P-Captcha

P-Captcha is a lightweight, open-source CAPTCHA solution that uses proof-of-work to protect against bots. It's self-hosted, has zero dependencies, and is developer-friendly.

Features

- 🪶 Truly Lightweight - Zero dependencies, only 2KB gzipped, powered by Web-workers
- 🎨 Fully Customizable - Easy to override styles and customize behavior
- 👥 User-Friendly - Supports both invisible and one-click verification modes

Protection Against

- 🚫 Spam - Secure forms from spam and automated submissions
- 🤖 Scraping and Automation - Protect content from scraping and platform abuse
- 🛡️ DDoS - Guard compute-expensive API endpoints
- 🔒 Account Takeover - Prevent credential stuffing and brute force attacks

Live demo: https://p-captcha.com/#demo

[![P-captcha Demo]](https://github.com/user-attachments/assets/8d5cc70a-ce2a-40fa-a258-e6436a467cc1)

Quick Start

$3

``bash
npm install @p-captcha/node
`

$3

`bash
npm install @p-captcha/react
`

$3

`javascript
import { InMemoryCaptchaService, WoodallAliases } from "@p-captcha/node";

const captchaService = new InMemoryCaptchaService();

app.get("/api/challenge", (req, res) => {
const { challenge, id } = captchaService.generateChallenge(
"QuadraticResidueProblem",
{
woodall: WoodallAliases.md,
rounds: 2,
}
);
res.json({ challenge, id });
});
`

$3

`javascript
import { PCaptchaWidget, PCaptchaWidgetInvisible } from "@p-captcha/react";

challenge={challenge}
onVerified={(solution) => {
validateOnServer(solution);
}}
/>

/ Or use invisible component that solves challenge when mounted /

challenge && (
challenge={challenge}
onVerified={(solution) => {
validateOnServer(solution);
}}
/>
)
`

$3

`javascript
app.post("/api/validate", (req, res) => {
const { answer, id } = req.body;
const success = captchaService.validateAnswer(id, answer);

if (!success) {
res.json({ text: "Invalid captcha!" });
return;
}

res.json({ text: "Form processed correctly, captcha is valid!" });
});
`

Customization

$3

`javascript
captchaService.generateChallenge(
"QuadraticResidueProblem",
{
woodall: WoodallAliases.md,
rounds: 2,
}
);
`

rounds: How many problems user needs to solve

woodall: Woodall prime number size controls problem difficulty

| Woodall Prime number | Alias | Bits | Time on Apple M2 Pro* |
| -------------------- | ----- | ----- | --------------------- |
| 751*2^751-1 | 2xs | 761 | ~80 ms |
| 83*2^5318-1 | xs | 5322 | 238 ms |
| 7755*2^7755-1 | sm | 7765 | 598 ms |
| 9531*2^9531-1 | md | 9542 | 931 ms |
| 12379*2^12379-1 | lg | 12387 | 1995 ms |
| 7911*2^15823-1 | xl | 15830 | 3466 ms |
| 18885*2^18885-1 | 2xl | 18891 | 5581 ms |
| 22971*2^22971-1 | 3xl | 22974 | 9199 ms |
____
\*Average time of 10 runs solving quadratic residue problem with Tonelli-Shanks algorithm

$3

Out-of-the-box @p-captcha/node provides in memory service. But you can easily compose a service with any KV database like Redis. All you need to do is to implement this interface:

`javascript
interface CaptchaStorage {
saveItem: (key: string, value: string) => IsSuccess;
getItem: (key: string) => string | null;
removeItem: (key: string) => IsSuccess;
}
`

$3

Widget provides className overrides of all significant elements and allows you to override spinner and success (checkmark) elements.

`javascript
type PCaptchaWidgetProps = {
onVerified: (solution: string) => void;
challenge: string;
label?: string;
onSubmit?: () => void;
classNameOverrides?: {
container?: string;
checkbox?: string;
spinner?: string;
text?: string;
};
renderSpinner?: () => React.ReactNode;
renderSuccess?: () => React.ReactNode;
};
``