message: NO-TICKET: Hold signature error as string.
  This solves lack of useful traits in `SignatureError` in recent
  ed25519-dalek crate.
diff: @@ -10,11 +10,11 @@ use thiserror::Error;
  pub type Result<T> = result::Result<T, Error>;
  /// Cryptographic errors.
  -#[derive(Debug, Error)]
  +#[derive(Clone, PartialEq, Debug, Error)]
  pub enum Error {
  /// Error resulting from creating or using asymmetric key types.
  #[error("asymmetric key error: {0}")]
  - AsymmetricKey(SignatureError),
  + AsymmetricKey(String),
  /// Error resulting when decoding a type from a hex-encoded representation.
  #[error("parsing from hex: {0}")]
  FromHex(#[from] FromHexError),
  @@ -31,7 +31,7 @@ pub enum Error {
  impl From<SignatureError> for Error {
  fn from(signature_error: SignatureError) -> Self {
  - Error::AsymmetricKey(signature_error)
  + Error::AsymmetricKey(signature_error.to_string())
  }
  }
  