(PHP 4 >= 4.0.2, PHP 5, PHP 7 < 7.2.0, PECL mcrypt >= 1.0.0)
mcrypt_get_iv_size — Returns the size of the IV belonging to a specific cipher/mode combination
This function has been DEPRECATED as of PHP 7.1.0 and REMOVED as of PHP 7.2.0. Relying on this function is highly discouraged.
mcrypt_get_iv_size ( string $cipher , string $mode ) : int
Gets the size of the IV belonging to a specific cipher
/mode
combination.
It is more useful to use the mcrypt_enc_get_iv_size() function as this uses the resource returned by mcrypt_module_open().
cipher
One of the MCRYPT_ciphername
constants, or the name of the algorithm as string.
mode
One of the MCRYPT_MODE_modename
constants, 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.
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.
Example #1 mcrypt_get_iv_size() Example
<?php echo mcrypt_get_iv_size(MCRYPT_CAST_256, MCRYPT_MODE_CFB) . "\n"; echo mcrypt_get_iv_size('des', 'ecb') . "\n"; ?>
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https://www.php.net/manual/en/function.mcrypt-get-iv-size.php