Luca Zanolini

Luca Zanolini

Research Scientist at the Ethereum Foundation. PhD in Computer Science.

3-Slot-Finality: SSF is not about “Single” Slot

1 minute read

Published:

In this post, we introduce 3-Slot Finality (3SF), a protocol designed to finalize blocks proposed by an honest proposer within 3 slots when network latency is bounded by a known value Δ – even if subsequent proposers might be dishonest – while requiring only one voting phase per slot. This approach contrasts with previously proposed protocols for Single-Slot Finality 14, which require three voting phases per slot to finalize an honestly proposed block within a single slot resulting in longer slot time. We also show that 3SF guarantees all the key properties expected from SSF, offering an efficient and practical alternative that reduces overhead while ensuring fast and predictable block finalization within a few slots, and a shorter practical slot time (as voting phases take practically longer than other phases). As a result, our protocol achieves a shorter expected confirmation time compared to the previously proposed protocol, at the expense of a slight delay in block finalization, which extends to the time required to propose three additional blocks, rather than finalizing before the next block proposal. However, we believe that a shorter expected confirmation time could be sufficient for most users. Also, slot time is a crucial parameter affecting economic leakage in on-chain automated market makers (AMMs) due to arbitrage. Specifically, arbitrage profits – and consequently, liquidity providers’ (LP) losses – are proportional to the square root of slot time. Therefore, reducing slot time is highly desirable for financial applications on smart contract blockchains. Finally, we show that we can make a further trade-off: we can increase the number of voting phases to two, without this affecting the actual slot length, and achieve finalization in only two slots.

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