Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

On blockchains and why secure ledgers don't require proof-of-work

pfrazee.github.io

Post reply on HN
Print view View original

21–30 of 61 posts

Re: On blockchains and why secure ledgers don't require proof-of-work

#21

Post by pfraze »

wmf wrote: post #18
bmcusick wrote: post #14

Ugh. He completely misunderstands what PoW (or PoS) are for. The entire point of PoW is deciding between two valid & correct blockchain states. Alice owns a bitcoin. Alice validly signs a transaction transferring that bitcoin to Bob. Alice also validly signs a transaction transferring that same bitcoin to Charles. WHICH IS CORRECT? Neither is a forgery. Both signatures are valid. If Dave downloads the blockchain, or…

I think the point is that, hypothetically, some non-financial systems don't require ordering or conflict resolution and thus such systems don't need PoW.

Actually I appreciate the defense, but that's not what I'm claiming. I'm claiming that decentralized consensus gives only a minor gain over a single node maintaining a well-monitored blockchain. Single nodes don't have the problems of uncertain ordering or conflict resolution because they can provide strict consensus.

Re: On blockchains and why secure ledgers don't require proof-of-work

#22

Post by rocqua »

hagreet wrote: post #4
pfraze wrote: post #3

Earlier quoted context omitted.

You don't use decentralized consensus in this model. It's a single node that's maintaining the blockchain state. Monitors actively watch the blockchain to make sure the node doesn't deviate from the code contract. If there is a fork in the blockchain, that'd be because the single node created that fork in an attempt to create two versions of the state-- that's a break in the contract and it would be viewed as a fatal…

So essentially you need a trusted third party and if that party stops being trustworthy you have to start from scratch?

Yes, if you can handle forks as long as you can detect them, centralized consensus is a decent solution with much lower costs that PoW.

This is essentially how CT-logs work, where we consider it sufficient to detect a falsely-issued certificate, even though we cannot prevent such issuance.

Re: On blockchains and why secure ledgers don't require proof-of-work

#23

Post by pfraze »

EGreg wrote: post #13
pfraze wrote: post #6

Earlier quoted context omitted.

Semi-trusted. You have total transparency into whether the node is following the rules of the code contract. The node could not, for instance, change values in the DB without doing so via the contract, and that would be logged for all to see. Very important for something like a key server. There are two things you have to trust, which I mention in the post. 1. That the node is not denying writes. (What's sometimes in…

Sure it can - it can just start reporting different things to different validators. At this point the validators compare notes and gossip a proof that the node's been acting up. And then they need to elect another node, which requires... consensus! Oh and the central node can also become unavailable and DDOSed, how are you going to add transactions to the ledger then?

Choosing another node won't involve consensus in the way that consensus is described in distributed networks. You'd handle that ideally by a prior agreement -- eg, "if this node corrupts, it's going to go into arbitration via a trusted third party, who will then decide who will resume operating the network."

Re: On blockchains and why secure ledgers don't require proof-of-work

#24

Post by rocqua »

EGreg wrote: post #11
hagreet wrote: post #2

So if there is no proof of work how do you avoid forks? The author says something about splits being detectable but that doesn't really help us decide on which side of the split is correct.

I think this obsession with consensus is a fad. Forks are ok as long as they can be merged in the short term. If something forks for a long time and stays forked, there is hardly any reason to establish a total order during the merge! Think of an IRC netsplit for example. One that happens for a few seconds may attempt to merge back the chats in some fair order they were made, in diff forks. But if the netsplit happen…

In the specific case of currency, practical double spends are a real issue. 'Merging' the state after a double spend requires either forcing the double spender to pony-up, or taking back money from those who received it without being aware of any wrongdoing. That is, unless you are fine with people printing their own currency.

This is rather unique to the case of currency though. Specifically, the history of transactions determines which future transactions are possible. Instead a system that only records promises (but doesn't allow transfer of such promises) would work without centralization. If I promise something to 2 different people I remain on the hook for that promise. The fact that I am effectively 'in debt' on the system isn't an issue because the system gives no guarantees on people meeting their promises.

Re: On blockchains and why secure ledgers don't require proof-of-work

#25

Post by rocqua »

EGreg wrote: post #9

Straw man. Blockchain consensus algorithms don't only use proof of work. We have proof of stake, delegated proof of stake like LISK, proof of Correctness like Ripple (my personal favorite), and so on. No need for a wasteful arms race just to elect a leader who can be DDOSed.

