At 2:30 PM -0700 4/3/07, jochem wrote:
Since you are asking for review: this audio captcha is almost certainly
easily breakable.
Tijnema is right with most of his comments, open source voice recognition
software (the code he pointed to like spynx) will break this.
I disagree with his point 3) below, obfuscating the speech with different
bitrates etc. will in my opinion not work.
How do I know? Unfortunately i do not have the time to properly test it, but
I wrote a devoicecaptcha script to break the voice captchas of microsoft,
google and paypal. You can download the code and test it with your code, see
http://vorm.net/captchas.
So unfortunately for you it will not work against spammers, but you are in
good company of people trying ;-).
Jochem:
Thanks for the link, article (very interesting), and advice.
The voice files that I am using could certainly be resolved by your
method -- they are simple and your solution is pretty straightforward.
However, I'm not convinced that all sound methodologies can be
resolved as simply as that. For example -- your method looks for
pauses/high points and then capsulizes segments for comparison
against known sounds. That's OK, but what if there is other meaning
in the sound?
I often wondered why simple CAPTCHA's like "Type the number seven
four three", or "What is the sum of two plus three?", or "Spell cat",
or "Spell two" wouldn't work? Certainly, one can create a routine
coupled a dB to randomly produce thousands of different combinations
of simple questions. Likewise, a sound file could be produced the
same way.
Perhaps I'm underestimating the capabilities of bots and
overestimating the abilities of humans. I suspect that the
distribution of both camps have an overlap and therein lies the
problem. The problem may not have a solution.
But to bring this back to my intent -- my intent here is to provide a
simple audio CAPTCHA that could be used by anyone to provide some
degree of protection for their personal use THAT would also be
accessible to screen readers. It's not foolproof, but it appears to
work in that regard.
Interesting discussion -- thanks for your perspective.
Cheers,
tedd
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