Witnessing is an important part of any transparent ecosystem, as it ensures that misbehavior on the part of logs can be prevented or detected. This is done by ensuring that the checkpoints published by logs are consistent, which means the log is presenting the same version of its contents to everyone and thus isn't carrying out a split-view attack.
In terms of checkpoints, we consider witness implementations that use the format defined in this repository.
In terms of checking consistency, witnesses can do so in the following two (non-exhaustive) ways:
- Getting a consistency proof as defined in RFC 6962, assuming all they have is a log root.
- Getting a compact range, assuming they maintain a compact range covering the log up to the point at which they've already ensured its consistency.
We consider an interface for a witness defined as follows:
GetCheckpoint(logID): returns a checkpoint for this log, co-signed by the witness. Ideally, but not necessarily, this is the latest checkpoint.Update(logID, chkpt, pf): checks the signature in the checkpoint and verifies its consistency with its latest checkpoint from this log signer according to the proof. If all checks pass then add the checkpoint to the list maintained for this log. If the witness has no previous checkpoint for this log then this checkpoint is considered trust-on-first-use. Either way, the witness returns the latest checkpoint it has stored for this log.
This directory contains witness implementations that provide the interface defined above. Currently it contains implementations in the following languages:
- Go This can either be run as a standalone application or integrated into a larger one (for example an entity that might want to do other, application-specific checks). This witness supports both methods of checking consistency.
- Solidity This can be deployed as a smart contract on the Ethereum blockchain. There are two main contracts, each of which supports one of the consistency checks described above.