HeCAPTe
Humane, embeddable Cost-Asymmetric Proof-of-work Turing exam

Hello! I was looking for a particular kind of self-hosted service I could use as my first Cloudron contribution: a privacy-first price-them-out CAPTCHA.
I hate the usability/accessibility nightmare that are traditional CAPTCHAs, especially now that essentially every method can be outsmarted by a cheap local LLM model. There were some promising PoW-based alternatives (Capjs, ALTCHA, mCaptcha, etc.), which I conceptually loved, but all of them either used a simple SHA-256-based puzzle (which is elementary to spammers who already have a bot farm) or had some other disqualifying feature for my preferences.
Necessity is the mother of invention, and so on, so I made my own!
https://codeberg.org/TheMeerkat/HeCAPTe
It uses an Equihash-based puzzle (if you're unfamiliar, think of it as Argon2 but extremely cheap to verify) and no visible widget users need to interact with. It's completely invisible as anything other than a small processing delay, and its cookieless and stateless nature means you don't need to disclose it to comply with privacy law.
I'll let the project's README speak for itself:
HeCAPTe provides a stateless spam-prevention mechanism that respects user privacy. Unlike traditional CAPTCHAs that rely on tracking user behavior or forcing users to complete busywork, HeCAPTe requires the user’s system to solve a computational puzzle (Equihash). This “Proof-of-Work” approach makes it computationally expensive for bots to generate mass requests while remaining quick for legitimate human users on modern devices.
- Humane: Requires no additional human interaction and presents no impediment to accessibility. Doesn’t try to extract value from the user by having them train image recognition models. Doesn’t infuriate vision-impaired users with audio from the first prototype of the telephone.
- Embeddable: Requires nothing more than one small Go binary, a few static files (including the .wasm solver), and an SQLite database. Even the cheapest VPS can run it without a hitch.
- Cost-Asymmetric: Expensive to solve, cheap to verify.
- Proof-of-work: HeCAPTe uses Equihash, a memory-hard proof-of-work algorithm. Unlike simple SHA256-based puzzles, Equihash's memory requirements make it significantly more costly to solve at scale; you can’t just throw more GPUs at the problem and call it a day, but my phone solves the puzzles about as quickly as my gaming laptop.
- Turing exam: Not quite a Turing test. Any one user submission is not, as per the original CAPTCHA vision, “proof” of humanity—but in a world with advanced OCR, services that have underpaid laborers type in answers for fractions of a penny, and even tiny local AI models that can easily solve most natural language puzzles, that vision is likely dead anyway.
Don’t try to barricade the way for bots and stop humans along the way; just make it more expensive to spam you than they could possibly get back as profit.
And then, since a Cloudron app was what I was trying to secure in the first place, packaging it for here just made the most sense.
https://codeberg.org/TheMeerkat/HeCAPTe-Cloudron
Now, extremely important warning:
This should be considered ALPHA STATE SOFTWARE.
I am not a professional programmer. I'm not even good at it. This is cobbled together with spit and broken dreams. I have verified that it works, doesn't cause any crazy disasters, that the Equihash logic is correct (for this simplified use case), that it has no neon-sign security holes, etc., but it's definitely missing basic comfort features I didn't personally care enough about to put in v1.0 and it hasn't exactly been through a battering ram of tests. Use this at your own risk!
Demo
The default demo page is up and running at https://hecate.eris.host/. Use the site ID dd0491eea14db55dfb87fcbc7197968c to test its default parameters. Now imagine it was a contact form, and "I am not a robot" was just labelled "Submit". I'd like to think that's a fair bit better of an experience than most security checks.
Install
Again: please see the bolded text about alpha state software.
To install as a Community App, enter this when requested:
https://codeberg.org/TheMeerkat/HeCAPTe-Cloudron/raw/branch/main/CloudronVersions.json
Contribute!
Please give me feedback on how useful you'd find this and any obvious issues you see with it! This thread is the only place I'm really advertising this to start with. If any actual-developers-for-real want to offer code contributions to the Codeberg repositories, I'd basically cry from pure elation. It's FOSS software!
Also, monetary support is never expected but always dearly appreciated.