# Captcha - HashCash - - Joomla! 3 - Joomla! 4 - Joomla! 5 - Joomla! 6 - [ plugin ](/content-tags/plugin) - [ captcha ](/content-tags/captcha) - [ Security ](/content-tags/security) ![Captcha - HashCash](https://cdn.richeyweb.com/images/articles/plg_captcha_hashcash/hashcash-16x9-meme2.webp) It's not another CAPTCHA you can't read, it's the CAPTCHA you don't even need to see. - [JED: Captcha - HashCash](https://extensions.joomla.org/extension/access-a-security/site-security/hashcash/) - [HashCash on Wikipedia](https://en.wikipedia.org/wiki/Hashcash) - [Inventor's Website](http://hashcash.org/) ## Stop Spam Without Annoying Your Users Frustrated visitors abandoning your forms because they can't read distorted CAPTCHA text? Tired of relying on Google's reCAPTCHA that tracks your users and raises privacy concerns? **Captcha - HashCash** is an invisible anti-spam solution that runs silently in the background - your users never see it, never interact with it, and never get frustrated. Your forms stay protected while your visitors enjoy a seamless experience. First Release: 2014 - three years before Google's invisible reCAPTCHA. No tracking. No data sent to 3rd parties. No Google. Overview--- ## Proven Protection for Modern Joomla Sites **"Superb - possibly the best Captcha available"** - John Vesey, March 2025 **"Easiest Solution for Blocking Spam/Bots"** - Greg Smela, March 2025 **"Smart, easy and efficient... Do exactly what it is supposed to do, and without annoying pictures to read or questions to answer"** - Philippe, October 2025 Listed in the [Joomla Extension Directory](https://extensions.joomla.org/extension/access-a-security/site-security/hashcash/) with 5-star reviews. Used by sites worldwide, mentioned on [Grokipedia's CAPTCHA page](https://grokipedia.com/page/CAPTCHA), and recommended by [VirtueMart](https://forum.virtuemart.net/index.php?topic=152320.0) and [CMS Junkie](https://www.cmsjunkie.com/forum/j-businessdirectory/captcha-error). [See it in action on our contact form →](/contact-us) ## How It Works When someone loads your form, their browser automatically solves a simple puzzle in the background while they're filling out the form. Real people never notice it happening - the calculation finishes before they click submit. But spam bots waste so much processing power trying to solve the puzzle that they give up or get blocked. No blurry images to decipher, no "select all the traffic lights" games, no Google tracking your visitors - just invisible protection that works. ## What You Get - **Invisible Protection** - Your users see nothing. No interaction required, just smooth form submission. - **Complete Privacy** - No external services, no Google tracking, no cookies. Fully GDPR and EU e-Privacy compliant. - **Works Everywhere** - Protects all Joomla forms automatically: contact forms, user registration, comments, everything. - **Zero Maintenance** - Install once, forget about it. No updates required, no API keys to manage, no subscriptions. - **Adjustable Security** - Choose your protection level from basic (fast) to maximum (stops even advanced bots). - **Background Processing** - Page stays responsive. The security calculation runs in a separate thread so nothing slows down. - **Bot Punishment Mode** - Optional feature that traps detected bots in impossible calculations, wasting their resources instead of yours. ## Frequently Asked Questions: Is this hard to install? Install like any Joomla plugin: download, upload through Extensions Manager, enable it in System > Plugins, and select it as your CAPTCHA method in Global Configuration. Most people finish in under 5 minutes. Will this slow down my site?No. The calculation happens in the user's browser while they fill out the form, using a background process that doesn't affect page responsiveness. Your server just verifies the answer—one quick check that takes milliseconds. What if I'm not technical?You don't need to be. The default settings work great for most sites. Just install and enable—it protects your forms immediately. Want to adjust the difficulty? Simple text field and radio button. That's it. Is it really free? Forever?Yes. No trials, no limits, no premium upgrades. Free to download, free to use, free forever. No registration required. Will this work with my forms?If it's a Joomla form, yes. Contact forms, registration, password resets, comments—it protects them all automatically once enabled. Third party forms? Maybe - if it uses the system-configured Captcha - then yes. What about privacy laws?HashCash is completely self-hosted. No data leaves your site, no external services, no tracking cookies. It's GDPR-compliant by design. ## Download Captcha - HashCash [ Captcha - HashCash 5.6.114354](/extension-repository/captcha-hashcash/plg_captcha_hashcash-5.6.1) [ Report a Bug](/bugs) [ Documentation](/software/documentation/captcha-hashcash) Technical Details--- ## Technical Specifications *For developers and the technically curious* ### Algorithm Options - **SHA-256** - Fast, basic protection (easily defeated by modern bots) - **SHA-384** - Medium protection - **SHA-512** - Strong protection - **PBKDF2** - Enhanced GPU resistance through memory-hard sequential hashing - **PBKDF2+64KB Memory Loop** - Maximum protection forcing 8-18 second solve times on GPUs while keeping user delays under 3 seconds [Detailed algorithm comparison →](/software/examples/hashcash/algorithm-options-explained-for-hashcash) ### Advanced Features - **Web Worker Implementation** - Hashing operations run in dedicated background thread ([technical details](/blog/development/hashcash-web-worker-revolution)) - **Delayed Calculation** - Waits for user interaction before starting calculation, blocking bots that submit too quickly or wait too long - **Configurable Difficulty** - Levels 