LMD-GHOST
A fork choice algorithm used with Casper FFG to determine the canonical head of the Ethereum Beacon Chain.
What is LMD-GHOST?
LMD-GHOST, or Latest Message Driven - Greediest Heaviest Observed SubTree, is a fork choice rule used in Ethereum’s proof-of-stake (PoS) Beacon Chain to select the canonical chain head. It works in conjunction with the Casper FFG (Friendly Finality Gadget) consensus protocol to ensure validators agree on the valid chain in a decentralized network. LMD-GHOST is designed to handle the complexities of PoS systems, where validators attest to blocks, and the chain may experience temporary forks due to network latency or competing proposals.
The algorithm operates by evaluating the “weight” of a chain, determined by the number of validator attestations supporting each block. It prioritizes the subtree (branch) with the most recent attestations, selecting the “heaviest” branch as the canonical chain head. The “Latest Message Driven” aspect ensures that only the most recent attestation from each validator is considered, preventing older or stale votes from influencing the fork choice. LMD-GHOST’s design provides resilience against certain attacks, such as balancing attacks, and complements Casper FFG’s finality mechanism by dynamically resolving forks in real-time, ensuring Ethereum’s Beacon Chain progresses securely and efficiently.
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