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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` (string cipher, string mode)`

``int mcrypt_get_iv_size` (resource td)`

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

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 algorithm specified.

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