Month: January 2004

In response to this

I like the second of the two, since it’s not exclusionary. How hard would it be to defeat? And what countermeasures could be written into it (present the string as HTML entities that have to be decoded by a parser? present the word reversed? don’t use real words at all? make the letter position the result of a simple equation [what letter is in the 2^2 position in the string uiwplkg?]?)

a friend writes:

None of those countermeasures would be effective against a computer parser; most of that stuff doesn’t even matter to a computer, like whether it’s a real word or if there’s an expression to evaluate. That’s all stuff that a computer is really good at.

On the other hand, you could describe the operation to be performed in such a way that it’s hard to get the gist without fully grokking the English:

“In an attempt to verify that you are a living, breathing human being and not a mindless computer program, and not having the time or resources to arrange a Turing Test, we would like you to enter, in the blank below, the answer indicated by the following paragraph.

The previous paragraph contains words of several parts of speech: prepositions, articles, nouns, verbs, pronouns, adjectives. Locate the first word which belongs in that last category and enter the letter which appears in it twice.

Enter answer here:[ ]”

Of course, that’s a bad example because it exclude people who were ignorant of the intricacies of English parts of speech (when is a verb form an adjective?). But it’s the right kind of example, I feel. The idea is to make the statement of the problem as hard to parse as possible. Avoid using digits; spell out numbers and require them to be spelled out. Pull together various parts of the text with references that are unambiguous but not computationally precise. That sort of thing. And of course, there has to be a very, very large set of potential problems and answers so that it doesn’t boil down to capturing all of the questions and memorizing the correct responses with no grokkage required at all.

So randomness (to create a large problem set) and high degree of difficulty in parsing, in effect negating simple parsing, are the specifications.

[Posted with ecto]

Plastic: I Don’t Need To Buy Your CDs Anymore . . . . :

“Every Mac is now a potential recording studio. This stuff is great for people learning an instrument and terrible for people making money off kids trying to put together a demo in an overpriced studio”

[Posted with ecto]

There’s a lot of effort going into how to prevent comment spam in movabletype and other weblogs. The key seems to be finding something that approximates a crude Turing test: the post request must meet some challenge that only a human can meet.

There are a few coping strategies in the field. One is a “captcha” engine that creates a gif of a number string and requires the numbers to be keyed as a kind of authentication: the gif is somewhat obscured, making it a problem for the sight-impaired and, we suppose, OCR software.

Another idea, not yet fielded, is a challenge-response where the question is something like “what is the X letter of word Y”? The arguments against this seem to be that a parser could be written to sort that out . . . I suppose so.

I like the second of the two, since it’s not exclusionary. How hard would it be to defeat? And what countermeasures could be written into it (present the string as HTML entities that have to be decoded by a parser? present the word reversed? don’t use real words at all? make the letter position the result of a simple equation [what letter is in the 2^2 position in the string uiwplkg?]?)

With the understanding that no scheme is perfect, what makes the bar sufficiently high as to dissuade all but the morally bankrupt with a lot of time on their hands?

[Posted with ecto]