I know some people that would fail a few of these questions...
One could make a case for deliberately weeding such people out of whatever system the CAPTCHA is intended to protect.
TextCAPTCHA: 180 million simple logic questions
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Re: TextCAPTCHA: 180 million simple logic questions
#32Trying all the words in the captcha one by one has a big chance of "hitting" correct answer. If it doesn't a brute-forcer can just request a new captcha until it works. Said that, they don't seem very spam-proof to me. For more info about how hard CAPTCHAs need to be read Luis Von Ahn's papers: http://www.cs.cmu.edu/~biglou/
I get the impression that about half of the questions are list based. And the questions are about 10 words long. If that's the case, then using the algorithm you mentioned, you have a 1 in 20 chance of getting the captcha right. So yeah, it's a completely useless captcha system. That number should be 1 in a million or higher, not 1 in 20.
And it's probably not the first or last word. And if it precedes a ',' then it's probably more likely to be it. There are many ways to increase the hit-rate.
Re: TextCAPTCHA: 180 million simple logic questions
#33I 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 . . . .
Re: TextCAPTCHA: 180 million simple logic questions
#34Earlier quoted context omitted.
I get the impression that about half of the questions are list based. And the questions are about 10 words long. If that's the case, then using the algorithm you mentioned, you have a 1 in 20 chance of getting the captcha right. So yeah, it's a completely useless captcha system. That number should be 1 in a million or higher, not 1 in 20.
And it's probably not the first or last word. And if it precedes a ',' then it's probably more likely to be it. There are many ways to increase the hit-rate.
Sure. I know my calculation was very rough, but my point is, if I'm not at least 2 orders of magnitude out, then the captcha system is very very bad.
Re: TextCAPTCHA: 180 million simple logic questions
#35Some 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.
He's UK-based according to his personal pages.
Re: TextCAPTCHA: 180 million simple logic questions
#36"Ten, 33, thirty five, 10 and thirty six: the 5th number is?" 10? Thirty? Thirty Six?
Your point is that this captcha system may prevent smart-alec pedants from commenting? Man, that's a feature not a bug.
Re: TextCAPTCHA: 180 million simple logic questions
#37I 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.
I also noticed that certain questions aren't necessarily 'easy'.
> The 1st number from 25, eight, 6, six and 27 is?
So is the answer 25 or 6?
I've come to the realization that CAPTCHAs aren't the solution, or at least can't be a standalone solution. Make the CAPTCHA easy enough for a human to not be blocked (pick the cat from these 3 photos) and the bot still wins 33% of the time. Make it hard enough that the user has to invest energy to 'solve' the problem in front of them and you alienate users by treating them like criminals.
Re: TextCAPTCHA: 180 million simple logic questions
#38180 million isn't all that many. Keeping the answers in a database is trivial. Extracting the answers by trial and error is feasible. You'll probably want a large botnet to avoid getting blocked for suspiciously high traffic. If the servers can take an extra kqps or so, you should be done in about a week.
Re: TextCAPTCHA: 180 million simple logic questions
#39I 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.
I also noticed that certain questions aren't necessarily 'easy'. > The 1st number from 25, eight, 6, six and 27 is? So is the answer 25 or 6? I've come to the realization that CAPTCHAs aren't the solution, or at least can't be a standalone solution. Make the CAPTCHA easy enough for a human to not be blocked (pick the cat from these 3 photos) and the bot still wins 33% of the time. Make it hard enough that the user ha…
I don't get how the answer could be 6, though I do agree with you on the paradox of CAPTCHAs
Re: TextCAPTCHA: 180 million simple logic questions
#40Earlier quoted context omitted.
I also noticed that certain questions aren't necessarily 'easy'. > The 1st number from 25, eight, 6, six and 27 is? So is the answer 25 or 6? I've come to the realization that CAPTCHAs aren't the solution, or at least can't be a standalone solution. Make the CAPTCHA easy enough for a human to not be blocked (pick the cat from these 3 photos) and the bot still wins 33% of the time. Make it hard enough that the user ha…
I don't get how the answer could be 6, though I do agree with you on the paradox of CAPTCHAs
Interpretation 1: It's a string list and pick the first element = 25.
Interpretation 2: It's a numerical list of numbers, numbers being ordered by value have an implicit sort applied to them, pick the first element in that sequence = 6.
#2 is a very programmer thing to do ;)