mcrypt_generic_init(3) [php man page]

MCRYPT_GENERIC_INIT(3)							 1						    MCRYPT_GENERIC_INIT(3)

mcrypt_generic_init - This function initializes all buffers needed for encryption

SYNOPSIS

       int mcrypt_generic_init (resource  $td, string  $key, string  $iv)

DESCRIPTION

	You need to call this function before every call to mcrypt_generic(3) or mdecrypt_generic(3).

PARAMETERS

	      o $td
		- The encryption descriptor.

	      o $key
		- The maximum length of the key should be the one obtained by calling mcrypt_enc_get_key_size(3) and every value smaller than this
		is legal.

	      o $iv
		-  The	IV  should  normally  have  the  size  of  the	algorithms  block  size,  but  you  must  obtain  the  size   by   calling
		mcrypt_enc_get_iv_size(3).  IV is ignored in ECB. IV MUST exist in CFB, CBC, STREAM, nOFB and OFB modes. It needs to be random and
		unique (but not secret). The same IV must be used for encryption/decryption. If you do not want to use it you  should  set  it	to
		zeros, but this is not recommended.

RETURN VALUES

	The  function  returns	a negative value on error: -3 when the key length was incorrect, -4 when there was a memory allocation problem and
       any other return value is an unknown error. If an error occurs a warning will be displayed accordingly.	FALSE  is  returned  if  incorrect
       parameters were passed.

SEE ALSO

       mcrypt_module_open(3).

PHP Documentation Group 												    MCRYPT_GENERIC_INIT(3)

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)