Re:I broke textCAPTCHA with Python
by Xk on Friday November 12, 2010 @11:02AM
(#1898050)
Yeah, but I have the advantage of knowing all the forms of the questions. If you were to change one word then mine would break. Or misspell anything.
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Re:I broke textCAPTCHA with Python
by techiferous on Friday November 12, 2010 @12:02PM
(#1898277)
I just typed in similar questions without following the format and it performed poorly. But at least it's a good proof-of-concept! :)
Name the third item in the list: book, fork and spoon.
A: FAILURE
Q: What is two times 8?
A:
Which is a number: yellow, seven, book, flag?
A: FAILURE
They don't give questions formatted in other ways, so I didn't include that in the logic. As someone else pointed out, even deleting the question mark would break it. (However, making the question mark optional would be a two second fix.)
Sorry, but what do you mean by "knowing all the forms of the questions"? It seems like maybe you mean all that all the questions formatted via one of several formulas like: name <x> of list<a..z>. Which would imply your tool simply identifies the format then applies some specific logic to solve the question. I'm unclear that if that is what you mean, why then do you know all the forms of the questions? Text capture purports over 180 million questions, so isn't it likely you may not have found all the possible formats of the questions? Or perhaps did you know because you have a relationship with the text captcha creator and they provided that info to you. Or better yet, did your comment mean something entirely different.
Just curious, thanks.
You are correct, I look for a pattern and apply very very basic logic.
I just got 1,000 questions from the demo page and looked how they were similar. For example, there are many questions of the form "[list of something]: the [ordinal number] [type] is?" so I put that as a rule in the grammar file. I did this for about twenty different types of questions, each of which has three or so different phrasings.
And yes, they may have 180 million questions, but in reality they have only a hundred or so modulo the specific words they pick (for the items in the list, or for the day of the week, or for the letter that the word starts with).
> I put that as a rule in the grammar file
I wrote a parser generator, so I'm using that.
It's BNF-like.
It's basically an arms race. They could inject a few misspellings and random noise here and there to throw your system off.
Fuzzy pattern matching would probably solve that.
Great job! I wrote up that post about WolframAlpha and wonder if there's an API so you could integrate WA to make it more robust?
Right now there's no API or anything -- I wrote this just to see if I could. I'm not sure if I'll be putting up an API, because I figure by the time I'd do that I can just release the source for it. But if you really wanted I probably could provide an API it in a couple of days.