text: """
  ECDSA key management
  """
  
  from cryptography.hazmat.backends import default_backend
  from cryptography.hazmat.primitives import serialization
  from cryptography.hazmat.primitives.asymmetric import ed25519
  
  from .general import KeyClass
  
  
  class Ed25519UsageError(Exception):
      pass
  
  
  class Ed25519Public(KeyClass):
      def __init__(self, key):
          self.key = key
  
      def shortname(self):
          return "ed25519"
  
      def _unsupported(self, name):
          raise Ed25519UsageError("Operation {} requires private key".format(name))
  
      def _get_public(self):
          return self.key
  
      def get_public_bytes(self):
          # The key is embedded into MBUboot in "SubjectPublicKeyInfo" format
          return self._get_public().public_bytes(
                  encoding=serialization.Encoding.DER,
                  format=serialization.PublicFormat.SubjectPublicKeyInfo)
  
      def export_private(self, path, passwd=None):
          self._unsupported('export_private')
  
      def export_public(self, path):
          """Write the public key to the given file."""
          pem = self._get_public().public_bytes(
                  encoding=serialization.Encoding.PEM,
                  format=serialization.PublicFormat.SubjectPublicKeyInfo)
          with open(path, 'wb') as f:
              f.write(pem)
  
      def sig_type(self):
          return "ED25519"
  
      def sig_tlv(self):
          return "ED25519"
  
      def sig_len(self):
          return 64
  
  
  class Ed25519(Ed25519Public):
      """
      Wrapper around an ECDSA private key.
      """
  
      def __init__(self, key):
          """key should be an instance of EllipticCurvePrivateKey"""
          self.key = key
  
      @staticmethod
      def generate():
          pk = ed25519.Ed25519PrivateKey.generate()
          return Ed25519(pk)
  
      def _get_public(self):
          return self.key.public_key()
  
      def export_private(self, path, passwd=None):
          """
          Write the private key to the given file, protecting it with the
          optional password.
          """
          if passwd is None:
              enc = serialization.NoEncryption()
          else:
              enc = serialization.BestAvailableEncryption(passwd)
          pem = self.key.private_bytes(
                  encoding=serialization.Encoding.PEM,
                  format=serialization.PrivateFormat.PKCS8,
                  encryption_algorithm=enc)
          with open(path, 'wb') as f:
              f.write(pem)
  
      def sign_digest(self, digest):
          """Return the actual signature"""
          return self.key.sign(data=digest)
  
      def verify_digest(self, signature, digest):
          """Verify that signature is valid for given digest"""
          k = self.key
          if isinstance(self.key, ed25519.Ed25519PrivateKey):
              k = self.key.public_key()
          return k.verify(signature=signature, data=digest)
  