---
id: pyu2f
version: "0.1.5"
license: Apache 2.0
license_treatment: permissive
maintenance: abandoned
---

# pyu2f — U2F host library for interacting with a U2F device over USB.

License: permissive · Maintenance: abandoned · Downloads: 442.6K/mo

## What it is and what it does

pyu2f is a Python library for communicating with U2F (Universal 2nd Factor) security keys over USB. It uses ctypes to call system USB HID APIs directly, avoiding the need for platform-specific compiled libraries. The library implements a U2F stack for signing authentication challenges and supports pluggable authenticators via the SK_SIGNING_PLUGIN environment variable.

The package is no longer maintained; its repository is archived and the authors explicitly recommend migrating to python-fido2, which supports the newer FIDO2 standard and provides backward-compatible U2F support. U2F itself is considered an outdated FIDO specification. If you are starting a new project, this library should not be your first choice.

Use it for:

- Authenticate users with legacy U2F security keys in existing Python applications on Windows, macOS, or Linux.
- Integrate U2F device support into a Python authentication system without requiring compiled platform-specific libraries.
- Offload U2F signing operations to an external command-line tool via the SK_SIGNING_PLUGIN mechanism.

## Worth the install?

AI-flagged interpretation of the facts above — verify before relying.

pyu2f provides U2F (Universal 2nd Factor) device authentication over USB on Linux, Windows, and macOS using ctypes-based system calls without compiled dependencies.

No. The package is abandoned, its repository archived, and the maintainers explicitly recommend python-fido2 instead. U2F is an outdated FIDO spec. Install only if you must maintain legacy code already using pyu2f; for new projects, use python-fido2.

## Install

pip install pyu2f
uv add pyu2f
poetry add pyu2f

## Installing pyu2f

Before you install: High install friction due to source distribution only. Maintenance is abandoned as of 2020-10-30; the repository is archived and the maintainers recommend migrating to python-fido2 for FIDO2 support and ongoing security updates.

License in practice: Apache 2.0 is permissive; you may use, modify, and distribute this code freely provided you retain license notices and do not hold the authors liable.

Quickstart:

from pyu2f import model
from pyu2f.convenience import authenticator

registered_key = model.RegisteredKey(b64_encoded_key)
challenge_data = [{'key': registered_key, 'challenge': raw_challenge_data}]
api = authenticator.CreateCompositeAuthenticator(origin)
response = api.Authenticate(app_id, challenge_data)

Requires a U2F-compatible USB device connected to the system; SK_SIGNING_PLUGIN environment variable can optionally redirect signing to an external tool.

Verify before relying:

- Whether the ctypes-based USB HID calls work reliably on modern versions of Windows, macOS, and Linux kernels.
- Current compatibility with modern U2F devices and whether deprecated U2F protocol support poses a security risk in production use.

## Package facts

- License: Apache 2.0 (permissive)
- Python support: unspecified
- Install friction: high
- Maintenance: abandoned
- Downloads: 442.6K/month (top 15,000 on PyPI)
- Known vulnerabilities: none known

## Tags

U2F authentication library, USB security key support, two-factor authentication device, FIDO U2F host library, hardware security token python, deprecated, u2f, security-key

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