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)

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)