extension

Passport Prime Nostr Signer — Browser Extension (1.3 / WebUSB build)

Chromium browser extension that implements the NIP-07 window.nostr surface on top of the Passport Prime signer. The nsec never leaves the device; this extension only relays signing requests. Auto-sign rules, when used, are configured on Passport Prime and are not editable from the extension.

This is the 1.3 build: the hardware transport is WebUSB, matching the KeyOS dev-v1.3.0 port of gui-app-nostr-signer which registers a vendor-class interface (class/subclass/protocol = 0xFF/0xFF/0xFF) with two 64-byte Interrupt endpoints.

Two transports

Selectable on the options page:

• WebUSB (default) — navigator.usb to a physical Passport Prime. First-time pairing requires the Chromium WebUSB picker (a user gesture), which you initiate from the options page.
• WebSocket — ws://127.0.0.1:9876, served either by the standalone signer binary on your Mac or by the KeyOS hosted-mode simulator. Flip the "simulator mode" checkbox in Settings to switch.

Install (dev mode)

1. Flash Prime with a KeyOS build that includes gui-app-nostr-signer on the qna/nostr-signer-1.3 branch. Open the Nostr Signer app on Prime and add a key.

2. Open chrome://extensions, enable Developer mode, click Load unpacked, and select this extension/ directory.

3. In the extension's Settings page, click Pair Passport Prime and select your Prime in the system WebUSB picker.

4. Visit any Nostr client that supports NIP-07 (e.g. noStrudel, Snort) and pick the "Sign in with extension" option. On first use, open the extension popup and allow that site origin before retrying the client action.

Architecture

page script  ──window.postMessage──  content.js ──chrome.runtime── background.js
 (inpage.js)                                                              │
                                                                          ▼
                                                             ┌──────────┴──────────┐
                                                             │                     │
                                                       WebSocket              WebUSB
                                                             │                     │
                                                             ▼                     ▼
                                                       signer binary        Passport Prime
                                                       or simulator         (hardware, 1.3)

Wire format is newline-delimited JSON on both transports. On WebUSB the browser chunks payloads into 64-byte transferOut calls and accumulates transferIn results until it sees a \n.

The provider is injected broadly into HTTP/HTTPS pages for NIP-07 compatibility, but requests fail closed until the user allows the exact site origin in the extension popup. A device-local auto-sign rule can skip the on-device approval screen only for the exact key/origin/kind/expiry/rate-limit policy configured on Prime. Use Settings → Reset extension state to clear paired USB devices, selected key, and site permissions during demos.

License

GPL-3.0-or-later.