Trezor Bridge — secure connectivity for hardware wallets

What is Trezor Bridge?

Trezor Bridge is a lightweight local application that enables web browsers to communicate with Trezor hardware wallets (Trezor One, Trezor Model T) over USB. It acts as a secure bridge between client software (web wallets, browser-based apps) and the device, translating requests into device-compatible operations while isolating USB access from the browser sandbox.

The purpose of Bridge is to provide a simple, cross-platform interface so your browser or desktop wallet can perform actions like retrieving public addresses, signing transactions, and reading device status — without exposing keys or allowing direct arbitrary access to the hardware.

Why is Bridge necessary?

Modern browsers limit direct access to USB devices for security reasons. While protocols like WebUSB can sometimes be used, a dedicated background application avoids compatibility problems and lets Trezor provide a consistent, audited integration layer. Bridge ensures:

• Reliable cross-platform USB support (Windows, macOS, Linux).
• Security boundaries: the browser speaks to Bridge, and Bridge talks to the device.
• Automatic versioning and compatibility checks so wallets can detect updated firmware or required Bridge releases.

How it works — the basics

When installed, Bridge runs as a local background process that listens on localhost (a loopback HTTP endpoint). A web wallet detects Bridge by trying to contact the local endpoint; once confirmed, the wallet uses a defined API to request device actions. Importantly, private keys never leave the Trezor device; Bridge simply forwards commands and returns signed responses.

Typical flow:

1. User opens a compatible web wallet (e.g., Trezor Suite or other third-party wallet).
2. Wallet queries the Bridge endpoint on localhost.
3. Bridge enumerates available Trezor devices and forwards commands.
4. Trezor prompts the user on-device to confirm actions (PIN/Passphrase/confirmation).
5. Device returns signatures or requested data via Bridge to the wallet.

Security and best practices

Bridge is designed to minimize risk, but secure usage depends on the full stack: device firmware, the Bridge binary, and the wallet you use.

• Always download Bridge from the official source. Installing from third-party mirrors increases risk.
• Keep firmware up to date. Device firmware updates include security fixes and improvements.
• Verify wallet integrity. Use wallets that are well-known and open source where possible; check signatures when provided.
• Confirm actions on the device. Never approve transactions without verifying recipient addresses and amounts on the hardware screen.
• Use a strong PIN/Passphrase. Device-based authentication greatly reduces the risk of unauthorized access if your host machine is compromised.

Troubleshooting common issues

If your browser can't detect the device:

• Confirm Bridge is installed and running (check system tray or process list).
• Try a different USB cable or port — data-capable cables are required.
• Disable conflicting software that claims exclusive USB access (some virtualization or security tools).
• Restart the bridge service and the browser; clear cache if necessary.

Many wallets also expose diagnostic logs to help identify whether the error is on the Bridge, device, or wallet side.

Developer notes (brief)

For developers integrating with Bridge, the common pattern is to implement an API client that talks to the local endpoint and handles device enumeration, message framing, and user prompts. Respect device confirmation flow and never bypass on-device verification — maintaining that trust boundary is essential to user security.

When designing UI: show clear transaction details, explain required device confirmations, and surface errors from Bridge in a user-friendly way.