In the cryptoworld, Casper is an umbrella term that covers two fundamental upgrades for Ethereum. The first one is called “Casper the Friendly Finality Gadget” (FFG). This consists in a change from the current pure Proof of Work (PoW) validation system to a hybrid form of Proof of Stake (PoS) and PoW. It is planned to be implemented throughout 2018 and the beginning of 2019. The second upgrade is called “Casper the Friendly GHOST: Correct by Construction” (CBC). This is a full PoS blockchain fork-choice rule protocol. Its implementation is planned for the coming years. In the following article, we concentrate on explaining Casper FFG. We chose only this upgrade because it will be implemented sooner and it is more relevant for Pool of Stake. Please do not be intimidated by the terminology. this article is intended to paint a simple and clear picture of Casper FFG. However, we do expect the reader to be at least familiar with PoW, PoS, and their main differences.
What sets Casper FFG apart from most other PoS algorithms, is that there is a process to punish malicious behavior. As we stated before, validators will lock up a portion of their ETH in a similar condition to staking a bet. Any malicious behavior makes the validator lose this bet. Casper FFG is designed to be “Byzantine Fault Tolerant”. This means that it punishes any act that has a malicious (or Byzantine) intent. Casper FFG’s behavior control does not stop here. It has additional controls to guarantee network security, including punishing validators that go offline. The idea is to not only reward good behaviour (as other PoS) but also punish malicious behaviour. This creates an additional incentive (or fear of punishment) for validators, who need to make sure that they take care of their node uptime.
Casper FFG is designed to ease the initial transition to PoS. This is going to be done by overlaying a smart contract over the normal “ethash” PoW protocol currently in use. Miners will continue to create new blocks and every 50th block a PoS mechanism will be used. This will ensure that every 50th block “finality” is reached. “Finality” refers to a record of a transaction or operation that is forever registered in a ledger and cannot be reverted. It is argued that no system can provide 100% finality, but Casper FFG comes quite close. There are three reasons where Casper FFG does this very well.
In conclusion, Casper FFG provides a set of reasons to get close to finality, and benefits to the Ethereum network. The punishing mechanism that derives from the ⅔ based agreement system creates a huge deterrent for attackers, since any malicious activity would result in a harsh penalty. Additionally, it would also lead to a depreciation of the token that the malicious actor holds. Apart from this, the benefits that Casper FFG will bring to Ethereum include higher decentralization, energy efficiency, economic security, and the ability to scale.
source
https://www.poolofstake.io/blog/casper-ethereums-treasure-keeper/