code: def _prepare(self, serialized_obj):
          '''
          Prepare the object to be sent over the untrusted channel.
          '''
          # generating a nonce
          nonce = nacl.utils.random(nacl.secret.SecretBox.NONCE_SIZE)
          # encrypting using the nonce
          encrypted = self.__safe.encrypt(serialized_obj, nonce)
          # sign the message
          signed = self.__signing_key.sign(encrypted)
          return signef _prepare(self, serialized_obj):
          '''
          Prepare the object to be sent over the untrusted channel.
          '''
          # generating a nonce
          nonce = nacl.utils.random(nacl.secret.SecretBox.NONCE_SIZE)
          # encrypting using the nonce
          encrypted = self.__safe.encrypt(serialized_obj, nonce)
          # sign the message
          signed = self.__signing_key.sign(encrypted)
          return signed
docs: Prepare the object to be sent over the untrusted channel.