bool openssl_pkey_export ( mixed $key , string &$out [, string $passphrase [, array $configargs ]] )
openssl_pkey_export() exports key as a PEM encoded string and stores it into out (which is passed by reference). Note: You need to have a valid openssl.cnf installed for this function to operate correctly. See the notes under the installation section for more information.
Returns TRUE on success or FALSE on failure.