int mcrypt_get_iv_size(string $cipher, string $mode)
This function has been DEPRECATED as of PHP 7.1.0. Relying on this function is highly discouraged.
Gets the size of the IV belonging to a specific
It is more useful to use the mcrypt_enc_get_iv_size() function as this uses the resource returned by mcrypt_module_open().
Returns the size of the Initialization Vector (IV) in bytes. On error the function returns
FALSE. If the IV is ignored in the specified cipher/mode combination zero is returned.
- string $cipher: One of the
MCRYPT_ciphernameconstants, or the name of the algorithm as string.
- string $mode: One of the
MCRYPT_MODE_modenameconstants, or one of the following strings: "ecb", "cbc", "cfb", "ofb", "nofb" or "stream".
The IV is ignored in ECB mode as this mode does not require it. You will need to have the same IV (think: starting point) both at encryption and decryption stages, otherwise your encryption will fail.
Example #1 mcrypt_get_iv_size() Example
echo mcrypt_get_iv_size(MCRYPT_CAST_256, MCRYPT_MODE_CFB) . "\n";
echo mcrypt_get_iv_size('des', 'ecb') . "\n";