code: def _write_private_key_file(self, tag, filename, data, password=None):
          
          f = open(filename, 'w', 0600)
          # grrr... the mode doesn't always take hold
          os.chmod(filename, 0600)
          self._write_private_key(tag, f, data, password)
          f.close()
docs: Write an SSH2-format private key file in a form that can be read by
          ssh or openssh.  If no password is given, the key is written in
          a trivially-encoded format (base64) which is completely insecure.  If
          a password is given, DES-EDE3-CBC is used.
  
          @param tag: C{"RSA"} or C{"DSA"}, the tag used to mark the data block.
          @type tag: str
          @param filename: name of the file to write.
          @type filename: str
          @param data: data blob that makes up the private key.
          @type data: str
          @param password: an optional password to use to encrypt the file.
          @type password: str
  
          @raise IOError: if there was an error writing the file.