mcrypt_create_iv - why so slow?

Hi folks, This code: <?php $iv = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_CBC), MCRYPT_DEV_RANDOM); var_dump($iv); Takes just over a minute to run on my laptop and roughly 45 seconds on a capable server, any idea why? time php test-iv.php string(32) "????'???H??y?PJ?U?1O;6???ѧ" real 0m44.917s user 0m0.024s sys 0m0.036s Also, I've noticed the mcrypt_encypt & mcrypt_decrypt complain with The IV parameter must be as long as the blocksize when not using mcrypt_create_iv, however, if the value of the IV parameter is consistent in both calls, the decryption seems to succeed despite the warning. So wondering: * can the call to mcrypt_create_iv be sped up * is there an alternative (faster) way to create a proper iv * how big a risk is it to 'ride dirty' here and not use mcrypt_create_iv thanks, -nathan