The witness is an HTTP service that stores STHs it has seen from a configurable list of Certificate Transparency logs in a sqlite database. This is a lightweight way to help detect or even prevent split-view attacks. An overview of witnessing can be found in trillian-examples, along with "generic" witness implementations. This witness is designed to be compatible with the specific formats used by CT.
Once up and running, the witness provides three API endpoints (as defined in api/http.go):
/ctwitness/v0/logsreturns a list of all logs for which the witness is currently storing an STH./ctwitness/v0/logs/<logid>/updateacts to update the STH stored forlogid./ctwitness/v0/logs/<logid>/sthreturns the latest STH forlogid.
Running the witness is as simple as running go run ./cmd/witness/main.go from
this directory, with the following flags:
listen, which specifies the address and port to listen on.db_file, which specifies the desired location of the sqlite database. The use of sqlite limits the scalability and reliability of the witness (because this is a local file), so if that is required a different database backend would be needed.config_file, which specifies configuration information for the logs. This repository contains a sample configuration file, and in general it is necessary to specify the following fields for each log:logID, which is the alphanumeric identifier for the log.pubKey, which is the base64-encoded public key of the log. Both of these fields should be populated using an "official" CT log list.
private_key, which specifies the private signing key of the witness. In its current state the witness does not sign STHs so this can exist in any form.