# Captcha - HashCash Documentation - Extension Page: [Captcha - HashCash](/software/joomla/plugins/captcha-hashcash) ## Overview Finally, a CAPTCHA you can’t read—because you don’t need to! [Captcha - HashCash](/software/joomla/plugins/captcha-hashcash) is the CAPTCHA that works behind the scenes, invisible to users and relentless against bots. Say goodbye to the frustration of squinting at distorted text or matching blurry photos. HashCash takes a different approach: it’s a client-side validation plugin for Joomla that doesn’t rely on third-party services, external resources, or user effort beyond a JavaScript-enabled browser. No mangled words, no math puzzles, no photo grids—just seamless form protection that kicks in the moment a user lands on your page. First proposed by Adam Back in 1997, HashCash uses a proof-of-work system where the client must solve a complex SHA-256 hash calculation. At its default difficulty (level: 3), this takes hundreds or thousands of attempts, taxing any bot or human abuser enough to make spamming unprofitable. The server verifies the result in a single, lightning-fast check—correct, and the form proceeds; incorrect, and it’s rejected. For detected bots, the optional punish mode cranks the difficulty to an unsolvable level: 32, effectively locking them out. HashCash runs invisibly in the background, triggered automatically on form load or user interaction (configurable via Delay Start). It combines this computation with a nine-check gauntlet to sniff out bots—everything from fake events to headless browser signatures. An optional nonce trap adds another layer, catching stealth bots that tamper with a hidden field. The result? Your users experience nothing but a smooth form, while bots hit a computational wall. ## Installation 1. Download HashCash: Grab the latest version from the RicheyWeb download page. This link may shift over time, so head to http://www.richeyweb.com and search for "HashCash" to find it. 2. Navigate to Joomla Admin: In your Joomla /administrator, go to Extensions > Manage > Install. 3. Upload the File: Select the Upload Package File tab, click Choose File to locate the downloaded plugin, and hit Upload & Install. 4. Enable the Plugin: The extension is now installed but disabled. Go to Extensions > Plugins, search for "HashCash," and open it to configure and enable. ## Configuration Configuring HashCash is straightforward—open the plugin in the Joomla Plugin Manager and tweak these options: 1. Hash Algorithm: - Sets the computational method for generating the hash. - SHA-256: Basic Protection - SHA-384: Standard Defense - SHA-512: Advanced Bot Blocking - PBKDF2: GPU-Resistant - PBKDF2+64KB: Maximum Deterrence 2. Difficulty Level: - Sets the number of leading zeros required in the hash (default: 3). Options range from 1 (easiest) to 4 (hardest), balancing bot deterrence with quick computation times—typically milliseconds at level 3. - Recommended level 3. This balances speed with security. It's not too easy that there's no computational cost, and it's not so hard that it takes more than a few seconds to run. On a 4-core (8-thread) 2.8GHz Xeon E3-1505M it takes between 5 and 30 seconds to solve a level 4 hash. Higher difficulty levels lead to longer waits. - Default level 3. 3. Delayed Start: - When enabled, the HashCash calculation does not begin until the user interacts with the form. They must type something, click a radio button or checkbox, select something from a select list - whatever it is, they must interact before the calculation begins. - This enables all other advanced functionality below. 4. Decorate Known Forms: - Known forms are modified on page load to disable the submit button and replace its text with a BS5 spinner and "Loading..." text. Upon successful calculation, the button is returned to its original state. - Find instructions to decorate other forms below. Let me know if you'd like your decorator added to the plugin. - Supported Forms: - com\_contact.contact (Joomla Contact Form) - com\_users.registration (Joomla User Registration Form) - com\_users.remind (Joomla Username Reminder Form) - com\_users.reset (Joomla Password Reset Form) 5. Enable CDP Runtime Test: - Headless bots may be using the Chrome DevTools Protocol (CDP), which can be detected if no countermeasures are used. - This is disabled by default, because some developers may have this extension running on their developers. It's an edge case that can cause false-positives in the bot detection. This bot detection is logged in the JavaScript console if caught by the plugin. - Disabled by default. 6. Enable Nonce Test: - Bots that are not specifically programmed to ignore this field might be caught manipulating it. - Safe to enable, disabled by default. 7. Trigger JS Event: - Users who want to track bot detection can enable this, and implement some method to collect the data. - Example Google Analytics tracking is detailed in the article [Tracking Spam Bots Like a Pro with GA and HashCash](/software/examples/hashcash/tracking-spam-bots-like-a-pro-with-ga-and-hashcash) 8. Punish Bots: - Bots who are identified by the plugin can be forced to initiate an impossible hashing task. - Enabling this is recommended. - Disabled by default 9. Enable TOR Detection: - Requires [Console - Tor Nodes](/software/joomla/plugins/console-tor-nodes) - When enabled, visitors attempting to access your form through a Tor node are denied. They can fill out the form (waste their time) but the server will never accept it. 10. Enable DNSBL Check: - Visitors who are known spammers are rejected. 3 DNS blacklists to choose from. Policy blacklists (a Spamhaus designation) are not triggered - only reputation blacklists. ## Using HashCash With Joomla Caching When/if you have enabled Joomla caching in Global Configuration, you may notice that Captcha - HashCash fails intermittently. This is because the source of the hash (IP address and timestamp) are cached by Joomla until the cache expires or until the page is re-cached as the result of a POST. If you experience this, the solution is quite simple. Install my [System - Expires Headers](/software/joomla/plugins/system-expires-headers) plugin and create a menu item configuration. Within that configuration, set the menu item as below - specifically activating Disable Joomla Caching checkbox. ![Dealing with Joomla Cache](https://cdn.richeyweb.com/images/articles/plg_captcha_hashcash/expires-headers-caching.webp) ## Decorate Your Form To decorate your form, you will need to know the form context (the option and the view), for example option=com\_contact&view=contact and create a javascript file. When correctly named (option.view.js and option.view.min.js) is present in /media/plg\_captcha\_hashcash/js - the plugin will automatically load it when in that form context. See /media/plg\_captcha\_hashcash/js/com\_contact.contact.js for an example. ### Basic JavaScript structure: ``` const plg_captcha_hashcash_option_view_class = function() {

    const root = this;

    const construct = function() {

// do stuff to decorate the form

    window.addEventListener('plg_captcha_hashcash_finished', () => {

      // do stuff to un-decorate the form

  });

    }

    construct();

}

window.addEventListener('DOMContentLoaded', () => {

  new plg_captcha_hashcash_option_view_class();

}); ``` ## Error Messages To prevent giving attackers too much information, there is only one error message this plugin will display: Security validation failed. You may have waited too long to submit the form. The plugin may block based on many factors, bot browser detected - TOR node, DNS Blacklist. 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