note 21571 added to function.md5

Reply to dgolesny@avo-web.de's comment on 15-Feb-2002: To be very security conscious, using your script as written isn't a good idea either. You have the following: function generatekey($count) { mt_srand((double)microtime()*1000000); $key = ""; for ($i=0; $i<$count; $i++) { $c = mt_rand(0,2); if ($c==0) { $key .= chr(mt_rand(65,90)); } elseif ($c==1) { $key .= chr(mt_rand(97,122)); } else { $key .= mt_rand(0,9); } } return $key; } The problem is with how you use $c. $c is either 0, 1, or 2, which is how you decide which class of character to randomly append to $key. You equally weighted the choices made by $c. Partitioning up the possible choices like this means that any character going into the password is chosen from less than half of the possible choices, and sometimes less than 1/6th of the possible choices (when $c = 2). One third of the time, $c will equal 2. This means a full third of any generated password will consist of the numerals 0 to 9. In other words, there is a 33% chance any character in a password is one of ten characters instead of any character being evenly distributed over a possible 62. Patterns like this make attackers happy because they're easy to exploit and even easier to search. Instead of a password of length n being one of 62^n possibilities, it will be one of [26^(n/3)] * [26^(n/3)] * [10^(n/3)] (if I'm thinking correctly). For a nine character password, the first scheme gives you 13537086546263552 (1.35 * 10^16) combinations, but yours only gives 308915776000 (3.08 * 10^11) combinations, which is about .001% of the possible keyspace. In other words, if it took a computer 24 hours to check the whole keyspace of n-character passwords as defined above, the keyspace generated by your algorithm could be brute-forced in under one second. To fix this, randomly generate a number between 1 and 62 inclusive and translate that to a character to append. Even better, include punctuation as well. The more possible characters in a password, the harder it will be to break and the more possible combinations there are of those characters the better. -- http://www.php.net/manual/en/function.md5.php http://master.php.net/manage/user-notes.php?action=edit+21571 http://master.php.net/manage/user-notes.php?action=delete+21571 http://master.php.net/manage/user-notes.php?action=reject+21571