params: drop evidence.MaxAgeNumBlocks in the next major release

[melekes]

After PBTS is enabled by default for all chains, we should be able to remove evidence.MaxAgeNumBlocks (see tendermint/tendermint#2653 (comment)). That's because a timewarp attack (+1/3 cabal modifying block's time) will no longer be possible.

[andynog]

My understanding is that PBTS will not be enabled by default.

If enable is not enforced then I believe you might still need to keep evidence.MaxAgeNumBlocks around, or do a big refactoring of the evidence codebase logic to check if PBTS is enabled or disabled (or when it will be enabled) and then use MaxAgeNumBlocks in the logic or not.

But since PBTS can be enabled for a future height via FeatureParams.PbtsEnableHeight I guess this just complicates the logic for evidence validation.

[cason]

But block times can still be arbitrarily long, due to failures, asynchrony, etc.

So we probably still need to have the requirement of both time interval ("real" time) and blocks committed ("logic" time).

[melekes]

But block times can still be arbitrarily long, due to failures, asynchrony, etc.

So we probably still need to have the requirement of both time interval ("real" time) and blocks committed ("logic" time).

You mean 1/3+ cabal will still be able to delay block commit for arbitrary time. Therefore we still need MaxAgeNumBlocks?