Threat model
At a high level, the bridge assumes adversaries include remote attackers, malicious websites, and compromised user systems. The primary protection is to keep private keys on the hardware device and require on-device human confirmation for any signing or sensitive operation. The bridge minimizes privileges and reduces the scope of what can be attacked.
Design constraints
Designers favor small, auditable codebases over broad feature sets. This reduces the attack surface and makes code review feasible. The bridge intentionally avoids storing secrets, erasing the need for secure key storage on the host and simplifying the threat landscape.
Communication patterns
Communication uses low-level HID/USB interactions translated into concise messages forwarded to the hardware device. Each message contains exactly what is needed for the device to render a human-readable confirmation. The bridge rejects malformed requests and enforces a strict schema for messages it forwards.
Update & signature verification
Secure distribution relies on code signing and signed installers. For firmware and bridge updates, signature verification prevents tampering. Administrators should use centralized update systems in enterprise contexts and encourage users to verify fingerprints when possible.
Operational guidance
Use minimal logging, segregate test and production environments, and require users to inspect device confirmations carefully. For high-value operations, use multi-device confirmations to split trust across independent hardware units.