Casper the Friendly Finality Gadget (FFG) will be the first major Casper protocol development initiative to launch on the mainnet. FFG is a proof-of-work/proof-of-stake hybrid iteration of Casper intended to gradually move the Ethereum network away from PoW mining.
FFG is mostly a regular proof-of-work, except that for every 50 blocks there is a vote among Ethereum staking nodes termed “finality”. FFG is currently running on the Ethereum testnet and will be pushed out onto the mainnet as part of Constantinople hard fork sometime in late 2018. Casper Correct By Construction (CBC) is the second major Casper protocol development initiative, with a launch on the Ethereum mainnet planned for sometime in 2019.
FFG, aka “Vitalik’s Casper” (Ethereum creator Vitalik Buterin is FFG’s project lead), provides assurance and finality to the underlying blockchain with a gradual “step-wise approach” transition from PoW to PoS. FFG’s smart contract configuration is layered on top of the existing PoW network.
Buterin wrote in October 2017, upon first publishing his ideas for Casper FFG, “Within Ethereum, the proposal mechanism will initially be the existing proof of work chain, making the first version of Casper a hybrid PoW/PoS system. In future versions, the PoW proposal mechanism will be replaced with something more efficient. For example, we can imagine converting the block proposal into some kind of PoS round-robin block signing scheme.”
The Casper FFG blockchain will grow every block with the existing ethash PoW algorithm, then “pause” after every 50 blocks to let ethstakers validate and establish finality consensus on the 50th block. The 50 block period is an “Epoch” and the vote on the 50th block is a “checkpoint”. PoW miners mine blocks and PoS validators validate checkpoints at the end of every epoch. When two consecutive epochs achieve 2/3+ votes-by-weight, the first of these epochs is “finalized”.
Ethereum’s governing protocol will vet how well FFG performs on top of existing PoW architecture. When FFG is deemed a success, Ethereum will move on to implementation of Correct By Construction.