Re: RFC: CGI::Application::Plugin::CAPTCHA

Tony Fraser wrote:
> On Fri, 2005-08-26 at 14:35, Michael Peters wrote:
> > Ok, before we go down this road, can anyone give me a good reason that
> > we need to permanently store these images or even cache them? The
> > CAPTCHA phrase should be random enough that we would never use the same
> > image twice in a reasonable amount of time right?


Time to add my two cents:

1) since the whole business is about preventing spamming, saving images 
on disk is actually a BAD idea: if a robot hits your script repeatedly, 
you'd end up with tons of uselessly generated images, which waste both 
processing power and disk space.

2) Since these images get used once, and only once, it makes perfect 
sense to only generate them when they're really needed.

I think that puts me firmly in Michaels camp :)

> To me that leaves 2 choices:
>
> 1. Store the plain text on the server somehow, indexed by the hash. Then
> generate the image as needed.
>
> 2. Generate the image and the hash at the same time and somehow save the
> image so that it can be retrieved by its hash in a separate HTTP
> request.


The plaintext string would be what, 8 bytes? How big would the image be, 
3Kb? Easy choice there.


> If you put the info required to generate the image in the query string
> of the runmode that generates the image you've just given the robots
> everything they need to defeat the captcha.


Depends on the form in which you pass that information. If you use a 
decent two-way encryption, there's no harm in my opinion. That way you 
don't even have to store anything on the server: pass the encrypted text 
both in the form (hidden) and in the captcha_create url. When you get 
the form data, see if encrypted and plaintext match. Simple and clean.

Rhesa



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