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Everyone knows the annoyance caused by captchas that are unreadable. HashCash is a different kind of validation. Unlike other captcha solutions, HashCash doesn't rely on 3rd party services or resources - and it doesn't require anything from your users other than a JavaScript enabled browser. No mangled words to decipher, no math problems to solve, no photos to match - nothing but arrival on a form page.

Originally proposed by Adam Beck in 1997, HashCash requires a form to include the solution to a complex calculation. The calculation is so complex (it takes hundreds or even thousands of attempts to solve it) that any human or bot attempting to abuse your forms will spend so much processor time solving the calculation that it wouldn't be profitable to continue attacking your forms! The server receives the result and can easily and quickly test the answer in 1 calculation - either it's right and your user continues or it's wrong and the form submission fails.

The best part is, HashCash is invisible (you can't read it - or even see it) and it happens in the background without user interaction! Your users arrive at the form and the HashCash calculation is automatically executed. Any bot attempting to submit your form without completing the calculation is rejected, and the calculation changes every time the form is submitted.

Configuration is simple. Open the plugin and choose the difficulty level. The predefined minimum (1) and maximum (4) levels prevent calculations that are too simple or too difficult to complete in an acceptable amount of time.


  • Configurable difficulty level
  • No mangled text that nobody can read
  • Completion happens automatically, without user intervention
  • Nothing to annoy your users

Download HashCash 1.6.6

Bug Reports

Documentation: Online

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Paid Extension FAQ

What am I buying?
  • The extension
  • One year of updates
  • Support
Do you still support free versions?
Only bugfixes
Can I install the extension on multiple sites?
Go for it
Can I give a copy to my friend?
While this is ethically wrong, there is no easy way for me to stop it. However, if your friend wants support he should call you - because I won't talk to him unless he purchases the extension.
What happens to the extension at the end of the year?
Nothing. It remains installed and configured, it just stops receiving updates and support is suspended.
What if I give you an idea that you turn into a paid extension?
You'll be given a lifetime subscription for that extension.
What if I contract you to make a custom extension for me?
There are two options, and I may or may not offer both.
  1. You will be given a quote for outright ownership of the extension.
  2. If it's something that I believe will benefit the community, I may offer a reduced quote where I retain ownership along with the promise that it will remain a free extension.