  Ethereum's current Gasper consensus mechanism, which combines the Latest
Message Driven Greediest Heaviest Observed SubTree (LMD-GHOST) fork choice rule
with the probabilistic Casper the Friendly Finality Gadget (FFG) finality
overlay, finalizes transactions in 64 to 95 blocks, an approximate 15-minute
delay. This finalization latency impacts user experience and exposes the
network to short-term chain reorganization risks, potentially enabling
transaction censorship or frontrunning by validators without severe penalties.
As the ecosystem pursues a rollup-centric roadmap to scale Ethereum into a
secure global settlement layer, faster finality allows cross-layer and
inter-rollup communication with greater immediacy, reducing capital
inefficiencies. Single slot finality (SSF), wherein transactions are finalized
within the same slot they are proposed, promises to advance the Ethereum
protocol and enable better user experiences by enabling near-instant economic
finality. This thesis systematically studies distributed consensus protocols
through propose-vote-merge, PBFT-inspired, and graded agreement families -
scrutinizing their capacities to enhance or replace LMD-GHOST. The analysis
delves into the intricate tradeoffs between safety, liveness, and finality,
shedding light on the challenges and opportunities in designing an optimal
consensus protocol for Ethereum. It also explores different design decisions
and mechanisms by which single slot or fast finality can be enabled, including
cumulative finality, subsampling, and application-layer fast finality.
Furthermore, this work introduces SSF-enabled and streamlined fast finality
constructions based on a single-vote total order broadcast protocol. The
insights and recommendations in this thesis provide a solid foundation for the
Ethereum community to make informed decisions regarding the future direction of
the protocol's consensus.
