AIP: BOLD - permissionless validation for Arbitrum

Proposals
70

It is important to highlight that as part of the initial BoLD 1.0.0 release, there is a Delay Buffer feature, which aims to limit the negative effects of:

  • prolonged parent chain censorship,
  • prolonged sequencer censorship, and/or unexpected
  • sequencer outages.

A potential issue arises In the event that the parent chain is being repeatedly censored or if the L2 sequencer is offline, every block level assertion and/or sub-challenge assertion would need to wait 24 hours before they can bypass the sequencer (using the theSequencerInbox’s forceInclusion method described here). If this were to happen, challenge resolution would be delayed by a time t where t = (24 hours) * number of moves for a challenge. To illustrate with sample numbers, if a challenge takes 50 sequential moves to resolve, then the delay would be 50 days.

The Delay Buffer feature mitigates this by implementing some time threshold that is decremented when unexpected delays occur. Once that time threshold is met, the force inclusion window is lowered - effectively enabling entities to make moves without the 24 hour delay-per-move.

Under reasonable parameterization, the sequencer could be offline / censoring for 24 hours twice, before the force inclusion window is effectively dropped from 24 hours to a minimum inclusion time. The force inclusion window gradually (over weeks) replenishes to it’s original value over time as long as the sequencer is on “good behavior” - regularly sequencing messages without unexpected delays.

Here are the initial parameter values, which might change slightly as there are still active discussions:

  • delay buffer B = 14400 L1 blocks (2 days)

  • threshold T = 150 L1 blocks (30 minutes)

    • well above our typical posting frequency
    • *replenish rate r = 5% meaning 1 days is replenished every 20 days, or roughly a 95% uptime

  • delayBlock D = 7200 (1 day)

We believe that the Delay Buffer feature provides stronger guarantees of censorship resistance for Arbitrum chains. As always, Orbit chain owners can change the default parameters as they see fit for their use case.

The Delay Buffer feature was not specifically elaborated on in the original temperature check which passed on Snapshot, and since it will be included in the Tally vote, we want to ensure that it is being highlighted.

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