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

Layer 2 Plasma
3

This is great—and definitely improves on the trade-offs in a Plasma context, relative to my previous suggestions.

Few questions:

  1. Perhaps you could cut down on the size of the non-existence proofs by putting a Bloom filter of the spent coins in the Plasma block header. Everyone could receive and cache the Bloom filters, and you’d only need a proof for blocks for which there’s a false positive for your coin. I’m not that familiar with probabilistic data structures but I wonder if there’s a way to parametrize it so that the shared data is pretty small but, absent misbehavior by the Plasma chain operator, false positives will happen so rarely (say 1 in a billion transactions) that withdrawal would be a sufficient remedy.
  2. I’m not sure it would work to use a ZK-snark for the non-existence proofs, unless the parent chain is willing to accept ZK-snarks for the exit transactions. Otherwise, you don’t have enough information to respond to a challenger, right?
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