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Security and Onboarding

QAROS deployments often run on factory floors, in hospitals, and on corporate networks — places where "trust the LAN" is not acceptable. The security model is therefore built on a simple promise: a short pairing code, typed once, bootstraps a full cryptographic identity — and the code itself never travels over the network.

The four layers​

Security layers

Layer 0 — Discovery (open by design)​

Devices find the Hub with zero configuration: the Hub broadcasts a beacon on the local network (UDP multicast 239.77.77.77:7445) and answers discovery requests on TCP 7445. This layer is deliberately unauthenticated and carries no secrets — only coordination metadata (device name, invitation nonce, server ID, where to reach the pairing service). A forged beacon can at worst redirect a connection attempt; pairing still fails without the correct code.

Layer 1 — Pairing (EC-JPAKE)​

The Hub issues short-lived pairing codes (8 characters from a no-look-alike alphabet). A user transfers the code out-of-band — reads it off the Hub's screen, scans a QR, or pastes it. Device and Hub then run EC-JPAKE (a password-authenticated key exchange on P-256): each side proves it knows the code without ever transmitting it. What actually protects the deployment is not code length but code handling:

  • every code is single-use — consumed on success and on failure,
  • codes expire after 10 seconds (the Hub mints a fresh one every few seconds),
  • one failed attempt invalidates the invitation,
  • the Hub's server ID is bound into the exchange, so a code for one Hub can never be replayed against another.

A successful exchange yields a strong shared key.

Layer 2 — Secure channel and enrollment (AES-256-GCM)​

The shared key encrypts a private channel (AES-256-GCM, separate keys per direction, fresh nonces). Over this channel — and only now — the real credentialing happens:

  1. The Hub sends an enrollment offer: the device's assigned name and the Hub's CA trust bundle.
  2. The device generates a key pair locally and sends a certificate signing request (CSR). The private key never leaves the device.
  3. The Hub's CA gateway validates the request and has the Hub's private CA sign a certificate. Crucially, the certificate's identity content (names, peer and session bindings) is derived from the authenticated channel — not from whatever the CSR claims.

Layer 3 — Session traffic (mutual TLS)​

All session communication runs over the Zenoh messaging bus on TCP 19120-19200 with mutual TLS: both sides present their Hub-issued certificates. Hub, launched apps, and devices run as Zenoh peers, connecting to known endpoints and listening for full-mesh peer links in that bounded range. From this point on, pairing codes play no role - identity is the certificate, and rejoining after a restart is silent.

The per-Hub Certificate Authority​

Each Hub operates its own private CA (based on step-ca). This means:

  • No external dependency. A deployment is self-contained; no internet, cloud, or corporate PKI is required.
  • The Hub is the trust root. A certificate from Hub A means "Hub A vouched for this device". The Hub machine itself is assumed trusted — protect it as you would a domain controller.
  • Renewal is online and CSR-based: a device with a valid certificate can refresh it without re-pairing. A certificate that expires while the device is offline requires onboarding again.
  • Revocation is two-layered: the CA can revoke, and the gateway keeps an encrypted blacklist. A blacklisted device can only return through a fresh, human-approved pairing.

Hub-to-Hub federation​

When two Hubs connect, they exchange and merge CA trust bundles. Devices onboarded to Hub A are then accepted by Hub B and vice versa — federated trust. Signing stays local: each Hub only ever issues certificates for its own devices.

What this means for each audience​

For users: you type a short code once per device. Everything after that is automatic — reconnecting later needs no code.

For operators: the security perimeter is (1) the Hub machine, and (2) whoever can see the pairing screen for the 10 seconds a code lives. Network eavesdroppers learn nothing useful from discovery, and cannot join without a code.

For application developers: the entire stack above is hidden behind three C API calls — onboard, rejoin, and forget. Your app persists one opaque onboarding ID and never touches keys or certificates. See Onboarding and Sessions.