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What you are referring to is an old problem (arguably now solved) called “nothing at stake.” Short, bastardized answer is that something built into the consensu

What you are referring to is an old problem (arguably now solved) called “nothing at stake.” Short, bastardized answer is that something built into the consensus code called “slashing” keeps the validators/shakers from trying to stake two versions of a block.

spywaregorilla 4y ago
Who gets to run a slasher node and who gets to agree that its valid to slash a block?
- immibis 4y ago
  I don't know the specific rules for Ethereum, but in general PoS systems, anyone can slash. All you have to do is submit two different headers for the same block signed by the same validator. This proves the validator is cheating. The person who submits the proof may get to keep some of the validator's slashed money, which is a good incentive to run slashing nodes as this can amount to thousands of dollars per slash, and a good incentive not to double-validate as this can amount to thousands of dollars per time you are caught. Perversely, since double-validation happens rarely, since it is expensive, the actual interface for slashing on e.g. BSC is not well-documented or user-friendly.
  - spywaregorilla 4y ago
    > This proves the validator is cheating. To whom? Who gets to decide to slash the funds? I caught you cheating and can prove it. You don't give a shit and control 51% of the network. How do you get punished?
    - bhaak 4y ago
      Social slashing. The honest parts of the community would organize and fork you away. If you were following the current events on Ethereum, this question has just arisen in the last weeks when the US sanctioned the privacy oriented Tornado Cash contract.
    - tromp 4y ago
      You're right that for a slash to be publicly verifiable, the cheating evidence has to appear on-chain. So indeed there is the question of whether this evidence can be censored...
    - rglullis 4y ago
      If you control 51% of the network (actually, with Ethereum PoS that number is 67%, as you need 2/3 of the validators to control consensus) and people know you are malicious, people will abandon the network and you will lose your investment because no one is interested in participating in a network controlled by a crook. It's no different from what would happen in PoW. Can you please stop with the concern trolling?
      - spywaregorilla 4y ago
        > If you control 51% of the network (actually, with Ethereum PoS that number is 67%, as you need 2/3 of the validators to control consensus) and people know you are malicious, people will abandon the network and you will lose your investment because no one is interested in participating in a network controlled by a crook. If that 67% is also true of the slasher voting protocol, then that means you just need 33% of the network to avoid being slashed. Is that wrong? > Can you please stop with the concern trolling? Can you please stop trying to claim a moral high ground for no reason?
        rglullis 4y ago
        > just need 33% of the network to avoid being slashed. Is that wrong? Yes, it is wrong.
        spywaregorilla 4y ago
        How is it wrong? If you need 67% consensus to approve a transaction, and slashing is a transaction, then you can prevent slashing with 33%. What's incorrect about that reasoning?
        rglullis 4y ago
        You won't be prevent slashing with 1/3, you will be merely delaying the block production each time is is proposed. Every time your 1/3 of the nodes attempt maliciously delays of production of a valid block, you will be slashed, and then you won't have 1/3 of the required funds at stake anymore.
    - ahahahahah 4y ago
      The people you are discussing this with clearly have no idea how the system actually works and are far out of their depth as far as considering the ways malicious actors interact with it.
    - immibis 4y ago
      If you control 51% of the network, the network is fucked. If you control 20% of the network, the other 80% is following the rules and colluding against you. (Even another 20% that are double-validating themselves are incentivized to slash you)
  - addaon 4y ago
    In a general PoS system like you describe, what prevents a bistable situation from emerging? If there is any significant level of cheating, then running a slasher is profitable, which makes cheating very unprofitable, driving it to zero. But in the absence of cheating, what's the motivation to develop, maintain, test, and operate a slasher node? Isn't this prone to long periods of time with negligible cheating where all the slashers die out, followed by one big malicious attack that isn't caught promptly?
    - immibis 4y ago
      Possibly. You could even do this if the slashers were active. Just start up your attack instantaneously in between two blocks. Prior to the attack, nobody is cheating. After the attack, nobody is accepting evidence of cheating. The whole cryptocurrency thing feels like a bit of a metastable equilibrium, but nobody's figured out anything better. Arguably even government-controlled fiat money is not much better - if >50% of the population doesn't like the rules, they will change them - we may be seeing the beginning of this right now, with a lot of people getting dissatisfied with half their income going to the black hole known as "landlords" who own the rights to take your income without producing any value whatsoever. It might just lead to everyone abandoning your cryptocurrency and using a different one. Since you had to have >50% of the cryptocurrency in order to conduct the attack, you did lose a substantial amount of real-world value (billions or trillions of $) when everyone else stopped using your cryptocurrency. It's pretty much analogous to if a majority of PoW miners decide to "go their own way" and make a chain where nobody else is invited. What happens then?

