您可以使用phpseclib,这是一个纯PHP RSA实现:
<?PHP
include('Crypt/RSA.PHP');
$privatekey = file_get_contents('private.key');
$rsa = new Crypt_RSA();
$rsa->loadKey($privatekey);
$plaintext = new Math_BigInteger('aaaaaa');
echo $rsa->_exponentiate($plaintext)->toBytes();
?>