Comment by DINKDINK | Hacker News Reader

Comment by DINKDINK | Hacker News Reader

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>There are other coins that already use PoS.

There are some coins that use PoS as a voting mechanism not a consensus mechanisms. If you so desired, you could do the same in any PoW chain.

>How is it a ploy?

Broadly small-game fallacy[1]. If PoS would work at scale ethereum developers would have already deployed it. It doesn't work. Why?

An physical analogy for why PoS can never achieve BFT is: Assume 1) A cryptographic hash function is not broken 2) you live in a cave and you cannot talk the outside world

You are given a letter with a series of nested hash pointers that could have only been produced if they expended resources to created. There is no way this could have been faked, even though you live in a cave, you can trust the message. PoW is a stable BFT solution.

Another version of you in PoS land is also in a cave. You receive a message. It has a list of Arcade tickets that are signed by other Arcade tickets. In order to trust the veracity of this message you have to hope that someone else outside of your cave also saw this message to you because if they haven't, you could be being eclipse attacked, consequently defrauded. You cannot trust that this message hasn't been forged without contacting other people or hoping that other people have see this message. It's not stable it's not a solution to BFT. It's why after 4 years and counting Ethereum still hasn't implemented it.

[1] https://unenumerated.blogspot.com/2015/05/small-game-fallaci...

Why? Easy, people kept figuring out attacks so they kept working on better designs. Figuring out a solid PoS protocol is nontrivial.

A few days ago Vitalik went through the history of Ethereum's proof of stake research at the annual Devcon, if anyone's interested: https://www.youtube.com/watch?v=Km9BaxRm1wA

At this point they're pretty happy with the protocol, the spec is mostly written, and eight teams are working on clients. The new design includes blockchain sharding for about 1000X better scaling.

Regarding your analogy, regardless of protocol you have a certain amount of "weak subjectivity," in that you at least have to know what client software to run. Otherwise you might be accepting invalid blocks.

The attacks you mention can be handled by requiring stake to be locked up for several months, and slightly broadening the subjectivity you accept to include a periodic known blockhash. You have to use off-chain social means to find out the correct recent hash, but you have to do the same to find out the correct software to run. https://blog.ethereum.org/2014/11/25/proof-stake-learned-lov...

>you at least have to know what client software to run

The beauty of PoW is that you don't. By examining a PoW blockchain one can determine the relative amount of work expended. That provides trust with little to no external information. (All you need to know is the relative difficulty of hash functions and what info is hashed to form a block, both independently verifiable).

With PoS there is no analog. You must get your 'trust' externally, through deciding which codebase/client you want to use. Without external information / sidechannels, you have no way of determining which client nor which history to trust.

If a 51% attacker makes an invalid transaction, you actually don't want to accept it just because they have more hashpower; if you did then 51% attackers could arbitrarily steal funds. If you don't accept invalid transactions, then you're using external knowledge of current validation rules.

Also, if you really assume that only the chain with the most hashpower is the valid one, then you have to ignore all other blockchains. And even then, you're assuming you know the correct hash function; given ASICs it's not practical to know what hash function requires the most economic effort just by looking at it.

Knowledge of consensus rules is the knowledge you’re building consensus upon. It’s a given.

But you have to get that knowledge, and the specific software to implement it, from some source other than the blockchain. In practical terms, it barely changes the security model if the download for new users includes a known blockhash from several months back, instead of only the hash of block zero.

Barely but importantly. With bitcoin for every user it is still feasible even on raspberry pi to download and verify the whole chain for themselves. Not so for ethereum even with high end computers. I guess that is their way to phase in PoS scam, but it has nothing to do with “preserving the security model”.

Utxo commitment is definitely a shortcut that bitcoin will eventually implement, but it can only work reliably for long timeframes especially when you have “disturbances in the force” like what happened with BCH last year.

“Known” blockhash from several months back is something that can easily be faked unless you actually fetch all the history and verify.

Ouroboros Genesis solves this problem.

nope, it doesn’t.

Voting and consensus are the same thing.

Only when you can control who can vote (Paxos) Not when systems can fail or lie (PoW/Nakamoto Consensus)

Voting is sybill vulnerable.

I agree with your general idea that PoW is still superior to, or at least more necessary than, PoS, but voting in a PoS system is not sybil vulnerable because you have to lock a resource. If you assume an attacker has enough resource to lock through a sybil attack then they would have the resource available to control a PoW system anyway.

The point is the resource has to be external (i.e. outside of the consensus system) in order to be invulnerable to sybil attacks. In PoW this external resource is computing power, while in PoS it is the resource of the system itself (which might be internal to the consensus system, but has to necessarily be gained externally).

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