note 40434 added to function.mcrypt-create-iv

It is important to note that all cipher modes except ecb require the same IV to be used in decryption as was used in encryption. You need to pass the key *and* the IV to your decrypt function. Initializing a new IV in the decrypt routine will not work. Since, "you even can send [the IV] along with your ciphertext without loosing security," a nice way to handle this is to prepend your IV to your ciphertext. Since the IV is fixed-width, you can then easily recover the IV and original ciphertext using mcrypt_get_iv_size() and substr(). Here is an example: <?PHP function my_encrypt($string,$key) { srand((double) microtime() * 1000000); //for sake of MCRYPT_RAND $key = md5($key); //to improve variance /* Open module, and create IV */ $td = mcrypt_module_open('des', '','cfb', ''); $key = substr($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, $string); mcrypt_generic_deinit($td); mcrypt_module_close($td); $c_t = $iv.$c_t; return $c_t; } //end if } function my_decrypt($string,$key) { $key = md5($key); //to improve variance /* Open module, and create IV */ $td = mcrypt_module_open('des', '','cfb', ''); $key = substr($key, 0, mcrypt_enc_get_key_size($td)); $iv_size = mcrypt_enc_get_iv_size($td); $iv = substr($string,0,$iv_size); $string = substr($string,$iv_size); /* Initialize encryption handle */ if (mcrypt_generic_init($td, $key, $iv) != -1) { /* Encrypt data */ $c_t = mdecrypt_generic($td, $string); mcrypt_generic_deinit($td); mcrypt_module_close($td); return $c_t; } //end if } // to test: //print my_decrypt(my_encrypt("Hello, world.","foo"),"foo"); ?> ---- Manual Page -- http://www.php.net/manual/en/function.mcrypt-create-iv.php Edit -- http://master.php.net/manage/user-notes.php?action=edit+40434 Delete -- http://master.php.net/manage/user-notes.php?action=delete+40434&report=yes Reject -- http://master.php.net/manage/user-notes.php?action=reject+40434&report=yes Search -- http://master.php.net/manage/user-notes.php