Murray @ PlanetThoughtful wrote:
The app in question was storing the md5 value of 4-digit PINs in the background database, and the owners of the app were quietly confident that this meant the PINs were 'encrypted' and 'secure'.
Amazing. Thanks for sharing that. It's a great example. :-)
Of course, there are only 10,000 possible PIN values between 0000 and 9999, regardless of whether or not they're stored in plaintext or md5 hashed form, and I guess it took me less than 15 minutes to build a reference table of all md5 hash values for the possible plaintext PINs and therefore effortlessly retrieve the plaintext PIN values from their table.
There are efforts to create these types of tables for arbitrary strings: http://md5.rednoize.com/ Of course, it's worth noting that these methods aren't reversing MD5.
Md5 is a very handy way of 'securing' [1] password information, but only when the plaintext value offers enough possible variation in length and / or value to make building a 'possible variations' lookup table a difficult proposition.
Exactly, and this is why it's a good practice to use a seed when you generate MD5s for passwords.
Thanks again for the story, frightening as it was. :-) Chris -- Chris Shiflett Brain Bulb, The PHP Consultancy http://brainbulb.com/ -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
