Casper the Friendly Finality Gadget

Casper the Friendly Finality Gadget (FFG) proposes a hybrid mechanism to transition Ethereum from a Proof-of-Work consensus model toward Proof-of-Stake. The core contribution is a finality gadget that operates atop an existing consensus mechanism, allowing the network to achieve objective finality through a series of checkpoints. Casper FFG defines 'checkpoints' within the blockchain structure; once a supermajority of validators signs off on two checkpoints, the state is considered finalized. This provides a clear, economic guarantee that a block cannot be reverted without a significant loss of capital by the validators. The paper details the mechanism for validator deposits, the incentive structure for participation, and the slashing conditions that penalize malicious behavior such as double-voting or surround-voting. By decoupling the gadget from the underlying block production mechanism, Casper FFG offers a modular approach to securing chains. This research represents a cornerstone of the 'Ethereum 2.0' roadmap, establishing the foundation for how PoS networks manage block finality and economic security through cryptoeconomic incentives.