docs: def decrypt(self, ciphertext):
          """Have the operator decrypt a message."""
  
          # Separate keys from message.
          enc_key = ciphertext[:3]
          message = ciphertext[3:-3]
          grundstellung = ciphertext[-3:]
  
          # Decrypt message key.
          self.machine.set_display(grundstellung)
          msg_key = self.machine.process_text(enc_key)
          # Decrpyt message.
          self.machine.set_display(msg_key)
          return self.machine.process_text(message)