You need a concept of a timestamp of a message on a stream relative to some other stream of data.
This is a distributed computing problem.
To solve this for Intercoin, we invented the Permissionless Timestamping Network
https://intercoin.org/technical.pdf
Look for descriptions of PTN. That's what you REALLY need for revocations.
The problem of revocations is then really reduced to a search and incentive problem.
You need a concept of a timestamp of a message on a stream relative to some other stream of data.
This is a distributed computing problem.
To solve this for Intercoin, we invented the Permissionless Timestamping Network
https://intercoin.org/technical.pdf
Look for descriptions of PTN. That's what you REALLY need for revocations.
The problem of revocations is then really reduced to a search and incentive problem.