note 94125 added to function.mcrypt-decrypt

kooktroop's example (09-Jul-2004) may be a bit misleading. Using a random IV for encryption, then another random IV for decryption? If you run it, it works! That's because ECB doesn't use an IV. For modes that do use one you need the same one for encryption and decryption. For example, Rijndael-256 (aka AES-256) and CFB: <?php $text = "The quick brown fox jumps over the lazy dog."; $key = "haseveryletter"; $iv = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_CFB), MCRYPT_RAND); $encrypted = mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $key, $text, MCRYPT_MODE_CFB, $iv); // create a new IV $newiv = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_CFB), MCRYPT_RAND); $corrupt = mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $key, $encrypted, MCRYPT_MODE_CFB, $newiv); echo $corrupt; // [binary junk...]he lazy dog $good = mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $key, $encrypted, MCRYPT_MODE_CFB, $iv); echo $good; // The quick brown fox jumps over the lazy dog ?> Rijndael can sync up on each block so only the first one (here, 256 bits = 32 characters long) will be corrupted. Not necessarily true for other algorithms... ---- Server IP: 192.41.40.227 Probable Submitter: 69.166.47.131 ---- Manual Page -- http://www.php.net/manual/en/function.mcrypt-decrypt.php Edit -- https://master.php.net/note/edit/94125 Del: integrated -- https://master.php.net/note/delete/94125/integrated Del: useless -- https://master.php.net/note/delete/94125/useless Del: bad code -- https://master.php.net/note/delete/94125/bad+code Del: spam -- https://master.php.net/note/delete/94125/spam Del: non-english -- https://master.php.net/note/delete/94125/non-english Del: in docs -- https://master.php.net/note/delete/94125/in+docs Del: other reasons-- https://master.php.net/note/delete/94125 Reject -- https://master.php.net/note/reject/94125 Search -- https://master.php.net/manage/user-notes.php