What is Trezor Bridge?
Trezor Bridge is a crucial, open-source application that runs on your computer, acting as a communication "bridge" between your Trezor hardware wallet and web-based applications like the Trezor Wallet. In simple terms, web browsers, for security reasons, cannot directly access your computer's USB ports to talk to hardware devices. Trezor Bridge solves this problem by running as a small, local background service.
When you access a compatible web wallet, the browser sends a request to this local service, which then "bridges" that request to your physically connected Trezor device. It securely fetches the necessary information (like your public keys) or passes along transaction data for you to sign. Most importantly, your private keys never, ever leave the Trezor device. The Bridge only facilitates the flow of *unsigned* and *signed* data, not the keys themselves.
Think of it as a secure translator and messenger. Your browser speaks "web," and your Trezor speaks "USB." Trezor Bridge sits in the middle, translating their messages and ensuring they can communicate securely without either one having to learn the other's language or, critically, without the browser ever gaining access to the sensitive hardware.
Background: Why Do We Need a Bridge?
The concept of Trezor Bridge emerged from a fundamental security principle of web browsers: the "sandbox." A website you visit should be isolated from your computer's operating system and hardware. It shouldn't be able to read your local files, access your webcam without permission, or communicate with random USB devices. This sandbox is what keeps you safe from malicious websites.
However, this creates a challenge for hardware wallets. A hardware wallet's entire purpose is to connect to your computer via USB, and you need to interact with it using a user-friendly interface—often, a web-based wallet. This presented a paradox: how do you allow a web page to talk to a specific, user-approved USB device without punching a giant, insecure hole in the browser sandbox?
In the early days of cryptocurrency hardware wallets, the common solution was to use browser plugins or extensions. Users would install a plugin that had elevated permissions to access USB devices. The web wallet would then talk to the plugin, which in turn would talk to the hardware. This approach, however, proved problematic. Browser plugins became a massive target for hackers. Malicious plugins could be created to mimic official ones, phishing for user credentials or even attempting to manipulate transaction data. Furthermore, plugin architectures were complex and varied between browsers like Chrome, Firefox, and Safari, making development and maintenance a nightmare.
SatoshiLabs, the creators of Trezor, recognized these risks and limitations. They needed a solution that was more secure, more reliable, and browser-agnostic. The answer was Trezor Bridge. By creating a standalone application that the user installs *once* on their operating system (Windows, macOS, Linux), they moved the hardware communication logic *out* of the browser and into a trusted, locally-running program. This program, `trezord`, is digitally signed and open-source, allowing anyone to verify its code and confirm its safety.
How It Works: A Look Under the Hood
Trezor Bridge's operation is both clever and straightforward. When you install it, it sets up a tiny web server that runs only on your own computer, a concept known as "localhost." This server is not accessible from the internet; it only listens for requests originating from your own machine.
The process looks like this:
- 1. User Action: You plug in your Trezor and visit the Trezor Wallet website in your browser (e.g., Chrome, Firefox).
- 2. Browser Request: The web wallet's code, running in your browser, needs to find your Trezor. It sends an HTTP request not to an external server, but to a specific address on your local machine: `http://localhost:21325`.
- 3. Bridge Receives: The Trezor Bridge application, which is constantly listening on that "port" (21325), receives this request.
- 4. USB Communication: The Bridge translates the web request into a low-level USB command and sends it to your connected Trezor device.
- 5. Device Responds: Your Trezor receives the command (e.g., "What are your public keys?"), processes it, and sends a response back via USB.
- 6. Bridge Returns: The Bridge takes the USB response, packages it into a web-friendly format (JSON), and sends it back to the browser as the reply to its original `localhost` request.
- 7. Wallet Updates: The web wallet receives this data and updates the interface, perhaps showing you your account balance.
