whipair prototype

whipair is a direct, one-shot SSH public-key enrollment prototype for Whip. By default it uses the host's existing SSH port: no relay, TLS listener, additional firewall rule, pairing account, or sshd_config change is required.

The host creates a temporary Ed25519 credential and adds only its public half to the current user's authorized_keys with restrict and a forced command. The QR contains the private seed, SSH endpoint, username, and SSH host-key pin. Whip uses that credential for one restricted exchange, the host user approves the submitted permanent public key, and whipair removes the temporary authorization.

Install

All non-Nix installations require ssh-keyscan from an OpenSSH client package to be available on PATH.

uv

Run the native binary from PyPI without installing Rust:

uvx whipair

uvx is an alias for uv tool run; either form creates an isolated tool environment and runs whipair. Published wheels support macOS and Linux on ARM64 and x64.

npm

Run the native binary from npm without installing Rust:

npx whipair

The npm package is a dependency-free launcher containing the same four native binaries. Node.js 18 or newer is required.

Cargo

Install the published crate with Rust 1.99 or newer:

cargo install --locked whipair
whipair

Source builds use the same pinned Rust toolchain as Whip. The repository's rust-toolchain.toml links to the mobile Rust core's toolchain file; Nix and the release workflows use that pin too.

Nix

Run the public version:

nix run github:kosumic/whip#whipair

Without arguments, whipair lists the host's reachable interface addresses, uses ifconfig.me to discover its public IP when curl is available, and also offers a manual public-address choice:

Choose how Whip will reach this host:

  1. Tailscale    100.84.12.5                             tailscale0
  2. Wi-Fi        192.168.1.20                            wlan0
  3. Public       203.0.113.10                            ifconfig.me
  4. Public/other Enter a public IP address or hostname
  5. Tailcat      Enter a Tailcat tc address

Selection [1]:

Public-IP discovery does not verify that SSH is reachable through the router or firewall. Choose Public/other to enter a DNS name or a different address, or select a specific reachable endpoint non-interactively:

nix run github:kosumic/whip#whipair -- serve \
  --advertise-host 192.168.1.10

If SSH is already listening on a nonstandard port, advertise it with --ssh-port:

nix run github:kosumic/whip#whipair -- serve \
  --advertise-host ssh.example.com \
  --ssh-port 2222

--ssh-port defaults to 22. It does not open a new port; it must match the existing SSH service reachable at the advertised host. When no --advertise-host is supplied, the interactive setup asks for the endpoint and port, offering 22 as the default. Passing both options skips those questions. whipair does not bind a TCP listener; Whip connects to the host's existing SSH service.

Choose Tailcat, the last interface option, to paste a tc… address from a running Tailcat server forwarding to the host's existing SSH service. Whip recognizes the transport from the QR, pairs over Tailcat, and saves the address and client identity for subsequent connections. No Tailcat toggle is needed on the Add Host screen. Tailcat pairing connects directly to the tunnel and cannot use a jump host.

You can also supply the address without the interface prompt:

whipair serve --tailcat-address 'tc…' --ssh-port 22

The port must match the SSH port forwarded by Tailcat. Whipair discovers the SSH host key through 127.0.0.1 for this option; use --ssh-fingerprint if sshd is bound to a different local address. Whipair's one-time authorization requires the host's existing sshd. The development request client supports direct SSH codes; scan Tailcat codes with Whip.

For a public endpoint behind NAT, forward the advertised public port to the host's SSH port and allow that SSH port through the relevant router, host, or cloud firewalls. If the host cannot reach its own public endpoint because the router lacks NAT loopback, automatic ssh-keyscan discovery will fail. Read the local Ed25519 host-key fingerprint and pass it explicitly:

ssh-keygen -lf /etc/ssh/ssh_host_ed25519_key.pub -E sha256

nix run github:kosumic/whip#whipair -- serve \
  --advertise-host ssh.example.com \
  --ssh-port 2222 \
  --ssh-fingerprint 'SHA256:...'

From a local checkout:

nix run .#whipair

The Nix app includes ssh-keyscan. Automatic discovery requests Ed25519, ECDSA, and RSA host keys in Whip's russh preference order. Use --ssh-fingerprint to provide a fingerprint explicitly.

During development, print the underlying envelope:

nix run .#whipair -- serve --advertise-host 192.168.1.10 --print-code

Exercise the SSH-only protocol with a disposable public key:

nix run .#whipair -- request \
  --code 'WP4:...' \
  --public-key ~/.ssh/id_ed25519.pub \
  --device-name 'Prototype client'

Inspect a copied envelope without exposing its temporary private seed:

nix run .#whipair -- inspect 'WP4:...'

