEED_LENGTH in FakeMMM as in ed25519.rs
diff: @@ -8,7 +8,7 @@ use rand_core::{CryptoRng, RngCore};
  pub struct FakeMMM;
  #[derive(Clone)]
  -pub struct Priv([u8; ed25519::PRIVATE_KEY_LENGTH]);
  +pub struct Priv([u8; ed25519::SEED_LENGTH]);
  #[derive(Clone, PartialEq, Eq, Hash)]
  pub struct Pub([u8; ed25519::PUBLIC_KEY_LENGTH]);
  @@ -39,7 +39,7 @@ impl AsymmetricKey for FakeMMM {
  type Public = Pub;
  fn generate<T: RngCore + CryptoRng>(mut rng: T) -> Priv {
  - let mut priv_bytes = [0u8; ed25519::PRIVATE_KEY_LENGTH];
  + let mut priv_bytes = [0u8; ed25519::SEED_LENGTH];
  rng.fill_bytes(&mut priv_bytes);
  Priv(priv_bytes)
  }
  @@ -50,11 +50,11 @@ impl AsymmetricKey for FakeMMM {
  }
  fn secret_from_binary(data: &[u8]) -> Result<Priv, SecretKeyError> {
  - if data.len() != ed25519::PRIVATE_KEY_LENGTH {
  + if data.len() != ed25519::SEED_LENGTH {
  return Err(SecretKeyError::SizeInvalid);
  }
  - let mut buf = [0; ed25519::PRIVATE_KEY_LENGTH];
  - buf[0..ed25519::PRIVATE_KEY_LENGTH].clone_from_slice(data);
  + let mut buf = [0; ed25519::SEED_LENGTH];
  + buf[0..ed25519::SEED_LENGTH].clone_from_slice(data);
  Ok(Priv(buf))
  }
  fn public_from_binary(data: &[u8]) -> Result<Pub, PublicKeyError> {
  