On Mon, 2007-04-09 at 16:27 +0200, Tijnema ! wrote: > > I think that we can conclude that a non-crackable CAPTCHA doesn't > exist, but also that there doesn't exist a real "hard to crack" > CAPTCHA. All current CAPTCHAs can be broken quite easy. MD5 can help > in some cases, but only if the CAPTCHA uses static > images/audio/video/etc. Just about your Audio CAPTCHA, you could use > MD5 to crack it, as the number has the same MD5 sum each time. Similar methods could be applied to sound as to images to distort the sound enough to make it difficult for speech recognition software to understand, but not so much that real humans couldn't understand it. At any rate, it could be enough to prevent md5 indexing... but then again, that would require the audio be mutated on each request, and enough audio be mutated to prevent md5 indexing based on partial signatures -- similar to how viruses are detected - this is especially important if using dictionary words since the sample space is so small (could always use sentences though) :) Cheers, Rob. -- .------------------------------------------------------------. | InterJinn Application Framework - http://www.interjinn.com | :------------------------------------------------------------: | An application and templating framework for PHP. Boasting | | a powerful, scalable system for accessing system services | | such as forms, properties, sessions, and caches. InterJinn | | also provides an extremely flexible architecture for | | creating re-usable components quickly and easily. | `------------------------------------------------------------' -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
