Built a CAPTCHA alternative in C with PoW, JA4, and puzzle in complex mode
Captxa is a high-performance CAPTCHA server designed to combat bots using a proof-of-work challenge and a slider-puzzle challenge. It is built in C and can handle over 50,000 concurrent validations per second. The server features advanced security measures such as TLS fingerprinting and IP reputation filtering.
- ▪Captxa serves both simple and complex CAPTCHA challenges.
- ▪It is optimized for high concurrency and low latency.
- ▪The server requires a Debian Linux environment for deployment.
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Captxa — High-Performance CAPTCHA Server Captxa is a production-grade, anti-bot CAPTCHA engine written in C. It serves both a lightweight proof-of-work challenge ("simple") and a full slider-puzzle challenge ("complex") with mouse/touch trajectory analysis, TLS fingerprinting (JA4), GeoIP correlation, and IP reputation filtering. Zero-heap-allocation hot path. Sub-millisecond puzzle generation. Designed for 50k+ concurrent validations per second per core. Recommended hosting: Debian Linux server. How It Works See the full technical deep-dive at captxa.com/how_it_works.
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Excerpt limited to ~120 words for fair-use compliance. The full article is at GitHub.