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

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Pairing & Trust	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 web 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: with the native protocol the host shows a short 4-digit PIN and you type it into the client. (With Moonlight it runs the other way round — Moonlight shows the PIN and you type it into the host's console.) Either way a secure exchange (SPAKE2) binds the two identities, and 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. Having seen the host on your network while it was awake also teaches the client its MAC address, so a later connect can wake it from sleep.

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 10 minutes.

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

Choosing access when you admit a device

Admitting a device and deciding what it may do are one dialog, not two trips. The Approve dialog carries, alongside the device's name:

• Access level — Full control, Controller only, or View only, with an Advanced expander for the individual toggles. See Access levels for exactly what each covers.
• Expires — Forever, or 1 h / 4 h / 8 h / custom.

The defaults are Full control · Forever — approving your own new laptop is the common case, and it should behave like pairing always has. The guest case gets its own button instead: a distinct secondary action, "Approve as guest", admits the device as Controller only for 4 hours in one click. The whole co-play flow is: your friend installs a client, connects, the knock appears in your console, you tap Approve as guest — and their pad lights up as controller #2. When the evening's over, the access expires on its own.

The same two controls appear on the arm pairing card for the PIN path: whatever access and expiry you choose while arming applies to whichever device completes the PIN ceremony in that window.

Everything here can be changed later from the Paired devices table — see Managing paired devices below.

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 — or be approved from the console, as above — 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 armed window lasts 2 minutes — the console counts it down under the PIN and offers a Cancel button. Arm it once you're standing at the device; if it lapses, just arm it again.

Pairing from the console needs the console running. On Linux that's the separate punktfunk-web systemd user unit, which you enable once — see The Web 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.
• Steam Deck (the Decky plugin): open Punktfunk from the Quick Access menu and pick the host — an unpaired one opens a sheet offering Request access (no PIN: somebody approves the Deck at the host) or Use a PIN instead, which opens the 4-digit pad.
• Moonlight: choose Pair; Moonlight shows a 4-digit PIN, and you type that PIN into the console's Moonlight (GameStream) pairing card and press Submit PIN. (This direction is the reverse of the native flow, and arming doesn't apply to it.)

A link can't stand in for any of this. A punktfunk:// link starts a stream on a host this device already trusts; punktfunk://pair/… is refused outright, and a link naming a host you've never paired with can at most open the app's own trust prompt.

Pairing from a terminal

On Linux the client package also installs punktfunk, a headless CLI. Arm pairing in the console, read the PIN, then run:

punktfunk pair 192.168.1.50 --pin 1234 --name "Living Room"

It prints paired <addr>:<port> fp=<fingerprint> and saves the host in the same store the desktop client uses, so later connects are silent. --name is the label the host files this device under (default: this machine's name), and the port defaults to 9777 — write host:port to use another one. Without --pin the command asks for one; in a script with no terminal it exits 6 rather than hanging, and exit 3 means the host refused or the PIN was wrong.

The GTK client can do the same thing without opening a window:

punktfunk-client --connect 192.168.1.50:9777 --pair 1234 --name "Living Room"

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 — 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 — 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 — see Security & Safe Use.

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). Each row also shows the device's Access — the preset and, for temporary grants, a live countdown ("Controller · 2 h left") — and an edit sheet to change the level, extend or cut the expiry, or expire it right now; edits reach a live session immediately. See Access levels. Re-pairing is just the PIN ceremony again — and it keeps the device's existing access rather than widening it.

If a client can't pair at all, see Troubleshooting → Pairing is rejected.

(There is also a developer/measurement host, punktfunk-host punktfunk1-host — a subcommand of the same binary, not the host you install. It has its own --allow-tofu / --pairing-pin flags for test harnesses; nothing on this page applies to it.)