spywaregorilla 4y ago

Who gets to run a slasher node and who gets to agree that its valid to slash a block?

immibis 4y ago
I don't know the specific rules for Ethereum, but in general PoS systems, anyone can slash. All you have to do is submit two different headers for the same block signed by the same validator. This proves the validator is cheating. The person who submits the proof may get to keep some of the validator's slashed money, which is a good incentive to run slashing nodes as this can amount to thousands of dollars per slash, and a good incentive not to double-validate as this can amount to thousands of dollars per time you are caught. Perversely, since double-validation happens rarely, since it is expensive, the actual interface for slashing on e.g. BSC is not well-documented or user-friendly.
- spywaregorilla 4y ago
  > This proves the validator is cheating. To whom? Who gets to decide to slash the funds? I caught you cheating and can prove it. You don't give a shit and control 51% of the network. How do you get punished?
  - bhaak 4y ago
    Social slashing. The honest parts of the community would organize and fork you away. If you were following the current events on Ethereum, this question has just arisen in the last weeks when the US sanctioned the privacy oriented Tornado Cash contract.
  - tromp 4y ago
    You're right that for a slash to be publicly verifiable, the cheating evidence has to appear on-chain. So indeed there is the question of whether this evidence can be censored...
  - rglullis 4y ago
    If you control 51% of the network (actually, with Ethereum PoS that number is 67%, as you need 2/3 of the validators to control consensus) and people know you are malicious, people will abandon the network and you will lose your investment because no one is interested in participating in a network controlled by a crook. It's no different from what would happen in PoW. Can you please stop with the concern trolling?
    - spywaregorilla 4y ago
      > If you control 51% of the network (actually, with Ethereum PoS that number is 67%, as you need 2/3 of the validators to control consensus) and people know you are malicious, people will abandon the network and you will lose your investment because no one is interested in participating in a network controlled by a crook. If that 67% is also true of the slasher voting protocol, then that means you just need 33% of the network to avoid being slashed. Is that wrong? > Can you please stop with the concern trolling? Can you please stop trying to claim a moral high ground for no reason?
      - rglullis 4y ago
        > just need 33% of the network to avoid being slashed. Is that wrong? Yes, it is wrong.
        spywaregorilla 4y ago
        How is it wrong? If you need 67% consensus to approve a transaction, and slashing is a transaction, then you can prevent slashing with 33%. What's incorrect about that reasoning?
        rglullis 4y ago
        You won't be prevent slashing with 1/3, you will be merely delaying the block production each time is is proposed. Every time your 1/3 of the nodes attempt maliciously delays of production of a valid block, you will be slashed, and then you won't have 1/3 of the required funds at stake anymore.
  - ahahahahah 4y ago
    The people you are discussing this with clearly have no idea how the system actually works and are far out of their depth as far as considering the ways malicious actors interact with it.
  - immibis 4y ago
    If you control 51% of the network, the network is fucked. If you control 20% of the network, the other 80% is following the rules and colluding against you. (Even another 20% that are double-validating themselves are incentivized to slash you)
- addaon 4y ago
  In a general PoS system like you describe, what prevents a bistable situation from emerging? If there is any significant level of cheating, then running a slasher is profitable, which makes cheating very unprofitable, driving it to zero. But in the absence of cheating, what's the motivation to develop, maintain, test, and operate a slasher node? Isn't this prone to long periods of time with negligible cheating where all the slashers die out, followed by one big malicious attack that isn't caught promptly?
  - immibis 4y ago
    Possibly. You could even do this if the slashers were active. Just start up your attack instantaneously in between two blocks. Prior to the attack, nobody is cheating. After the attack, nobody is accepting evidence of cheating. The whole cryptocurrency thing feels like a bit of a metastable equilibrium, but nobody's figured out anything better. Arguably even government-controlled fiat money is not much better - if >50% of the population doesn't like the rules, they will change them - we may be seeing the beginning of this right now, with a lot of people getting dissatisfied with half their income going to the black hole known as "landlords" who own the rights to take your income without producing any value whatsoever. It might just lead to everyone abandoning your cryptocurrency and using a different one. Since you had to have >50% of the cryptocurrency in order to conduct the attack, you did lose a substantial amount of real-world value (billions or trillions of $) when everyone else stopped using your cryptocurrency. It's pretty much analogous to if a majority of PoW miners decide to "go their own way" and make a chain where nobody else is invited. What happens then?