PHP/Utility Function/mcrypt enc get key size

Symmetric Decryption

   <source lang="html4strict">

<?

   srand((double)microtime( )*1000000 );
   $td = mcrypt_module_open(MCRYPT_RIJNDAEL_256, "", MCRYPT_MODE_CFB, "");
   $iv = mcrypt_create_iv(mcrypt_enc_get_iv_size($td), MCRYPT_RAND);
   $ks = mcrypt_enc_get_key_size($td);
   $key = substr(sha1("Your Secret Key Here"), 0, $ks);
   mcrypt_generic_init($td, $key, $iv);
   $ciphertext = mcrypt_generic($td, "This is very important data");
   mcrypt_generic_deinit($td);
   mcrypt_generic_init($td, $key, $iv);
   $plaintext = mdecrypt_generic($td, $ciphertext);
   mcrypt_generic_deinit($td);
   mcrypt_module_close($td);
   print $iv . "\n";
   print trim($ciphertext) . "\n";
   print trim($plaintext) . "\n";

?>

 </source>