mCaptcha

Proof of work based, privacy respecting CAPTCHA system with a kickass UX.

STATUS: ACTIVE DEVELOPMENT

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mCaptcha is a privacy respecting, free CAPTCHA system with a kickass UX. Your users no longer have to interact with ridiculous image-based CAPTCHA system, wasting precious mental bandwidth. Instead, your computer will do the work for you, see for yourself!

How does it work?

mCaptcha uses SHA256 based proof-of-work (PoW) to rate limit users.

When a user wants to do something on a mCaptcha-protected website,

1. they will have to generate proof-of-work (a bunch of math that will takes time to compute) and submit it to mCaptcha.

2. We'll validate the proof:

   • if validation is unsuccessful, they will be prevented from accessing their target website
   • if validation is successful, read on,

3. They will be issued a token that they should submit along with their request/form submission to the target website.

4. The target website should validate the user-submitted token with mCaptcha before processing the user's request.

The whole process is automated from the user's POV. All they have to do is click on a button to initiate the process.

mCaptcha makes interacting with websites (computationally) expensive for the user. A well-behaving user will experience a slight delay (no delay when under moderate load to 2s when under attack; PoW difficulty is variable) but if someone wants to hammer your site, they will have to do more work to send requests than your server will have to do to respond to their request.

Why use mCaptcha?

• Free software, privacy focused
• Seamless UX - No more annoying CAPTCHAs!
• No tracking: Our CAPTCHA routes are cookie free!
• IP address independent: your users are behind a NAT? We got you covered!
• Resistant to replay attacks: proof-of-work configurations have short lifetimes (30s) and can be used only once. If a user submits a PoW to an already used configuration or an expired one, their proof will be rejected.

Demo

Client-side widget:

mCaptcha's UX is super silent, solving CAPTCHAs have never been more easier. One click and you are on your way. To observe mCaptcha in action, open dev tools and monitor console and network activity.

1. Link to widget

2. Video:

Demo servers are available at:

• https://demo.mcaptcha.org/
• https://demo2.mcaptcha.org/ (runs on a Raspberry Pi!)

Core functionality is working but it's still very much work-in-progress. Since we don't have a stable release yet, hosted demo servers might be a few versions behind master. Please check footer for build commit.

Feel free to provide bogus information while signing up (project under development, database frequently wiped).

Self-hosted:

Clone the repo and run the following from the root of the repo:

git clone https://github.com/mCaptcha/mCaptcha.git
docker-compose up -d

After the containers are up, visit http://localhost:7000 and login with the default credentials:

• username: aaronsw
• password: password

It takes a while to build the image so please be patient :)

See DEPLOYMENT.md for detailed alternate deployment methods.

Development:

See HACKING.md

Deployment:

See DEPLOYMENT.md

Configuration:

See CONFIGURATION.md

Funding

NLnet

2023 development is funded through the NGI0 Entrust Fund, via NLnet. Please see here for more details.