'Write a new private key out to a new file, encrypted using the given
passphrase.  Return the path to the new file.'

def _write_encrypted_pem(self, passphrase):

    key = PKey()
    key.generate_key(TYPE_RSA, 128)
    pemFile = self.mktemp()
    fObj = open(pemFile, 'w')
    pem = dump_privatekey(FILETYPE_PEM, key, 'blowfish', passphrase)
    fObj.write(pem.decode('ascii'))
    fObj.close()
    return pemFile
