mcrypt_get_iv_size(3) [php man page]

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)

MDECRYPT_GENERIC(3)							 1						       MDECRYPT_GENERIC(3)

mdecrypt_generic - Decrypts data

SYNOPSIS

       string mdecrypt_generic (resource  $td, string  $data)

DESCRIPTION

	This  function	decrypts  data.  Note that the length of the returned string can in fact be longer than the unencrypted string, due to the
       padding of the data.

PARAMETERS

	      o $td
		- An encryption descriptor returned by mcrypt_module_open(3)

	      o $data
		- Encrypted data.

EXAMPLES

       Example #1

	      mdecrypt_generic(3) Example

	      <?php
		  /* Data */
		  $key = 'this is a very long key, even too long for the cipher';
		  $plain_text = 'very important data';

		  /* Open module, and create IV */
		  $td = mcrypt_module_open('des', '', 'ecb', '');
		  $key = substr($key, 0, mcrypt_enc_get_key_size($td));
		  $iv_size = mcrypt_enc_get_iv_size($td);
		  $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);

		  /* Initialize encryption handle */
		  if (mcrypt_generic_init($td, $key, $iv) != -1) {

		      /* Encrypt data */
		      $c_t = mcrypt_generic($td, $plain_text);
		      mcrypt_generic_deinit($td);

		      /* Reinitialize buffers for decryption */
		      mcrypt_generic_init($td, $key, $iv);
		      $p_t = mdecrypt_generic($td, $c_t);

		      /* Clean up */
		      mcrypt_generic_deinit($td);
		      mcrypt_module_close($td);
		  }

		  if (strncmp($p_t, $plain_text, strlen($plain_text)) == 0) {
		      echo "ok
";
		  } else {
		      echo "error
";
		  }
	      ?>

	The example above shows how to check if the data before the encryption is the same as the data after the decryption. It is very  important
       to reinitialize the encryption buffer with mcrypt_generic_init(3) before you try to decrypt the data.

	The  decryption  handle  should always be initialized with mcrypt_generic_init(3) with a key and an IV before calling this function. Where
       the encryption is done, you should free the encryption buffers by calling mcrypt_generic_deinit(3). See mcrypt_module_open(3) for an  exam-
       ple.

SEE ALSO

       mcrypt_generic(3), mcrypt_generic_init(3), mcrypt_generic_deinit(3).

PHP Documentation Group 												       MDECRYPT_GENERIC(3)