Altcha — Rust Proof-of-Work Bot Protection Library

Altcha is the official Rust implementation of the ALTCHA Proof-of-Work (v2) protocol. It provides cryptographic challenge-response verification to protect web applications, forms, and APIs from bots and spam — without relying on CAPTCHAs that degrade user experience. The library is wire-compatible with the JavaScript ALTCHA widget, so a Rust backend can serve challenges that any ALTCHA JS frontend widget can solve.

This skill covers the altcha crate (v0.1.0+, MIT license, crate name: altcha). A separate community crate altcha-lib-rs exists but is less complete — focus on the official altcha crate from the altcha-org GitHub organization.

Crate Architecture

The crate is a single crate with no sub-crates. All public items are re-exported at the crate root: