Description
int
mcrypt_get_iv_size ( string cipher, string mode )
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
or one of "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.
It is more useful to use the mcrypt_enc_get_iv_size()
function as this uses the resource returned by
mcrypt_module_open().
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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See also
mcrypt_get_block_size(),
mcrypt_enc_get_iv_size() and
mcrypt_create_iv().
