{"categories":[{"label":"Cryptography","url":"https://skillfed.io/packages/category/security-cryptography/2"}],"enrichment":{"capability":"Creates and verifies ALTCHA proof-of-work challenges using key derivation functions like PBKDF2, Argon2id, and scrypt to defend against automated attacks.","skillfed_tags":["proof-of-work","bot-protection","cryptography"],"use_cases":["Protect web forms and APIs from bot submissions by requiring clients to solve a proof-of-work challenge before accepting requests.","Implement rate limiting or anti-spam mechanisms that are resistant to GPU-accelerated attacks using memory-hard algorithms.","Verify that a client performed computational work before granting access to expensive resources or rate-limited endpoints.","Embed tamper-proof challenges in web applications by signing them with HMAC and verifying the signature server-side.","Test proof-of-work implementations quickly using fast SHA-based algorithms without deploying memory-hard variants."],"what_it_does":"ALTCHA is a zero-dependency Python library for creating and verifying proof-of-work challenges designed to protect against automated attacks. It implements PoW v2, which uses key derivation functions (KDFs) instead of simple hash matching\u2014clients must find a counter value whose derived key starts with a required prefix. The library supports multiple algorithms: fast iterated SHA variants for testing, PBKDF2 for general use, and memory-hard algorithms like scrypt and Argon2id that resist GPU/ASIC attacks.\n\nThe typical workflow is server-side: create a challenge with a chosen algorithm and cost, send it to the client, which solves it by brute-forcing counter values, then transmit the solution back to the server for verification. The library handles challenge expiry, optional HMAC signing for tamper detection, and a fast verification path when you pre-solve challenges server-side. It also supports custom KDF functions and server signature verification via the ALTCHA Sentinel API.","worth_installing":"Yes. The library is actively maintained, has zero runtime dependencies, installs easily, carries no known vulnerabilities, and solves a real problem (bot protection via proof-of-work). It is permissively licensed and supports current Python versions. Install it if you need ALTCHA challenge generation and verification; the API is straightforward and the documentation includes working examples."},"id":"altcha","links":{"html":"https://skillfed.io/packages/altcha","md":"https://skillfed.io/packages/altcha.md","pypi":"https://pypi.org/project/altcha/"},"maintenance":{"status":"active"},"meta":{"latest_release":"2026-07-27","license_spdx":null,"license_treatment":"permissive","name":"altcha","python_support":"supports_current","summary":"A library for creating and verifying challenges for ALTCHA."},"popularity":{"monthly_downloads":296462,"position":7897,"tier":"top_15000"},"security":{"n_vulnerabilities":0},"version":"2.1.0"}