Plasma XT: Plasma Cash with much less per-user data checking

[danrobinson]

@kfichter

The nice thing about this as that the EVM doesn’t even have to “understand” what the bitmaps represent. Someone could publish a bitmap along with the string “every coin ending with 2 or 3”, and it would (theoretically) work. Of course we’d rather have some semantics that the Plasma Cash client can understand, but it shows what options we have.

I think it eventually has to—you need to prove that the recipient of the checkpointing was on notice, so in the event of a challenge, the EVM needs to be able to evaluate whether the published representation of the set being checkpointed included a particular coin.

(Another reason evaluating these needs to be computationally simple is of course that every coinholder needs to interpret every checkpoint, at least sufficiently to know that their coins are not included in it.)