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How robots and spiders are causing issues, how to stop them. We can also talk about Completely Automated Public Turing Test To Tell Computers And Humans Apart - their use, their compliance issues, porn proxies, PWNtcha and other ways to defeat them. 
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Sectioned circle Captcha
Posted by: The-Wildcat
Date: August 21, 2007 06:31AM

What about captchas like that: http://ent.the-wildcat.de/captcha/
Click the sectioned circle.

Are there any robots to solve this?

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Re: Sectioned circle Captcha
Posted by: Anonymous User
Date: August 21, 2007 06:47AM

Interesting idea, however if I click randomly -since the sectioned circle covers a great part- I'm able to pass the CAPTCHA fairly quick, couple of tries:

Random click result:
1,2,3,4 => success 
1,2,3,4,5,6,7,8,9,10,11 => success 
1,2 => success 
1,2,3,4 => success 
1,2,3,4 => succces 
etc...
Which would be brute forcable by sending the the mouse coordinates.

How about making the rings a lot smaller?
and put more of them into it to reduce bruteforcing the CAPTCHA?

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Re: Sectioned circle Captcha
Posted by: The-Wildcat
Date: August 21, 2007 06:55AM

Hm, thats bad.

Here, a little smaller and a lot more circles

http://ent.the-wildcat.de/captcha/index2.php

Edit:

To protect against bruteforcing by sending mouse coordinates, you can also add
a form key



Edited 1 time(s). Last edit at 08/21/2007 07:26AM by The-Wildcat.

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Re: Sectioned circle Captcha
Posted by: Super-Friez
Date: August 21, 2007 10:31AM

I can see where this could be used, but I think the only problem is that users with bad eye sight will have a hard time!

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Re: Sectioned circle Captcha
Posted by: The-Wildcat
Date: August 21, 2007 10:37AM

Hm, this captcha isn't good for accessibility, thats true.
But, you can implement "accessibility" by readjusting size of the circles.



Edited 3 time(s). Last edit at 08/21/2007 10:42AM by The-Wildcat.

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Re: Sectioned circle Captcha
Posted by: rsnake
Date: August 21, 2007 11:45AM

I think this would be a pretty easy one to solve programmatically. Both by simply clicking a bunch of times in the same spot, (the spot is actually much smaller than the size of the box, because the circles don't go outside of the boundary of the box (nor could they without making it impossible to tell which one is broken). Simply by centering my mouse I'm getting pretty decent rates of success (one out of 6 for the first one).

But further I think this would be fairly easy to solve by computing the arcs of each circle (which is pretty easy, since it's a circle) and seeing where you see a significant drop-off of color. Assuming it isn't in collision with another circle which also causes that a computational difference in color you have your answer. I bet a good programmer could solve it in under a day.

But my last problem with this is that it's very very hard to solve for humans in certain cases. That makes it a failed CAPTCHA. It's supposed to be easy for humans and hard for robots. This is almost the opposite in some of the example images I've seen.

- RSnake
Gotta love it. http://ha.ckers.org

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Re: Sectioned circle Captcha
Posted by: The-Wildcat
Date: August 21, 2007 01:31PM

another alternative would be: click the intercept point of the two white circles (or any other specified color)
Is this also easy to solve?

http://ent.the-wildcat.de/captcha/alternative.php

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Re: Sectioned circle Captcha
Posted by: FiSh
Date: August 21, 2007 01:40PM

I like the idea, but the area in the first two is large enough that after 3 or 4 tries you will get a success by just random clicking, and the last one may be frustrating to users with bad eyesight.



Edited 1 time(s). Last edit at 08/21/2007 01:41PM by FiSh.

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Re: Sectioned circle Captcha
Posted by: kuza55
Date: August 21, 2007 10:06PM

The-Wildcat Wrote:
-------------------------------------------------------
> another alternative would be: click the intercept
> point of the two white circles (or any other
> specified color)
> Is this also easy to solve?
>
> http://ent.the-wildcat.de/captcha/alternative.php


Yeah, that's even easier to solve, the hardest thing for a computer would be correlating a written colour "white" to the actual rgb representation of the colour (FFFFFF), which could be fairly easily done by a simple lookup table.

Furthermore, once this is done, there are only 3 possibilities, inside 1 circle, inside the intersection, and inside the second circle, and even 33% is a high hit rate.

And even then it would be easy to determine which non-white part is the intersection part, simple by determining which of the 3 sections is in the middle.

