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# mcrypt_get_iv_size

(PHP 4 >= 4.0.2)

mcrypt_get_iv_size -- Returns the size of the IV belonging to a specific cipher/mode combination

## Description

int mcrypt_get_iv_size ( resource td)
int mcrypt_get_iv_size ( string cipher, string mode)

The first prototype is when linked against libmcrypt 2.2.x, the second when linked against libmcrypt 2.4.x or higher.

mcrypt_get_iv_size() returns the size of the Initialisation Vector (IV) in bytes. On error the function returns `FALSE`. If the IV is ignored in the specified cipher/mode combination zero is returned.

`cipher` is one of the MCRYPT_ciphername constants of the name of the algorithm as string.

`mode` is one of the MCRYPT_MODE_modename constants of one of "ecb", "cbc", "cfb", "ofb", "nofb" or "stream".

`td` is the resource that is returned by mcrypt_module_open().

Example 1. mcrypt_create_iv() example
    <?php
        $size = mcrypt_get_iv_size (MCRYPT_CAST_256, MCRYPT_MODE_CFB);

        $size = mcrypt_get_iv_size ('des', 'ecb');
    ?>

See also: mcrypt_create_iv()

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