This deck explains the purpose, architecture, and security model of Trezor Bridge: the browser-to-hardware helper used to enable secure communication between desktop clients and a Trezor hardware wallet. It covers connection flow, authentication, threat models, implementation guidance, and best practices for maintaining device integrity and user privacy.
Desktop browsers historically limited direct USB access for security reasons. Trezor Bridge runs as a local native helper that safely exposes a controlled API over an HTTP endpoint on localhost so that web-based wallet interfaces can talk to the hardware device. This avoids browser extension risks and reduces the attack surface while preserving user convenience.
Bridge is built around minimal trusted code, least-privilege interfaces, clear user consent, and transparent updates. These principles reduce the risk of unauthorized device actions and keep cryptographic secrets on the hardware device.
Key components include the hardware device, the Trezor Bridge native service, the browser-based wallet app, and the host OS. Communication path: Browser → HTTPS (localhost) → Bridge → USB → Trezor. Bridge translates HTTP JSON-RPC requests into raw HID/USB commands and presents structured responses back to the web UI.
Connection starts with the wallet discovering Bridge on a localhost port, requesting a session, and then issuing user-approved commands (e.g., get public keys, sign transaction). The device requires physical confirmation for sensitive operations.
Trezor’s security model assumes the host may be compromised. The core promise is that private keys never leave the device and every critical operation requires an on-device confirmation by the user. Bridge enforces origin checks, CORS rules, and limits which endpoints are accessible.
Bridge implements explicit pairing and origin verification: the wallet app identifies itself, and the device displays transaction metadata to the user for approval. This prevents remote sites from issuing hidden requests without user knowledge.
Bridge typically uses JSON-RPC over HTTP on localhost. Payloads are concise: commands, parameters, and binary responses encoded as base64 when necessary. Timeouts and size limits are present to mitigate resource abuse.
Errors are explicit and structured to help wallets present human-friendly messages. Examples include device disconnected, user rejected, malformed request, or firmware incompatibility.
Malware on the user’s computer can try to spoof Bridge endpoints or intercept communication. Bridge combats this with well-known localhost ports, signed installers, a unique TLS fingerprint for localhost, and checks that pair the browser origin with the device session.
Wallet interfaces must show clear transaction details and request on-device approval to prevent phishing sites from tricking users into signing malicious transactions. Users should verify addresses and amounts on the device screen.
Bridge is distributed as signed installers for major OSes. Automatic update checks are cryptographically verified. Organizations may prefer signed packages from official repositories and network policies to limit deprecated versions.
When building web wallet apps, follow origin-based access controls, handle errors gracefully, and never assume the device is always available. Use exponential backoff for retries and inform the user when physical interaction is required.
Include tests for device disconnect, permission denial, malformed responses, and firmware mismatch. Use testnets for transaction flows and ensure logs do not leak sensitive payloads.
Only install Bridge from official channels, keep firmware up to date, never enter your recovery seed into a computer, and always confirm transaction details on the device screen. Treat the recovery seed as the single point of failure and store it offline.
Trezor Bridge acts as a narrow, auditable bridge between web wallets and the hardware device. Its primary role is to preserve the security properties of the hardware—keeping private keys isolated while enabling a modern web UX. By combining strict device confirmation, signed releases, and careful client design, Bridge minimizes risk while maximizing compatibility.
Official resources and downloads: Trezor official • Open in PowerPoint Online