HotShot: Fast finality for L2s

HotShot is the BFT consensus protocol employed by Espresso. The results of the L2 sequencing marketplace, as well as blocks built by L2 sequencers, are processed by HotShot consensus and finalized within a few seconds. By sharing the same fast finality layer, L2s have certainty within seconds about what state will eventually be finalized on the L1. This is achieved by preventing sequencers from changing a transaction sequence after it has been posted and marked final by HotShot, which can happen within only a few seconds (long before settlement on Ethereum).

Compared to relying on a disparate set of centralized sequencers for soft-confirmations, sharing a decentralized consensus protocol as a finality layer bolsters the L2 ecosystem as a whole against equivocation of soft-confirmations that may occur as a result of hacks or bad actors. Applications that interact between multiple chains, such as bridges, are especially sensitive to the finality guarantees of individual chains they are involved with.

This is reflected by the fact that for many of the largest bridge providers today, the waiting time for moving funds away from a rollup is around 15 minutes; the time it takes for the bridging transaction to be finalized inside a blob or as calldata on Ethereum. With HotShot, bridging between rollups can be done in a manner of seconds, as opposed to waiting 15 minutes for transactions to finalize on the Ethereum L1, with similar security guarantees.

The finality guarantees of HotShot mirror that of Eth L1. Once HotShot finality is reached, an adversary would need to control at least 1/3rd of the overall stake to break safety. Combined with restaking, this means that HotShot's safety guarantee can approach that of Ethereum L1 over time. In the event that safety is broken, the adversary's stake will be slashed, making it very expensive to undo finality in HotShot.

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