punktfunk/docs-site/content/docs/pairing.md

---
title: Pairing & Trust
description: How a client and host establish trust — PIN pairing once, pinned reconnects after.
---

punktfunk has no accounts and no cloud. Trust is established directly between a client and a host,
on your network, with a one-time pairing — either an **approval click in the host's console** or a
**PIN ceremony**. After that, the device reconnects automatically on a pinned cryptographic
identity.

## How it works

- Each host has a stable **identity** (a certificate). Clients remember its fingerprint, so they know
  they're talking to the same host next time.
- The first time a client connects, you **pair** it: the host shows a short **4-digit PIN**, you type
  it into the client, and a secure exchange (SPAKE2) binds the two identities. An attacker who doesn't
  know the PIN gets a single online guess — no offline cracking.
- After pairing, the host stores the client's identity in its allow-list, and the client stores the
  host's fingerprint. Reconnects are automatic — no PIN.

## Approving a device from the console (no PIN)

The fastest way to admit a new device: just **try to connect** from it. On a pairing-required host,
the attempt shows up in the web console's Pairing page under **Waiting for approval** — with the
device's name and identity fingerprint. Click **Approve** (and optionally give it a label like
"Living Room TV"), and the device is paired on the spot: its next connect goes straight through. No
PIN to read or type.

**Deny** just dismisses the request (the device can knock again later — it's "not now", not a
blocklist). Requests expire on their own after a few minutes.

This works because approval happens on the host's authenticated management surface — only someone
with console access can admit a device.

## Pairing with a PIN

PIN pairing is the **default and required** path for any new host: unless the host has explicitly
opted into trust-on-first-use (see below), a client connecting to an unknown host must complete the
PIN ceremony before it can stream. It's the right path for the *first* device (before the console has
admitted anything) or when you're at the client and the console isn't handy.

Pairing has to be **armed** on the host before a client can pair (so a random device can't pair
itself). On the production host (`serve`), this is done from the **web console**: open the
host's management console, click to arm pairing, and the host displays a 4-digit PIN along with the
list of paired devices. This works on a headless host over the network — there is no command-line flag
to arm pairing on `serve`.

(The standalone headless test host, `punktfunk1-host`, requires pairing by default too and takes
`--allow-tofu` on its command line to accept unpaired clients; the production `serve` host arms
pairing from the console.)

Then, on the client:

- **Native clients (Apple, Linux, Windows, Android):** select the host (or use *Pair with PIN…* from
  its menu) and enter the PIN the host displays.
- **Moonlight:** choose **Pair**; Moonlight shows the PIN to confirm on the host side.

## Requiring pairing (the default)

By default, the native host **requires** pairing — only devices that have paired can stream. This is
the right setting on a shared network: a device has to complete the PIN ceremony once before it can
connect.

If you're on a fully trusted single-user network and want to skip pairing, run the host open with
`serve --open` (or `punktfunk1-host --allow-tofu` for the standalone host) — it then advertises
`pair=optional` and accepts unpaired clients. Requiring pairing is strongly recommended.

## Trust-on-first-use (host opt-in)

Trust-on-first-use (TOFU) is **off by default** and is an explicit *host* opt-in for fully trusted
networks. A host enables it by running open — `punktfunk1-host --allow-tofu` or `serve --open` — which makes
it advertise `pair=optional` over mDNS and accept unpaired clients. Only then does a client offer the
TOFU path: connecting to such a host for the first time shows the host's fingerprint and asks you to
confirm it (compare it with the one the host logged at startup), then pins it. The client presents
this clearly as the reduced-security option, alongside **Pair with PIN**.

> **Warning:** TOFU cannot detect an impostor on the first connection — if someone is impersonating
> the host the very first time you connect, you'll pin the attacker's fingerprint. PIN pairing closes
> that gap (the SPAKE2 ceremony binds both identities), which is why it's the default. Use TOFU only
> on a network you fully trust.

For every other case — a host advertising `pair=required` (the default), a host you typed in by hand,
or a discovered host whose pair policy is unknown — TOFU is not offered and the client routes straight
to the PIN ceremony.

Once a host is pinned, a fingerprint change is treated as the impostor signal: the client forces
re-pairing through the PIN ceremony rather than offering to re-trust the new identity.

## Managing paired devices

The web console lists every paired device and lets you remove one (revoking its access). Re-pairing is
just the PIN ceremony again.