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Trezor Bridge — Browser to Device Connector

Secure browser-based communication for hardware wallets

10-slide presentation • full-color • HTML + exportable to Office

Overview

Trezor Bridge acts as the bridge between your web browser and a Trezor hardware wallet. It handles USB/HID communication in a secure, cross-platform way so that web apps — like Trezor Suite or third-party dApps — can interact with the device without exposing private keys. This slide deck walks through architecture, installation, security considerations, common issues, and best practices.

Problem Statement

Why is a bridge necessary?

Modern browsers restrict low-level access to hardware devices for security reasons. To communicate with USB hardware like Trezor devices, a native intermediary is required. Trezor Bridge performs this role: it is a lightweight local service that provides a secure API for browsers to talk to the device via WebUSB, WebHID, or a custom protocol. Without Bridge, web pages would either be forced to implement fragile workarounds or ask users to install heavyweight, platform-specific drivers.

Bridges the gap between browser sandboxing and hardware access.
Ensures consistent behavior across Windows, macOS, Linux.
Reduces the attack surface by isolating hardware communication in a small, auditable process.

Architecture

How Bridge fits into the stack

Layers

Web app (dApp / Trezor Suite) — Initiates requests for signing, key derivation, and addresses.
Browser — Routes requests to Bridge using a local HTTP/WebSocket endpoint and browser APIs.
Trezor Bridge — Runs as a local service, exposes a JSON API, and forwards commands to the device via USB/HID.
Trezor device — Executes cryptographic operations inside secure firmware, returns signed payloads or confirmations.

Security boundaries

The security-critical operations remain on the device; Bridge only forwards messages. Bridge isolates USB drivers and provides permissioning prompts in the host OS, limiting attack vectors available to malicious web pages.

Installation & Setup

Getting started

Installing Bridge is straightforward. Official installers are provided for Windows (MSI/EXE), macOS (PKG), and Linux (DEB/RPM or AppImage). Many users are prompted to install Bridge the first time they connect a Trezor and open the web app. Key steps:

Download the official installer from Trezor's website.
Run the installer and accept any OS prompts for driver access.
Open your browser and navigate to your wallet/web app — Bridge should be detected automatically.

If the browser supports native WebHID/WebUSB for Trezor, Bridge may be optional; however, Bridge remains recommended for compatibility and consistent behavior.

Protocols & APIs

What Bridge exposes

Trezor Bridge exposes a local JSON-over-HTTP API and may use WebSocket for event-driven flows. It translates high-level transport calls into low-level USB/HID transactions. Important API characteristics:

JSON-RPC style requests for device discovery, firmware info, and command forwarding.
Support for enumerating devices and selecting a specific device when multiple are attached.
Versioning to avoid breaking changes for web apps.

Sample request flow

GET /api/v1/bridge/version
--> Bridge responds with {"version":"..."}
Web app then POSTs command packets for signing and receives responses.

Security Model

Threat model & mitigations

Trezor assumes a strong-device model: private keys never leave the hardware device, and sensitive operations require explicit user confirmation on the device. Bridge's responsibilities are intentionally limited:

Do not cache or store private keys.
Restrict access to local endpoints via OS-level permissions.
Sign and verify firmware and updates using cryptographic signatures.

For web apps, additional measures like origin checking and UI prompts prevent unnoticed transactions. Users should always verify transaction details on-device — not on-screen alone.

Troubleshooting

Common issues & fixes

Device not detected

Ensure Bridge is installed and running (check system tray / background services).
Try a different USB cable or port (some cables are power-only).
Restart the browser and the Bridge service.

Version mismatch

Update both Bridge and Trezor Suite/web app to latest versions.
Check Bridge logs for errors and consult support if needed.

Compatibility & Platforms

Supported environments

Trezor Bridge supports major desktop operating systems: Windows, macOS, and Linux. Mobile support is limited due to OS restrictions on USB host mode; where possible, mobile apps or Bluetooth bridges are used for mobile hardware wallets (note: Trezor devices historically rely on USB).

Browser compatibility: Chrome, Edge, and other Chromium-based browsers have best support for Bridge and WebHID/WebUSB. Firefox support varies and sometimes needs explicit settings or Bridge to be the primary transport.

Best Practices

Recommendations for users and devs

Users: Always verify addresses and amounts on the device screen. Keep Bridge and firmware up to date. Use official downloads only.
Developers: Use origin checks, proper request/response timeouts, and clear user prompts. Design web flows that minimize the chance of user error (display exact data that will be shown on-device).
Organizations: Provide internal guides for installing Bridge and maintaining update policies. Audit Bridge and related endpoints in penetration tests.

Conclusion & Resources

Wrap up

Trezor Bridge is a focused, minimal service that enables secure, cross-platform browser-to-device communication. It helps preserve a strong security model by keeping cryptographic operations on the device, while providing a reliable developer-facing API for web apps. Proper installation, up-to-date versions, and user vigilance complete the security stack.