Google's Audio CAPTCHA Falls To Automated Attack

SkiifGeek writes "Early in March, Wintercore Labs published proof of a generic approach to defeating audio CAPTCHAs, using Google's as the case study for their demonstration. With claims of over 90% success rate and expectations that this can be significantly improved with the right mix of filtering algorithms, the in-house tool remains unreleased. But it shouldn't take long for other developers to create their own tools and start targeting not only Google, but other sites that use audio CAPTCHAs for the vision-impaired. It isn't the first time that major sites (significantly major webmail providers) have had their CAPTCHAs broken, but it is the first reporting of defeating an audio CAPTCHA using a generic software approach. News about the discovery is slowly starting to spread."

More easier to detect a bot

[Anonymous Coward]

It's more easier to detect a bot using audio captcha because a high number of simultaneous impaired users from a single IP is much less likely to happen than regular captcha.

probably borrowing from IVR technology

[revlayle]

some of the advanced IVR solutions (Interactive Voice Response... for like customer support or paying bills on the phone) can pick out numbers and words pretty well even under some noise conditions. so I am not totally surprised that this cracked the audio CAPTCHA.

It was bound to happen

[Half-pint HAL]

Right from the start it was clear that audio captchas were theoretically easier to break than visual ones.

An image captcha is designed to require a mixture of perception and thought, but an audio one has to rely on pure perception, because it's temporary. You hear it then it's gone: you can't analyse it. This makes it infinitely less complicated that a video one.

It's only because of low uptake that it's taken so long for a true proof-of-concept attack.

HAL.

Re:Adapt the visual approach

[carlvlad]

I hardly ever fail CAPTCHAs before, but ever since RapidShare implements their new CAPTCHAs it made me realized of how many more people suffered through annoyance of this. Kinda ironic though, it was supposed to weed out non-human. Reminds me of the Dilbert strip where PHB is considered the first human to fail the Turing Test.

captchas are obsolete

[Anonymous Coward]

do something else. show me a picture of an object and ask me (in a multiple-choice test?) what it is...a tree, a car, a house, a flower, whatever.

and for the sight-impaired, how about a read description or definition of something? "this thing is the entrance to a house or a room" => door

come on, webdesigner, it's not that hard to abandon those old and, above all, ANNOYING captchas

Are all audio CAPTCHAs failures?

[MrCrassic]

So given that (I assume) all audio CAPTCHAs have the same problem (i.e., the numbers and clearer voices can easily be found using audio analysis), does that mean that all audio-based CAPTCHAs are bound to fail?

CAPTCHA technology has a long fight ahead

[Thornburg]

CAPTCHA technology is going to have a very difficult time over the next few years. Finding tasks (which can be implemented on standard computer systems and transmitted over the internet) that are trivial for humans but exceedingly difficult for computers is going to be rough.

This is especially true because the computer doesn't need a 100% success rate to effectively "break" the CAPTCHA. Heck, if the CAPTCHA gives you 3 tries before rejecting you, then a 30% success rate = fully broken.

For right now, they are still working their way through tasks that CAN be easy for computers, but no one has bothered with yet. This means that breaking the CAPTCHA is simply a matter of writing and tuning some algorithms.

I think the next step (but not the be-all/end-all of CAPTCHAs) will be a parallel approach. Give the person 4 visual or auditory CAPTCHAs, and require them to successfully solve 3 out of 4 to pass, preferably with some kind of relational puzzle regarding the answers, or at least a simple question...

EXAMPLE:

A typical obfuscated-word type CAPTCHA in 4-way parallel, the four words are KITTEN PIGLET PUPPY TOASTER, then you are asked, "Which of these is NOT a baby animal?"

Obviously this technique requires either a complete solution from the user (4/4 words correct), or requires the system to reveal the answers, which could lead to an attack based upon a dictionary-building system, which would require a massive database size (and/or a frequently updated database) to prevent.

There is room for some really innovative work in this field, as the battle will probably continue for quite a while, with ever-increasing computational speed making it more difficult.

In the end, it comes down to this:

There is nothing non-biological that every human can do but no computer can do.

Paid humans beat captchas

[davidwr]

Paying 3rd-world human beings usually gets past captchas.

A partial solution is to limit the services you offer based on how well you know them. Anonymous? Offer very limited services.
Anonymous but tied to an existing email address? Offer a bit more.
Authenticated by credit card, which could be stolen? Offer a bit more.
Authenticated by PO box? Offer more.
Authenticated by street address, driver's license number, and a notary? Assume they are legit, you can always sue the notary if they aren't.

Authenticated against an email address that you know has X degree of authentication? Treat them like they have X degree of authentication.

For email, USENET, and IM services, offer a relatively low limit on outgoing data for free services, charge $1/year to a credit card or checking account OR require a copy of a state-issued ID to remove the limit. Watch for multiple free accounts from the same person and give them a collective limit the same as a single free account.

Isnt this a good sign?

[Anonymous Coward]

Captcha (and Recaptcha) were used as tools since machines were not smart enough to crack distorted charecters. The fact that they are able to do so now is great news! Now these techniques can be used in improving existing image recognition tools... provided there's a way to obtain access to the spammers toolbox.

Am looking forward to the first TRUE bot to post comments here...

Re:Adapt the approach

[asCii88]

I think they should make captchas that require some kind of rational thinking. For example they could say "Write the third word of this sentence" And of course the answer should be "third". That's lot more difficult to be cracked and if you look at the infinite variations you can make to it, you can say it's uncrackable until they can make a bot that understands natural speech.

Re:captchas are obsolete

[mapkinase]

Multiple choice are just silly. If there are 5 choices, in about ~5 tries the robot will pass the protected entrance.

Re:It was bound to happen

[firewrought]

An image captcha is designed to require a mixture of perception and thought, but an audio one has to rely on pure perception, because it's temporary.

I think your explanation is missing something, but I can't quite put my finger on what it is. Maybe it would be more accurate to say that audio captcha are simpler to process because (1) researches can't pump as much information thru the ears as they can thru the eyes [sensorary bandwidth is different] and (2) there's not a whole lot we can do to obfuscate a sound stream [as opposed to an image which can have lots of unused parts where we can throw whatever noise we want to].

Note that you could make audio captcha require thought. Someone else mentioned asking questions that require specific answers, but that might be difficult to automate: you would need a corpus with thousands of questions that require one-word answers. Perhaps the best way to do that would be to get your hands on a database of crossword puzzles and randomly generate questions like "3 letter word for pet, beginning with 'C'". Exclude words that don't appear in a modestly-sized dictionary, exclude certain obscure words that appear in crosswords way more than normal English (like "adit"--a mine entrance), and make it easy for people to get a new clue if they're having trouble guessing the current one.