Hardware keys and passkeys

What is supported

Signature scheme 2: WebAuthn / ECDSA P-256. The web wallet can create a key inside a security key (YubiKey and similar FIDO2 keys), a platform authenticator (Touch ID, Windows Hello, Android biometrics) or a phone passkey. The private key never leaves the device and every transaction requires the user's touch or biometric.

How it works on-chain (src/crypto.js verifyWebAuthn, src/tx.js):

• Address = bech32(scheme byte 2 ‖ sha256(2 ‖ publicKey)[0:20]); the public key is the uncompressed P-256 point (65 bytes). A transaction carries scheme: 2, that pub, and sig = {authData, clientData, signature}.
• The wallet asks the device to sign the challenge sha256(signingBytes(tx)). The chain checks: clientData.type == "webauthn.get"; clientData.challenge == base64url(sha256(signingBytes(tx))) (so a signature is bound to the exact transaction, chain ID and nonce, and cannot be transplanted); the user-present flag is set; and the ECDSA signature over authData ‖ sha256(clientData) verifies under the account's key.
• Recovery can move any account onto a hardware key: guardians approve recoveryApprove {account, newPub, newScheme: 2}.

Things to know

• Not exportable, so use guardians. A hardware key cannot be backed up. Losing the device loses the key; set guardians (Security tab) so the account can be recovered to a new key.
• Bound to the site name. WebAuthn credentials are scoped to the host name (relying-party ID) of the page that created them (for example app.auren.im). They cannot be used from another host name, which is also what stops a phishing site from asking your key to sign.
• Secure pages only. Browsers expose WebAuthn only on secure (HTTPS) pages. The AUREN apps and website are secure.
• Signature size: about 200-300 bytes more than Ed25519 per transaction (authenticator data + client data). Fine at current block limits; this is a measured trade-off, not free.
• Approval prompt shows less than the review screen. The device usually shows only "sign in to <site>". The wallet's review dialog (with the node's dry-run) is the place where you check amounts and recipients, then the touch confirms.

Ledger and Trezor

Not supported yet, and this is a hard external dependency, not a missing feature flag. A Ledger signs only through an app installed on the device, and no AUREN app exists. Building one means writing and submitting device firmware (C, Ledger SDK) and passing Ledger's review; it cannot be verified without a physical device. WebAuthn gives the same property (key never leaves hardware, user confirmation per transaction) with devices people already own. A Ledger app is on the roadmap for after the transaction format is frozen.

Testing, and what is not covered

test/webauthn.test.js verifies the chain-side logic with real P-256 cryptography and the exact byte formats a browser returns, via a software authenticator: acceptance and execution, rejection when the amount, nonce or chain ID changes, rejection of a signature transplanted from another transaction, rejection without user presence, parity of address derivation between the browser library and the node, and guardian recovery onto a hardware key (old key stops working).

Not covered by automated tests: a physical security key or biometric prompt (a test runner cannot touch a YubiKey), and browser-specific differences. Manual checklist before relying on it:

1. Open the wallet (website or app) in current Chrome, Edge, Safari or Firefox.
2. "Hardware key / passkey" → create; the device prompts; the wallet shows an address.
3. Fund it from the faucet; send a transaction; the device prompts; the transaction confirms.
4. Set a guardian, and complete a recovery to another key.
5. Repeat with a second authenticator type (platform vs. USB key).

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