1-5 adjusting hash complexity - **Optional Tor Blocking** - Prevent anonymous network abuse via Console - Tor Nodes integration - **Realtime DNSBL** - Multiple blacklist options for IP reputation checking - **Bot Punishment Mode** - Present unsolvable calculations to detected bots ### Technical Requirements - **Secure Context Required** - HTTPS on production (localhost acceptable for testing) - **JavaScript Enabled** - Uses Web Cryptography API and Subtle.Crypto - **Modern Browser** - Supports all current browsers with WebCrypto support - **PHP 7.2+** - Compatible with standard shared hosting - **Joomla 3.x, 4.x, 5.x, 6.x** - Native support, no backward compatibility layer needed for J5/J6 ### Standards & Implementation - Based on [HashCash proof-of-work concept](https://en.wikipedia.org/wiki/Hashcash) originally proposed by [Adam Back](https://en.wikipedia.org/wiki/Adam_Back) in 1997 - Implements memory-hard functions to resist GPU parallelization attacks - Sequential PBKDF2 with 10,000+ iterations forces several seconds per solve on GPUs - PBKDF2+64KB mode adds memory bandwidth bottleneck pushing GPU solve times to 8-18 seconds ### Security Notes - **CVE-2006-3750** does NOT apply to this extension - that vulnerability was in a different, unrelated Joomla extension from 2006 - Self-hosted solution eliminates third-party attack vectors - No cookies or external dependencies reduces privacy liability - Source available for security auditing ### Integration Notes If using **System - Page Cache** plugin, exclude form pages from cache by adding `com_users` and `com_contact` to the URL exclusion list in the Page Cache plugin's Advanced tab. ### About HashCash RicheyWeb did not invent HashCash - the concept was created by British cryptography expert Adam Back. We adapted this proven anti-spam technique into an accessible Joomla plugin. Learn more at [hashcash.org](http://hashcash.org/) or read the [Wikipedia article](https://en.wikipedia.org/wiki/Hashcash). Reviews--- ## 6 Reviews ### Retrieved from JED monthly #### Complete - Unfiltered ### HashCash is a helpful solution #### 2016-07-13 - Ali Functionality helpfulEase Of Use just enabling and selecting is enough ### Very Good Plugin #### 2019-08-26 - cyskye Functionality It really does the work and protects the contact form from spammers. Ease Of Use Very very easy: just download, install and enable the plugin. That's all. ### Superb - possibly the best Captcha available #### 2025-03-15 - John Vesey Functionality Packed with features and J5 native (no b/c plugin needed). Completely invisible save for an optional “spinner” whiles calculations done.Ease Of Use Really easy; just set in global configuration and set desired option via the plugin. Simple yes/no switches for the various options.Support Not needed, but Michael is active on the Forums and via direct contact. Like everything he does, it just works!Documentation Not used yet but will use to integrate functionality into non-standard forms. ### Easiest Solution for Blocking Spam/Bots #### 2025-03-20 - Greg Smela Functionality Great features including an optional spinner that lets people know it is working behind the scenes. Native for J5 so no b/c needed.Ease Of Use Extremely easy to set (and forget)! Instal the plugin and enable it. Optional switches can be set but generally not needed.Support Never needed support but the author is active on the forums and the documentation is comprehensive.Documentation See above. I've not needed docs for any of Michael's tools but know it is there if needed. ### Smart, easy and efficient #### 2025-10-25 - Philippe Functionality Do exactly what it is supposed to do, and without annoying pictures to read or questions to answer for the user.Ease Of Use Very simple. You install it, eventually change the very few preset parameters and that its.Support Support is not needed as hash-cash is so easy to install and to use. work immediately.Documentation No need for extensive documentation. What is avaialalbe on developper site is more than enough.#### Reply Thank you for the great review! ### Excellent solution #### 2026-01-31 - Hekate Functionality Very good for the more sofisticated bots, that can bypass other protection layers and register. This extension solves it.Ease Of Use Simple. Just configure it and select it as captcha at the user settings.Support Did not need any, the extension was easy to configure and worked without problems.Documentation Good one, at the developer's site, with explanation how it works.#### Reply Thanks for the great review! - [ email ](mailto:?subject=Captcha+-+HashCash&body=https%3A%2F%2Fwww.richeyweb.com%2Fsoftware%2Fjoomla%2Fplugins%2Fcaptcha-hashcash) - [ facebook ](https://www.facebook.com/sharer/sharer.php?u=https%3A%2F%2Fwww.richeyweb.com%2Fsoftware%2Fjoomla%2Fplugins%2Fcaptcha-hashcash) - [ x-twitter ](https://twitter.com/intent/tweet?text=Captcha+-+HashCash%3A+https%3A%2F%2Fwww.richeyweb.com%2Fsoftware%2Fjoomla%2Fplugins%2Fcaptcha-hashcash) - [ linkedin ](http://www.linkedin.com/shareArticle?mini=true&url=https%3A%2F%2Fwww.richeyweb.com%2Fsoftware%2Fjoomla%2Fplugins%2Fcaptcha-hashcash&title=Captcha+-+HashCash&summary=Stop+Spam+Without+Annoying+Your+Users+Frustrated+v...) - [ pinterest ](http://pinterest.com/pin/create/button/?url=https%3A%2F%2Fwww.richeyweb.com%2Fsoftware%2Fjoomla%2Fplugins%2Fcaptcha-hashcash&media=https%3A%2F%2Fcdn.joomla.org%2Fimages%2Fjoomla-org-og.jpg&description=Captcha+-+HashCash) [ Previous article: User - Static Email User - Static Email ](/software/joomla/plugins/user-staticemail) [ Next article: Content - Before/After Content - Before/After ](/software/joomla/plugins/content-beforeafter) ##### We Value Your Privacy We use cookies to enhance your experience and for traffic analysis. 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