key-transparency-auditor

A reference implementation of a third-party auditor for Signal's key transparency service, based on the key transparency specification.

Overview

This service is written in Java using the Micronaut framework. To build and unit test, run

./mvnw clean test

in the root directory.

The main class is the Auditor, which runs a scheduled job that requests a stream of updates from the key transparency service. It maintains a condensed view of the key transparency service's prefix tree and log tree, storing just enough information to verify and accept each update sequentially. If the auditor has processed a certain number of updates or a certain amount of time has elapsed, the auditor sends back a signed tree head to the key transparency service, indicating that its view of the prefix and log trees up to the given update matches. If the remote call succeeds, the auditor writes its state data to an AuditorStateRepository, which it may use to resume from its most recent position in the key transparency log if the auditor is restarted.

If the auditor encounters an inconsistency in verifying an update, it throws an InvalidProofException and stops sending signed tree heads back to the key transparency service.

Configuration

The service needs Auditor, KeyTransparencyServiceClient, and AuditorStateRepository beans to run. The table below describes the configuration properties necessary to instantiate those beans.