def decrypt(data)
      raise NoPrivateKeyError, "Private key file: #{private_key_file}" unless private?
      
      decrypted_data = data.unpack('m')[0]
      private_rsa.private_decrypt(decrypted_data)
    end
def decrypt(data)
      raise NoPrivateKeyError, "Private key file: #{private_key_file}" unless private?
      
      decrypted_data = data.unpack('m')[0]
      private_rsa.private_decrypt(decrypted_data)
    end
Decrypts the given data. If no private key file has been specified, then
 a NoPrivateKeyError will be raised.