Peer Review: CBC Casper

Overview of Review:

Full Technical Review:

What the CBC Casper Paper Achieves and Why You Cannot Treat Correctness Without Liveness

  1. Nodes in such a system will share common future protocol states (in the face of a fault-tolerance level t)
  2. Subsequent decisions will be consistent (because they share future protocol states)
  3. This leads to fault tolerance.

Liveness Imposes Stricter Fault Thresholds than Safety

  • The consensus values are {0, 1}
  • W(v) = 1 for all v.
  • The protocol states encode the sequences of authenticated messages each validator received from each other validator (let us assume for now that messages cannot be forged, replayed, or arbitrarily delayed).
  • The estimator function looks at a validator’s protocol state and decides whether or not a consensus value was agreed upon by a BFT quorum of validators in V (i.e. at least 2f + 1 votes agree on the same property for a consensus value).
  • The useful consensus value property that requires an argument of liveness is “all correct validators decide c”, where c is a consensus value.
  • t <= T_s <= 1/3 * sum(W(v)) < sum(W(v))
  • t <= T_l <= 1/2 * sum(W(v)) < sum(W(v))

Conclusion

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