Arbitrator is not an Alligator
The Qubic Arbitrator, unlike the IOTA Coordinator, has limited power and can be replaced if it misbehaves.
Qsilver · Jan 2, 2024.
Yes, they both start with “A” and end with “ator,” but amazingly, the Qubic arbitrator is not anything like an alligator.
Of course, it would be very silly to even think that such could be true, but some people who should do a bit of research before posting have claimed that the Qubic arbitrator is centralized like the IOTA coordinator. Notice both end with “ator,” so the false assumption can be forgiven.
Rather than rely on random internet posts, I find it much more effective to read the code and see what it says.
Role of the Arbitrator
Initially, it looked like the arbitrator could steal the 1 trillion mining reward for the epoch. However, a deeper look showed that arbitrator transactions happen without any arbitrator signature and directly update the balances of the computors according to a performance scale. Essentially, the arbitrator address gets the leftover funds (around 1% or less recently) without doing anything. The better the computors perform, the less the arbitrator receives. Over its lifetime, the arbitrator address has accumulated almost 1.5 trillion QU, about 2%, but at current rates, it will take many years to reach 2 trillion QU.
Arbitrator Functions
The arbitrator sets the 8 random bytes for the miners each epoch. This can be automated once the RANDOM SC is completed, along with the main function of publishing the list of computors for the epoch.
The arbitrator's ability to publish the list of computors for the epoch is where its real power lies. However, all computor nodes track the performance of all computors, candidates, and newcomers for each tick. This means that in a future update, the quorum itself can set the list of computors for the next epoch, with the arbitrator simply signing off if the list matches the rankings.
The arbitrator's function then becomes a rubber stamp on a deterministically determinable list of computors.
Handling Misbehavior
If the quorum-generated list of computors is not approved by the arbitrator, a QU stake-weighted election would determine which computor slate had the best performance. This would sort scores without politics. If the quorum or arbitrator is infiltrated by an attacker, it would be resolved by the Qubic stakeholders, causing at most a temporary pause before the new epoch starts. Not ideal, but not disastrous, and plans can be made to handle such events.
After the QU vote, computors would update with a new address for the arbitrator if needed. The arbitrator is replaceable and the job is straightforward. Any misconduct by the arbitrator would be quickly noticed due to the high competition and cost involved in maintaining computor spots, leading to a scandal.
Protection Mechanisms
CfB clarified that arbitrator misbehavior is already not allowed. The arbitrator tampering with the list would result in replacement within 15 seconds by setting another public key. This ability has been tested successfully.
Conclusion
Protection from an "evil" arbitrator is in place. The transaction with the list of new computors would not be included in the tick, leading to a QU stake-based election to resolve the split. While a tied election might result in a fork, this seems very unlikely. Even in such an event, we would have two versions of Qubic, similar to BCH from BTC and ETC from ETH (or ETH from ETC!).
Sources
@DesheShai @Qsilver97 @hus_qy @5onOfCrypto ”Full control for nodes not relying on internal data. Arbitrator tampering with the list will get replaced within 15 sec (it’s just setting another public key). We already tested ability to replace Arb.”
Come-from-Beyond clarified on Qubic Discord:
“Arb publishes list for newcomers and those without full nodes. Quorum relying on the list (and verifying it) shows the list is correct. Invalid list event would become known to users very soon (by seeing no tick progress).”
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