add page on pow v pos

[jmcook1186]

Description

adds page with high level discussion of proof-of-stake vs proof-of-work

Related Issue

#8285

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[minimalsm]

I suggested we split up the 'Cost to attack' section with H4s to make it less monolithic and easier to read. Other than that, this is good to go in my eyes 🙏👍

[minimalsm]

This section is pretty long. What do you think about breaking it up with some H4s?

Suggested:

• What is an attack
• 33% attacks
• 51% attacks

Suggested change

	In proof-of-stake, validators are required to escrow ("stake") at least 32 ETH in a smart contract. Ethereum can destroy staked ether to punish validators that misbehave. To come to consensus, at least 66% of the total staked ether has to vote in favour of a particular set of blocks. Blocks voted for by >=66% of the stake become "finalized", meaning they can't be removed or reorganized.
	Attacking the network can mean preventing the chain from finalizing or ensuring a certain organization of blocks in the canonical chain that somehow benefits an attacker. This requires the attacker to divert the path of honest consensus either by accumulating a large amount of ether and voting with it directly or tricking honest validators into voting in a particular way. Sophisticated, low-probability attacks that trick honest validators aside, the cost to attack Ethereum is the cost of the stake that an attacker has to accumulate to influence consensus in their favour.
	The lowest cost of attack is >33% of the total stake. An attacker holding >33% of the total stake can cause a finality delay simply by going offline. This is a relatively minor problem for the network as there is a mechanism known as the "inactivity leak" that leaks stake away from offline validators until the online majority represents 66% of the stake and can finalize the chain again. It is also theoretically possible for an attacker to cause double finality with a little over 33% of the total stake by creating two blocks instead of one when they are asked to be a block producer and then double-vote with all of their validators. Each fork only requires 50% of the remaining honest validators to see each block first, so if they manage to time their messages just right, they may be able to finalize both forks. This has a low likelihood of success, but if an attacker was able to cause double-finality, the Ethereum community would have to decide to follow one fork, in which case the attacker's validators would necessarily be slashed on the other.
	With >33% of the total stake, an attacker has a chance to have a minor (finality delay) or more severe (double finality) effect on the Ethereum network. With more than 14,000,000 ETH staked on the network and a representative price of $1000/ETH, the minimum cost to mount these attacks is `1000 x 14,000,000 x 0.33 = $4,620,000,000`. The attacker would lose this money through slashing and get ejected from the network. To attack again, they would have to accumulate >33% of the stake (again) and burn it (again). Each attempt to attack the network would cost >$4.6 billion (at $1000/ETH and 14M ETH staked). The attacker is also ejected from the network when they are slashed, and they have to join an activation queue to rejoin. This means the rate of a repeat attack is limited not only to the rate the attacker can accumulate >33% of the total stake but also the time it takes to onboard all their validators onto the network. Each time the attacker attacks, they get much poorer, and the rest of the community gets richer, thanks to the resulting supply shock.
	Other attacks, such as 51% attacks or finality reversion with 66% of the total stake, require substantially more ETH and are much more costly to the attacker.
	Compare this to proof-of-work. The cost of launching an attack on proof-of-work Ethereum was the cost of consistently owning >50% of the total network hash rate. This amounted to the hardware and running costs of sufficient computing power to outcompete other miners to compute proof-of-work solutions consistently. Ethereum was mostly mined using GPUs rather than ASICs, which kept the cost down (although had Ethereum stayed on proof-of-work, ASIC mining may have become more popular). An adversary would have to purchase a lot of hardware and pay for the electricity to run it to attack a proof-of-work Ethereum network, but the total cost would be less than the cost required to accumulate enough ETH to launch an attack. A 51% attack is ~[20x less](https://youtu.be/1m12zgJ42dI?t=1562) expensive on proof-of-work than proof-of-stake. If the attack was detected and the chain hard-forked to remove their changes, the attacker could repeatedly use the same hardware to attack the new fork.
	In proof-of-stake, validators are required to escrow ("stake") at least 32 ETH in a smart contract. Ethereum can destroy staked ether to punish validators that misbehave. To come to consensus, at least 66% of the total staked ether has to vote in favour of a particular set of blocks. Blocks voted for by >=66% of the stake become "finalized", meaning they can't be removed or reorganized.
	#### What is an attack {#what-is-an-attack}
	Attacking the network can mean preventing the chain from finalizing or ensuring a certain organization of blocks in the canonical chain that somehow benefits an attacker. This requires the attacker to divert the path of honest consensus either by accumulating a large amount of ether and voting with it directly or tricking honest validators into voting in a particular way. Sophisticated, low-probability attacks that trick honest validators aside, the cost to attack Ethereum is the cost of the stake that an attacker has to accumulate to influence consensus in their favour.
	#### 33% attacks {#33-percent-attacks}
	The lowest cost of attack is >33% of the total stake. An attacker holding >33% of the total stake can cause a finality delay simply by going offline. This is a relatively minor problem for the network as there is a mechanism known as the "inactivity leak" that leaks stake away from offline validators until the online majority represents 66% of the stake and can finalize the chain again. It is also theoretically possible for an attacker to cause double finality with a little over 33% of the total stake by creating two blocks instead of one when they are asked to be a block producer and then double-vote with all of their validators. Each fork only requires 50% of the remaining honest validators to see each block first, so if they manage to time their messages just right, they may be able to finalize both forks. This has a low likelihood of success, but if an attacker was able to cause double-finality, the Ethereum community would have to decide to follow one fork, in which case the attacker's validators would necessarily be slashed on the other.
	With >33% of the total stake, an attacker has a chance to have a minor (finality delay) or more severe (double finality) effect on the Ethereum network. With more than 14,000,000 ETH staked on the network and a representative price of $1000/ETH, the minimum cost to mount these attacks is `1000 x 14,000,000 x 0.33 = $4,620,000,000`. The attacker would lose this money through slashing and get ejected from the network. To attack again, they would have to accumulate >33% of the stake (again) and burn it (again). Each attempt to attack the network would cost >$4.6 billion (at $1000/ETH and 14M ETH staked). The attacker is also ejected from the network when they are slashed, and they have to join an activation queue to rejoin. This means the rate of a repeat attack is limited not only to the rate the attacker can accumulate >33% of the total stake but also the time it takes to onboard all their validators onto the network. Each time the attacker attacks, they get much poorer, and the rest of the community gets richer, thanks to the resulting supply shock.
	#### 51% attacks {#51-percent-attacks}
	Other attacks, such as 51% attacks or finality reversion with 66% of the total stake, require substantially more ETH and are much more costly to the attacker.
	Compare this to proof-of-work. The cost of launching an attack on proof-of-work Ethereum was the cost of consistently owning >50% of the total network hash rate. This amounted to the hardware and running costs of sufficient computing power to outcompete other miners to compute proof-of-work solutions consistently. Ethereum was mostly mined using GPUs rather than ASICs, which kept the cost down (although had Ethereum stayed on proof-of-work, ASIC mining may have become more popular). An adversary would have to purchase a lot of hardware and pay for the electricity to run it to attack a proof-of-work Ethereum network, but the total cost would be less than the cost required to accumulate enough ETH to launch an attack. A 51% attack is ~[20x less](https://youtu.be/1m12zgJ42dI?t=1562) expensive on proof-of-work than proof-of-stake. If the attack was detected and the chain hard-forked to remove their changes, the attacker could repeatedly use the same hardware to attack the new fork.