php man page for mcrypt_get_iv_size

MCRYPT_GET_IV_SIZE(3)							 1						     MCRYPT_GET_IV_SIZE(3)

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

SYNOPSIS
       int mcrypt_get_iv_size (string  $cipher, string	$mode)

DESCRIPTION
	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(3) function as this uses the resource returned by mcrypt_module_open(3).

PARAMETERS
	      o $cipher
		-One of the MCRYPT_ciphername constants, or the name of the algorithm as string.

	      o $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.

RETURN VALUES
	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.

EXAMPLES
       Example #1

	      mcrypt_get_iv_size(3) Example

	      <?php
		  echo mcrypt_get_iv_size(MCRYPT_CAST_256, MCRYPT_MODE_CFB) . "
";

		  echo mcrypt_get_iv_size('des', 'ecb') . "
";
	      ?>

SEE ALSO
       mcrypt_get_block_size(3), mcrypt_enc_get_iv_size(3), mcrypt_create_iv(3).

PHP Documentation Group 												     MCRYPT_GET_IV_SIZE(3)