Casper FFG

A proof-of-stake consensus protocol combined with LMD-GHOST to determine the head of the Ethereum Beacon Chain.

What is Casper FFG?

Casper the Friendly Finality Gadget (FFG) is a proof-of-stake (PoS) consensus mechanism designed to enhance the security and finality of blockchain networks, specifically integrated into Ethereum’s Beacon Chain. It works in tandem with the LMD-GHOST (Latest Message Driven - Greediest Heaviest Observed SubTree) fork choice rule to enable consensus clients to agree on the canonical chain head. Casper FFG introduces a hybrid approach that combines PoS with elements of finality, ensuring that blocks are finalized periodically, reducing the risk of chain reorganizations.

In Casper FFG, validators stake ETH to participate in block proposal and attestation processes. The protocol operates through checkpoints (specific blocks at regular intervals) where validators vote to finalize a chain segment. Once a checkpoint achieves supermajority votes (two-thirds of validators), it becomes “justified” and, after further confirmation, “finalized,” making it highly unlikely to be reversed. This finality mechanism provides stronger guarantees of transaction permanence compared to proof-of-work systems. Casper FFG was a critical component in Ethereum’s transition from proof-of-work to proof-of-stake during the Merge in September 2022, ensuring efficient and secure consensus on the Beacon Chain.