Prototype limitations

• The SSH server must use OpenSSH-compatible authorized_keys, support the restrict and command options, and read the current user's default ~/.ssh/authorized_keys file.
• The interactive network selector uses curl to offer the public IP reported by ifconfig.me when available. Failure to fetch it does not block pairing.
• Automatic host-key discovery invokes ssh-keyscan; the Nix app supplies it. The Nix app also supplies curl for public-IP discovery.
• The terminal QR uses error-correction level L to stay compact.
• Whip's mobile scanner supports WP4. The request subcommand remains a protocol test client.

Pairing protocol (WP4)

The canonical Mermaid source is docs/wp4-sequence.mmd. Render and validate the tracked SVG with:

nix shell nixpkgs#mermaid-cli -c mmdc \
  -i whipair/docs/wp4-sequence.mmd \
  -o whipair/docs/wp4-sequence.svg

QR bootstrap envelope

The QR contains WP4: followed by Base45-encoded binary data.

For an IPv4 address and a five-character username, the complete code is 120 characters and renders as a 37-module QR at error-correction level L. Expiry is enforced by the running host process and is intentionally omitted. Tailcat addresses may contain up to 1024 ASCII bytes and produce larger QR codes. Whip validates the complete Tailcat address before contacting a relay.

Host authorization and exchange

Before displaying the QR, whipair adds an entry equivalent to:

restrict,command="whipair exchange --socket …" ssh-ed25519 AAAA… whipair-temporary

restrict disables shell access, PTY allocation, forwarding, agent forwarding, X11, and user startup commands. The forced command accepts one bounded JSON EnrollmentRequest on SSH stdin and relays it through a Unix socket in a mode-0700 temporary directory to the visible whipair process.

The parent process validates the submitted OpenSSH public key and displays a six-digit verification code derived from its SHA-256 fingerprint. Whip shows the same code while it waits, so the user can compare the phone and host before approving. Approval is bounded by the invitation TTL. On approval the host appends the permanent key safely and idempotently, replies with an EnrollmentResponse, removes the temporary entry, and exits. Rejection leaves the one-shot invitation available until its TTL expires.

Whip verifies the SSH host key against the digest in the QR before sending any enrollment data. After pairing, it stores the verified public host key in its global known-hosts list, so the saved host does not require a second trust prompt.

Security properties and boundaries

• The QR is a short-lived bearer credential. Anyone who can scan it and reach SSH can request enrollment, but the key can invoke only the forced exchange command and the host still asks for approval.
• WP4 transfers a temporary private-key seed, never the private half of the permanent key being enrolled. Normal SSH authentication later proves possession of that permanent key.
• The temporary key is removed on success, expiry, or Ctrl-C. If the process is killed before cleanup, the leftover entry remains restricted and its forced command cannot connect to the vanished private Unix socket.
• Bare OpenSSH public keys understood by Whip's ssh-key parser are accepted. authorized_keys options are rejected, comments are preserved, and duplicate permanent keys are not appended.
• The writer refuses symlink targets and files not owned by the current user, serializes every update through a stable adjacent lock file, uses atomic replacement for removal, and creates .ssh and authorized_keys with modes 0700 and 0600 when needed.

Publishing

The Publish whipair to crates.io workflow verifies the crate version, formatting, Clippy, tests, and package contents before publishing. Crates.io trusts only publish-whipair.yml in kosumic/whip with the protected crates-io environment. The workflow uses a short-lived OIDC credential; GitHub stores no crates.io API token.

The Publish whipair to PyPI and npm workflow builds native PyPI wheels and npm binaries for macOS and Linux on ARM64 and x64. PyPI should trust publish-whipair-packages.yml with the pypi environment. After the first npm release, npm should trust the same workflow with the npm environment. Both registries then publish with short-lived GitHub OIDC credentials and provenance instead of stored tokens.

PyPI supports a pending trusted publisher for the first release. npm requires the package to exist before trusted publishing can be configured, so add a short-lived NPM_TOKEN secret to the protected npm environment, manually run the workflow once with Publish the npm package and Bootstrap the first npm release with NPM_TOKEN enabled, configure npm trusted publishing, and then delete the secret.

To release a version, update version in whipair/Cargo.toml, whipair/npm/package.json, and the mkWhipair version in flake.nix, refresh whipair/Cargo.lock, and run:

nix develop -c cargo test --locked --manifest-path whipair/Cargo.toml
nix develop -c cargo publish --locked --dry-run \
  --manifest-path whipair/Cargo.toml
nix develop -c uvx maturin build --release --locked \
  --manifest-path whipair/Cargo.toml \
  --out whipair/dist

Commit those changes, then push a tag whose version matches Cargo.toml exactly:

git tag whipair-v0.1.4
git push origin whipair-v0.1.4