(PHP 4 >= 4.0.2, PHP 5, PHP 7)
mcrypt_enc_get_iv_size — Returns the size of the IV of the opened algorithm
$td
)This function returns the size of the IV of the algorithm specified by the encryption descriptor in bytes. An IV is used in cbc, cfb and ofb modes, and in some algorithms in stream mode.
tdThe encryption descriptor.
Returns the size of the IV, or 0 if the IV is ignored by the algorithm.