You could make ti harder by adding more white circles which don't intersection, but it should still be fairly easy to solve, simply by determining which white outlines are single circles, rather than intersected circles.

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Re: Sectioned circle Captcha
Posted by: istari
Date: August 22, 2007 11:09AM

Hmmm, I really don't see this kind of CAPTCHA going anywhere, as circles are too easy to identify programatically, and more so if they all have the same, fixed radius...
I've solved stuff like this in just a few hours, not for CPATCHA processing but for algorithm programming competitions. Basically, one makes a grid (or samples random pixels) and then uses a convex hull algorithm [en.wikipedia.org] to find the shapes formed by the pixels that are of the same colour. You can determine with almost absolute certainty where two shapes intersect, or which circle is sectioned (by sampling enough pixels on each circle's border)...

All in all, I'm pretty sure one would be able to get pretty good results in little time, and great results if some effort is thrown in (and I'm talking about 90% ratios here!)...

If you designed these CAPTCHAS, then try varying circle radius, and having a non-uniform background. That would complicate things quite a bit, but then again, it might be too much even for humans!



Edited 1 time(s). Last edit at 08/22/2007 11:10AM by istari.

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Re: Sectioned circle Captcha
Posted by: FiSh
Date: August 22, 2007 12:02PM

What about a captcha with stock photos, where you have to identify two of the same object from different photos? Any human should be able to do it, but it might be a little more difficult for a robot to figure out. You'd have to have a lot of stock photos though..

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Re: Sectioned circle Captcha
Posted by: nEUrOO
Date: August 30, 2007 08:01AM

As RSnake said, it's really easy to detect the circles and the sectioned circles with image recognition... (laplacian filter + trying to fit circles)
Well, old classes rest :)

nEUrOO -- http://rgaucher.info -- http://twitter.com/rgaucher

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Re: Sectioned circle Captcha
Posted by: Anonymous User
Date: August 31, 2007 04:26AM

Time to file this one also in the Museum of unworkable devices, along with the other perpetual motion devices, CAPTCHA's are dead, they don't work. ^^

http://www.lhup.edu/~dsimanek/museum/unwork.htm

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Re: Sectioned circle Captcha
Posted by: Spyware
Date: August 31, 2007 05:16AM

It did "work".

He is wise who gains wisdom from another's mishaps.

—Plutius Syrus

The CAPTCHA's failed but because of their failure we have gained knowledge. So it did do something. They weren't useless.

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Re: Sectioned circle Captcha
Posted by: Anonymous User
Date: August 31, 2007 06:43AM

Yeah it means we should quit persuiting it, since it will never work.

If someone can solve the (inverted) turing test he basically also solves the (P=NP) problem partially. Which would be the biggest discovery ever, since the (P=NP) problem takes an infinite amount of time to solve, and therefore likely never will be solved. => http://en.wikipedia.org/wiki/P%3DNP_problem

For clarity, I had to add, that a CAPTCHA isn't really a turing test but more an inverted one.



Edited 2 time(s). Last edit at 08/31/2007 06:52AM by Ronald.

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Re: Sectioned circle Captcha
Posted by: nEUrOO
Date: August 31, 2007 08:59AM

Ronald: I really think that CAPTCHA are weak, and this because of what you said. But we have to admit that a CAPTCHA is a correct way to reduce the number of automated stuff, but this is only a short time protection... This is pretty much the same thing everywhere, one side (white) is learning from the other and vice versa.

So, I don't think we should stop using of CAPTCHA, but researchers also have to think on other solution to stop automated programs.

nEUrOO -- http://rgaucher.info -- http://twitter.com/rgaucher

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Re: Sectioned circle Captcha
Posted by: Anonymous User
Date: August 31, 2007 09:06AM

Yeah, I thought like that for a long time, but I realized that it's useless to have something that fails to protect, afterall you use it to stop it, and that does not work because all CAPTCHAs more or less fail, so it is only annoying.

I was realy convinced by the `CAPTCHA breaking game` we saw a few months ago, where a site showed Google captchas and promised users prizes when they could "crack" 10 or more captcha's. Even blogspot captcha's are already broken.

It's flawed, and it doesn't work, and therefore it is just useless to have one.

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Re: Sectioned circle Captcha
Posted by: Anonymous User
Date: August 31, 2007 09:08AM

I rather suggest to throttle the number of tries but that involves huge amounts of code to perform correctly. And that isn't something you just upload to a server, further than that CAPTCHA's fail to do what they promise.

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