Made with GrigoraProtocol Reference · Trezor Bridge Core Specification v2.0.32
Trezor Bridge functions as the indispensable, lightweight communication daemon engineered by SatoshiLabs. Operating unobtrusively within user background processes, it establishes an encrypted HTTP-based transport layer mediating transactions, signature challenges, and serialization events between desktop browsers or client-side web interfaces and physical Trezor hardware authentication modules.
Modern web browser architectures strictly enforce sandbox boundaries that prevent websites from accessing USB hardware endpoints directly via traditional operating system APIs without explicit protocol abstraction. Historically, browser plugins like NPAPI permitted this direct interaction; however, the retirement of legacy plugin architectures demanded a dedicated, memory-safe middleware. Trezor Bridge fulfills this fundamental role by initiating an independent local loopback service listening exclusively on designated ports 21325 and 21324.
Rather than exposing raw USB pipes directly to browser scripts, Trezor Bridge translates high-level cryptographic commands encoded in Protocol Buffers (protobuf) into sanitized, low-level USB human interface device (HID) and WinUSB packets. This ensures all interaction requests from decentralized applications, web wallets, and management interfaces undergo strict format verification before ever reaching the physical hardware microcontroller. The architecture deliberately contains no private keys, seed phrases, or sensitive wallet state, operating solely as an ephemeral, stateless message transport pipeline.
Trezor Bridge has been engineered for minimal memory overhead and zero active CPU consumption during idle states. It runs natively across major desktop environments with no external runtime dependencies like Java or Python.
Windows 10/11 (64-bit), macOS 10.15 Catalina or later (native Apple Silicon and Intel support), and standard Linux distributions (Ubuntu, Fedora, Debian via DEB/RPM/udev rules).
Chromium family (Google Chrome, Brave, Microsoft Edge, Opera), Mozilla Firefox, and Chromium-based Web3 interfaces with localhost cross-origin resource sharing permissions enabled.
Standard USB 2.0 or USB 3.0 Type-A/Type-C ports providing minimum 500mA output. USB hubs must be powered to avoid packet drops during cryptographic signing cycles.
1
Download the verified installer directly from the official SatoshiLabs repository or prompt page. Always inspect the SSL certificate on the download domain to preclude man-in-the-middle substitutions. Do not download Bridge binaries from unverified third-party web aggregators.
2
Launch the executable package (.exe on Windows, .pkg on macOS, or package manager on Linux). Windows UAC prompts and macOS security dialogs will request elevated permissions to deploy the background service daemon and bundle standard USB drivers into the system tree.
3
For Linux workstations, register the SatoshiLabs vendor ID inside /etc/udev/rules.d/51-trezor.rules. Trigger rule reloading using sudo udevadm control --reload-rules followed by sudo udevadm trigger to allow non-root users direct communication access with the USB device nodes.
4
Upon completing setup, the bridge launches invisibly as trezord. Check active operation by opening your web browser and navigating to http://127.0.0.1:21325/status/. A valid installation immediately renders a clean diagnostic payload reporting the compiled version string and connected bus enumeration.
Once the physical device (Trezor Model One, Model T, or Trezor Safe 3) is connected via a data-capable cable, the operating system assigns a USB device descriptor. Trezor Bridge continuously polls the local bus for vendor IDs (0x534c for SatoshiLabs or 0x1209). When detected, Bridge initializes an open session lock, preventing competing software instances from sending conflicting commands. The web application issues an Initialize call, retrieving the device's public features, firmware version, and device ID, all while sensitive private cryptographic keys remain permanently isolated behind physical hardware memory safeguards.
If web interfaces indicate 'Device Not Detected' or 'Bridge Unavailable', run systematically through the following diagnostic procedures to identify and isolate transport faults:
Many cheap USB cords only possess power conductors without data transmission lines. Swap cables and connect straight to the workstation motherboard, bypassing passive unpowered multiport adapters.
Inspect Task Manager (Windows) or Activity Monitor (macOS) for the process labeled 'trezord'. If stopped, manually start the service via system services or execute 'sudo systemctl restart trezord' on Linux.
Aggressive third-party antivirus suites and ad-blockers sometimes intercept inbound localhost requests to port 21325. Whitelist 127.0.0.1 or disable blocking extensions to restore seamless CORS handshakes.
Security remains the cornerstone of Trezor's design philosophy. Trezor Bridge enforces strict Cross-Origin Resource Sharing (CORS) header verification to disallow arbitrary web origins from issuing unauthorized device polling commands. Crucially, Trezor Bridge operates entirely within a zero-trust model regarding host memory: it cannot read or parse secret data because the recovery seed, private keys, and deterministic derivation logic never exit the secure element or microchip boundaries of the Trezor hardware.
Every critical transaction payload, address verification prompt, or cryptographic signature request transported via Bridge requires physical, human confirmation on the device screen itself. Even in scenarios where a host computer is compromised by keyloggers or malicious remote access tools, Bridge can only relay unsigned payloads to the physical unit. The transaction cannot be executed without explicit tactile confirmation on the device's physical buttons or touchscreen.
Query local port 21325 to inspect active bridge headers and connection counters.