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TextCAPTCHA: 180 million simple logic questions

textcaptcha.com

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Re: TextCAPTCHA: 180 million simple logic questions

#41

Post by tropin »

mseebach wrote: post #13
bjonathan wrote: post #8

Easy is not enough, Captcha need to be universal also. For non native english speakers: "Cheese, cat, mosquito, trousers, elbow and ant: how many body parts in the list?" or "Soup, dog, trousers, house, mosquito or pink: the colour is?"arent as easy as "3+1" or reCaptcha . Not everybody speak english on the interweb...

> Easy is not enough, Captcha need to be universal also. Perhaps on the long term, but solving the captcha problem for the english-speaking (or any language, for that matter) subset of the internet population is still a very worthwhile undertaking.

Yes, because capchas aren't alienating enough, we should also let non english speakers out of our non english written webs.

Re: TextCAPTCHA: 180 million simple logic questions

#43

Post by blahedo »

I've thought about this issue before (and proof-of-concepted a similar system, see http://www.blahedo.org/botblock/), and came to similar conclusions, but there's an important difference:

A crucial part of making this a successful anti-spam system is that it is a moving target. Every user of the system must be able to write their own questions. If that happens, the spammer's task is intractable. But if there is a central site serving these, it will be worth the spammers' while to just hardcode the patterns and write a little bit of logic to parse and answer them.

Now, there's a fair bit of interesting UI design in the question of "how do I get a non-programmer to write what is in essence a very small program". My proof of concept used some cute Perl-isms to basically construct a mini-language that was restricted enough that an inexperienced programmer could "script kiddie" their way through it, and I think this is the right general direction, but you'd need a fair amount of work to really make it accessible to the masses.

(Other crucial points that he gets right: it must be text based; it must have questions that hinge on natural language understanding but not be otherwise difficult; and it must have questions that are really question templates each of which can generate infinite numbers of question instances.)

Re: TextCAPTCHA: 180 million simple logic questions

#46

Post by azim »

I tried breaking this captcha. Here are some experimental results and mathematics:

By applying the mathematics from the Birthday Attack (http://en.wikipedia.org/wiki/Birthday_attack), If an attacker is able to solve 15.8 million of the 180 million captchas, there will be a 50% probability that the attacker can beat the captcha.

I tried refreshing the page 10 times, generating a total of 100 captchas. Out of those, I observed 8 arithmetic problems which I entered into and solved using Wolfram Alpha. That gives roughly the 15.8m/180m necessary to break the captcha with 50% probability.

At 50% probability, again going back to the Birthday Attack mathematics, an attacker would need roughly 16.8 thousand tries before expecting a collision with one they could break.

This probability will increase if an attacker is able to successfully reverse-engineer more patterns.

Edit: thinking about this more after MichaelGG's comment, I think my math is incorrect. Either way, point still stands that Wolfram Alpha can successfully solve 8% of the captchas and other patterns should be solvable by other means too.

Re: TextCAPTCHA: 180 million simple logic questions

#47

Post by MichaelGG »

azim wrote: post #46

I tried breaking this captcha. Here are some experimental results and mathematics: By applying the mathematics from the Birthday Attack ( http://en.wikipedia.org/wiki/Birthday_attack ), If an attacker is able to solve 15.8 million of the 180 million captchas, there will be a 50% probability that the attacker can beat the captcha. I tried refreshing the page 10 times, generating a total of 100 captchas. Out of those,…

Can you explain how the birthday paradox applies here?

Just looking at it simply, if you can solve 15.8 of 180, that means that for any given test you should have an 8.77% chance of solving it (6 tests for > 50%). What am I doing wrong?

Also, it looks like some of the other questions are easy to automate. Like "how many letters are in the word 'whatever'".

Re: TextCAPTCHA: 180 million simple logic questions

#49

Post by [deleted] »

GavinB wrote: post #33
patio11 wrote: post #29

I would be interested to see what the completion rate for this is versus, e.g., the Yahoo captcha. My intuition is "not that great." (You require reading on the Internet... uh oh.) By the way, picking one token from the captcha and returning it beats the captcha 7% of the time, if the examples are representative. Spammer wins, since he can generate requests by the hundreds of thousands.

Maybe the solution is to obscure the text somehow, so that a spammer can't read the text to grab a token . . . .

[deleted]

Re: TextCAPTCHA: 180 million simple logic questions

#50

Post by bmm6o »

Einh wrote: post #26
amih wrote: post #7

Some of the questions don't have one globally unique answer, for example: which day is a part of the weekend, Sunday, Friday or Monday. Where I live (Israel), Friday is part of the weekend, were as I bet the creator of the list lives in the USA and as many times happens, believes the USA==World and the "correct" answer is probably Sunday.

Stop bombing palestinian children and we'll start giving a fuck about what you call the weekend.

After lurking for 80 days, this is what you choose for your first comment?
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