Part 2: Technical Overview
Here's the opening sentence of a paper about attacks on the Ethereum 2.0 consensus protocol:
The Proof-of-Stake (PoS) Ethereum consensus protocol is constructed by applying the finality gadget Casper FFG on top of the fork choice rule LMD GHOST, a flavor of the Greedy Heaviest-Observed Sub-Tree (GHOST) rule which considers only each participant's most recent vote (Latest Message Driven, LMD).
If that makes perfect sense to you then feel free to skip this chapter entirely. Otherwise, read on!
Our aim is to understand that sentence in all its parts. There's a lot to unpack, but we'll take time over it. We'll begin with some preliminaries covering basics of consensus that are not particularly specific to Ethereum.
After a high-level overview of the how the whole consensus protocol fits together, we will dive down into its component parts, first LMD GHOST, then Casper FFG. In the Gasper section we will see how these two are combined together.
Enough subtleties and edge cases arise from the way that the LMD GHOST and Casper FFG protocols interoperate that I've dedicated the closing section of this chapter to discussing these issues.