Verifiable Light-Weight Monitoring for Certificate Transparency Logs
This addresses security and trust issues for entities relying on CT monitoring services, though it is incremental as it builds on existing CT infrastructure.
The paper tackles the problem of trust in Certificate Transparency (CT) monitoring services by introducing a CT/bis extension for verifiable light-weight monitoring, enabling subjects to verify notification correctness and reducing reliance on trusted monitors.
Trust in publicly verifiable Certificate Transparency (CT) logs is reduced through cryptography, gossip, auditing, and monitoring. The role of a monitor is to observe each and every log entry, looking for suspicious certificates that interest the entity running the monitor. While anyone can run a monitor, it requires continuous operation and copies of the logs to be inspected. This has lead to the emergence of monitoring-as-a-service: a trusted party runs the monitor and provides registered subjects with selective certificate notifications, e.g., "notify me of all foo.com certificates". We present a CT/bis extension for verifiable light-weight monitoring that enables subjects to verify the correctness of such notifications, reducing the trust that is placed in these monitors. Our extension supports verifiable monitoring of wild-card domains and piggybacks on CT's existing gossip-audit security model.