Vitalik Buterin, co-founder of Ethereum, stated that the network can occasionally lose finality without jeopardizing its security, despite a recent bug that nearly affected its confirmation process.
In a recent X post, Buterin mentioned that experiencing “nothing wrong with losing finalization once in a while” is acceptable. He explained that finalization signifies the network’s confidence that a block won’t be reverted.
He expressed that if there’s a significant bug causing delays in finality for hours, “that’s fine” as the blockchain remains operational during such instances. The critical concern, he noted, is “finalizing the wrong thing.”
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Experts weigh in on finalization loss
Dr. Fabrizio Romano Genovese, a computer science expert at the University of Oxford and partner at the blockchain research firm 20squares, concurred with Buterin.
He indicated that when finality is lost, Ethereum resembles Bitcoin (BTC) more closely, noting that Bitcoin has “no finality since 2009 and no one complains.”
As a proof-of-work blockchain, Bitcoin can fork into multiple chains, with the one that garners the most computational work deemed valid. However, if a secondary chain grows large enough to surpass the primary one, it invalidates the main chain and its transactions through a reorganization.
This framework leads to Bitcoin’s probabilistic finality rather than deterministic, as while it’s nearly impossible after sufficient blocks are added, reorganizations can still theoretically occur. Genovese elaborated on Ethereum’s distinct approach, where blocks are set as “final.” He explained:
“Ethereum has a finalization mechanism: When a block receives more than 66% of validator votes, it becomes ‘justified.’ If over two epochs (64 blocks) pass, the block is then finalized.”
This isn’t merely theoretical; it happened in May 2023 due to an incident akin to the recent Prysm client issue. Genovese argued that such events do not compromise the chain’s security; instead, “it just means that our guarantees around reorg have temporarily reverted to probabilistic and not deterministic.”
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Consequences for L2s and bridges
Still, Genovese emphasized that a lack of finality could impact infrastructure dependent on it, including certain inter-blockchain or layer-2 (L2) bridges.
A representative from the Ethereum sidechain Polygon informed Cointelegraph that operations would proceed as usual, but transfers from Ethereum to the sidechain “may be delayed while waiting for finality.”
Moreover, the Polygon spokesperson noted that the crosschain settlement layer AggLayer would postpone transactions from Ethereum to L2 until finality is restored. They clarified, though, that “there is no scenario in which users experience a rollback or message invalidation” due to finality loss:
“The practical impact of a delayed finality event is simply that deposits may take longer to appear. Users are not exposed to reorg-driven reversions beyond this delay.”
Genovese attributed such delays to developers who seek finality. “If a bridge builder opts not to implement fallback mechanisms during a loss of finality, that’s their choice,” he concluded.
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