The passkey authenticator in the core

Octa Pass passkeys are ordinary encrypted items, so the authenticator lives in the shared Rust core, where every app can use it. It’s built and tested; the browser extension that answers websites with it comes next.

What it does

• Creates passkeys with ES256 (P-256), or EdDSA (Ed25519) when the site prefers it. Each passkey has a random 16-byte credential ID and the Octa Pass AAGUID (c9a07734-1d0b-4c72-8ff5-45e0daa2064f), with attestation none.
• Signs in with the passkey you pick. Passkeys sync, so they’re reported as backed up and the signature counter stays 0.
• Refuses the wrong site. A page can only use a passkey for its own domain or a parent domain it could register: login.example.com can use example.com, but no page can use co.uk or github.io (checked against the Public Suffix List). Only https pages count (http://localhost for development), and a site inside another site’s frame needs your permission first.
• Stores passkeys inside logins. A new passkey goes into the login for the site, or a new login named after it. The private key is kept only in the login’s encrypted details, as a standard PKCS#8 key, and the passkey calls never hand it to JavaScript.
• Moves passkeys to and from the FIDO Credential Exchange Format (CXF), one passkey at a time, ready for the importers and exporters.

How it’s tested

Every passkey the core creates is checked by a relying-party verifier written from the WebAuthn specification with separate CBOR and COSE parsers, and, through WebAssembly, by Node’s OpenSSL. Test vectors for both algorithms are in crates/octapass-core/tests/vectors/passkey.json. See passkeys for what websites see.