When you create a transaction, the same process happens. The web wallet sends the *unsigned* transaction details to the Bridge, which passes them to the Trezor. Your Trezor device then displays the details on its screen, asking you to physically confirm. Once you press the button, the device *signs* the transaction internally using your private key. It then passes the *signed* transaction (which is safe to share) back to the Bridge, which gives it to the browser to be broadcast to the network. Your private key never, for even a millisecond, exists outside your Trezor's secure chip.
Feature Spotlight: Trezor Bridge vs. WebUSB
While Trezor Bridge is the classic, rock-solid solution, a newer technology called WebUSB has also emerged. WebUSB is a modern web standard that allows browsers (with your explicit permission) to communicate directly with USB devices, effectively making a "bridge" unnecessary. The Trezor Model T was designed to support WebUSB, while the Trezor One relies on the Bridge. Here's how they compare:
| Feature | Trezor Bridge | WebUSB |
|---|---|---|
| Setup Requirement | Requires a one-time software installation on the user's computer. | No software installation needed. Works "out of the box" in the browser. |
| Browser Compatibility | Works with all major browsers (Chrome, Firefox, Safari, Edge) because it uses standard web requests. | Only supported by Chromium-based browsers (Chrome, Opera, Edge). Notably, Firefox and Safari do not support it. |
| Communication Model | Browser ➔ Localhost Server ➔ USB Device | Browser ➔ USB Device (Directly, after user permission) |
| Security Model | Relies on a locally installed, open-source, and digitally signed application. Communication is isolated to the local machine. | Relies on the browser's built-in security model, which prompts the user to manually select and approve a specific device. |
| Primary Trezor Device | Trezor Model One (Required). Also acts as a fallback for Model T. | Trezor Model T (Primary method). Not supported by Trezor Model One. |
Frequently Asked Questions (FAQs)
1. Is it safe to install Trezor Bridge on my computer?
Yes, it is extremely safe. The Trezor Bridge application is developed and digitally signed by SatoshiLabs, the official creators of Trezor. It is also fully open-source, meaning its code has been reviewed by security experts worldwide.
The Bridge does not have access to your private keys, which never leave your Trezor device. Its only job is to pass messages back and forth, and it only runs on your local machine, so it is not exposed to the internet.
2. Do I need Trezor Bridge if I have a Trezor Model T?
It depends on your browser. The Trezor Model T primarily uses WebUSB, which works automatically in browsers like Google Chrome. If you use Chrome, you likely do not need to install Trezor Bridge for your Model T to work.
However, if you use a browser that does not support WebUSB (like Firefox), you will need to install Trezor Bridge to act as the communication layer. It is generally a good idea to have it installed as a robust fallback, as it ensures your device will work across all browsers.
3. How do I know if Trezor Bridge is running?
Trezor Bridge runs as a background process. On Windows, you can typically see its icon in your system tray (near the clock). On macOS, it appears in your menu bar. On Linux, it runs as a system daemon.
The easiest way to check is to visit the Trezor Wallet website. If it connects to your device (and you are using a Trezor One, or a Model T in Firefox), the Bridge is working correctly. The Trezor Wallet interface will also show the Bridge's connection status.
4. What happens if I have both Trezor Bridge and a WebUSB-compatible browser?
The Trezor Wallet is designed to handle this gracefully. If you are using a Trezor Model T in a browser like Chrome, the wallet will default to using the "native" WebUSB connection as it's the most direct path. It will simply ignore the running Trezor Bridge. If that WebUSB connection fails for any reason, or if you are using a Trezor Model One, the wallet will then automatically try to connect via the Trezor Bridge. It's a seamless fallback system.
5. Can Trezor Bridge see my private keys or recovery seed?
Absolutely not. This is the most critical security principle of the Trezor. Your private keys and recovery seed are generated *inside* the Trezor and are physically prohibited from ever leaving the device's secure chip.
Trezor Bridge only transports *public* data (like your public addresses to check balances) and *signed transactions*. A signed transaction is cryptographically secure and does not contain your private key; it only proves that you (the key holder) approved it. The Bridge, like the browser, is "blind" to your secrets.