Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Using WolframAlpha to Hack Text CAPTCHA

joelvanhorn.com

Post reply on HN
Print view View original

31–40 of 47 posts

Re: Using WolframAlpha to Hack Text CAPTCHA

#31

Post by gridspy »

phwd wrote: post #30

I am not sure I understand what he is saying. All the "results" that he is talking about are the interpreted inputs for the application to process. So for," What is seven hundred and forty four as a number? ", the interpreted input is a NumberQ function taking the main part "seven hundred and forty four as a number" and evaluating whether it is a number or not. The real result is true. The zoologist one has already b…

Even a 1/10 hit rate is sufficient. You get 10 questions from the website, return the results and one of them leads to your spam comment being posted. You then repeat that process thousands of times.

Re: Using WolframAlpha to Hack Text CAPTCHA

#33

Post by moshezadka »

elliottcarlson wrote: post #15
joelvh wrote: post #13

Earlier quoted context omitted.

If you were able to analyze the sentence structure of all 180 million questions, how many different sentence structures would there be? This all points to the fact that you can build algorithms to guess the answers eventually.

Not even just guess them but accurately determine them. A few years back I was hired by a third party to build a system to break the CAPTCHA on a popular site for various evil deeds. Morals set aside, the money was good and I had a wedding to pay for. A CAPTCHA system becomes quite breakable when it becomes predictable. The system in question used an image based CAPTCHA that used the same (albeit annoying) font for e…

It can't work the way you explained it: I just solved your CAPTCHA with 33% success rate (waaay too high for a useful CAPTCHA). Perhaps if you ask for "the three pictures of X animal out of those 9", and you had a database with which animal has which property (and you also ran some fuzz over the images so no two images would ever be the same). I'm still skeptical...

Re: Using WolframAlpha to Hack Text CAPTCHA

#34

Post by jerf »

elliottcarlson wrote: post #22
gojomo wrote: post #20

Some ALMOSTs could be turned into SUCCESSes with a few postprocessing rules-of-thumb, like: - the CAPTCHA usually wants a single word or number - the desired word is usually the rarer or later one

It's still a game of guesswork. Generally if you fail the CAPTCHA you will be offered a new one; and any good system should lock you out after a certain amount of failures.

Assume spammers are using botnets. The problem of locking them out is as hard as detecting them in the first place.

Re: Using WolframAlpha to Hack Text CAPTCHA

#35

Post by liuliu »

The idea: randomly pick one word in the input and make it to be the answer. It seems from the demo page that most of the answers is already in the question. Suppose 50% of questions that have answers in them, and suppose the average length of the question is about 10 words, you have 5% chances to get it right. and with a computer, this is a quite easy one.

Re: Using WolframAlpha to Hack Text CAPTCHA

#36

Post by elliottcarlson »

moshezadka wrote: post #33
elliottcarlson wrote: post #15

Earlier quoted context omitted.

Not even just guess them but accurately determine them. A few years back I was hired by a third party to build a system to break the CAPTCHA on a popular site for various evil deeds. Morals set aside, the money was good and I had a wedding to pay for. A CAPTCHA system becomes quite breakable when it becomes predictable. The system in question used an image based CAPTCHA that used the same (albeit annoying) font for e…

It can't work the way you explained it: I just solved your CAPTCHA with 33% success rate (waaay too high for a useful CAPTCHA). Perhaps if you ask for "the three pictures of X animal out of those 9", and you had a database with which animal has which property (and you also ran some fuzz over the images so no two images would ever be the same). I'm still skeptical...

That would assume that it is multiple choice - however if it's still free form text input, requiring the input to equal "frog" would solve that issue. Text + images + logic would offer a lot more hurdles than just any single one of those.

Re: Using WolframAlpha to Hack Text CAPTCHA

#38

Post by joelvh »

elliottcarlson wrote: post #15
joelvh wrote: post #13

Earlier quoted context omitted.

If you were able to analyze the sentence structure of all 180 million questions, how many different sentence structures would there be? This all points to the fact that you can build algorithms to guess the answers eventually.

Not even just guess them but accurately determine them. A few years back I was hired by a third party to build a system to break the CAPTCHA on a popular site for various evil deeds. Morals set aside, the money was good and I had a wedding to pay for. A CAPTCHA system becomes quite breakable when it becomes predictable. The system in question used an image based CAPTCHA that used the same (albeit annoying) font for e…

Interestingly enough, WolframAlpha can generate a CAPTCHA image of each of these text questions, as to make it harder for a bot to decode AND answer the question! Check it out: http://www.wolframalpha.com/input/?i=CAPTCHA+What+is+seven+h...

Re: Using WolframAlpha to Hack Text CAPTCHA

#39

Post by codefisher »

At the end of the day this is why I don't use CAPTCHA's on my site, they can be broken by a bot that is smart enough. The better option is to use something to analyse the contents of the spam to decide what it really is, and there are some tools that are really good at doing this. Heck I even found for one form that banning 'http:// (and notifying users with JavaScript if they typed it) stopped 100% of the spam I was getting.

Re: Using WolframAlpha to Hack Text CAPTCHA

#40

Post by ahlatimer »

mquander wrote: post #11
pygy_ wrote: post #7

Earlier quoted context omitted.

> "2nd fruit in bear apple goat orange"[1], "7th digit in abc123def456ghi789"[2] It barfs on these ones, but not like you predict (it's actually worse). "The 2nd colour in purple, belly, yellow, arm, white and blue"[3] gives back yellow, though, so it's not that stupid. [1] http://www.wolframalpha.com/input/?i=The+2nd+fruit+in+bear+a... [2] http://www.wolframalpha.com/input/?i=7th+digit+in+abc123def4... [3] http://ww…

Oh, not that stupid, huh? Query: The 2nd colour in purple, belly, yellow, arm, white and blue Answer: yellow Query: The 3rd colour in purple, belly, yellow, arm, white and blue Answer: yellow Query: The 7th colour in purple, belly, yellow, arm, white and blue Answer: yellow Query: The bluest colour in purple, belly, yellow, arm, white and blue Answer: yellow :-)

If you change yellow to silver, it gives you "colour silver," but if you look at the assumptions, it assumes silver is an element. Clearly it's not really getting the meaning of the sentence, and the fact that it's picking "yellow" is mostly coincidental, I think, as is also illustrated by your examples.

http://www.wolframalpha.com/input/?i=The+2nd+colour+in+blue,...

Post reply on HN