A very quick look at ripple leads to my following interpretation.

"ripple is voting with a consensus level of 80%, so it can tolerate byzantine failure of 20% of all nodes". My question is then, how does this deal with sibyl attacks. That is, how does it prevent me from just creating a large amount of participants. Similarly, what happens when nodes 'leave' the system.

Say we have 200 nodes, then the consensus level is 160 nodes. What happens when 10 nodes stop responding? Are we forever stuck with the consensus level of 160 or does it ever drop to 152 nodes? In the first case, we are inevitably careening towards faulty nodes forming 20% of all required votes. In the second, we can enforce consensus by censoring other nodes.

Re: On blockchains and why secure ledgers don't require proof-of-work

#26

Post by [deleted] »

pfraze wrote: post #19
bmcusick wrote: post #14

Ugh. He completely misunderstands what PoW (or PoS) are for. The entire point of PoW is deciding between two valid & correct blockchain states. Alice owns a bitcoin. Alice validly signs a transaction transferring that bitcoin to Bob. Alice also validly signs a transaction transferring that same bitcoin to Charles. WHICH IS CORRECT? Neither is a forgery. Both signatures are valid. If Dave downloads the blockchain, or…

> Paul's system has no way of addressing this other than "trust the central authority to process transactions in the order they receive them". Thanks, pal, that's called e-cash, and was invented by David Chaum in 1983. Flatly wrong. Decentralized consensus is not a necessity to create trustless operation. Monitoring service operation via a secure ledger provides trustless operation. As I said, the point of PoW is to…

[deleted]

Re: On blockchains and why secure ledgers don't require proof-of-work

#27

Post by wyldfire »

pfraze wrote: post #19
bmcusick wrote: post #14

Ugh. He completely misunderstands what PoW (or PoS) are for. The entire point of PoW is deciding between two valid & correct blockchain states. Alice owns a bitcoin. Alice validly signs a transaction transferring that bitcoin to Bob. Alice also validly signs a transaction transferring that same bitcoin to Charles. WHICH IS CORRECT? Neither is a forgery. Both signatures are valid. If Dave downloads the blockchain, or…

> Paul's system has no way of addressing this other than "trust the central authority to process transactions in the order they receive them". Thanks, pal, that's called e-cash, and was invented by David Chaum in 1983. Flatly wrong. Decentralized consensus is not a necessity to create trustless operation. Monitoring service operation via a secure ledger provides trustless operation. As I said, the point of PoW is to…

The function of mining is not limited to the PoW, it's also an arbitration mechanism for decentralized minting/scheduled inflation.

The block reward incentivizes participants. Why should I run a monitor node for this new cryptocoin? Who will allocate the coins and how?

> Am I certain that I need strict global consensus?

Perhaps not but IMO it makes things much simpler to design as a result.

Re: On blockchains and why secure ledgers don't require proof-of-work

#28

Post by DINKDINK »

wmf wrote: post #18
bmcusick wrote: post #14

Ugh. He completely misunderstands what PoW (or PoS) are for. The entire point of PoW is deciding between two valid & correct blockchain states. Alice owns a bitcoin. Alice validly signs a transaction transferring that bitcoin to Bob. Alice also validly signs a transaction transferring that same bitcoin to Charles. WHICH IS CORRECT? Neither is a forgery. Both signatures are valid. If Dave downloads the blockchain, or…

I think the point is that, hypothetically, some non-financial systems don't require ordering or conflict resolution and thus such systems don't need PoW.

>hypothetically, some non-financial systems don't require ordering or conflict resolution and thus such systems don't need PoW.

If you don't need trustless time ordering of data, you don't need a blockchain. You just need... a database

Re: On blockchains and why secure ledgers don't require proof-of-work

#29

Post by wyldfire »

pfraze wrote: post #23
EGreg wrote: post #13

Earlier quoted context omitted.

Sure it can - it can just start reporting different things to different validators. At this point the validators compare notes and gossip a proof that the node's been acting up. And then they need to elect another node, which requires... consensus! Oh and the central node can also become unavailable and DDOSed, how are you going to add transactions to the ledger then?

Choosing another node won't involve consensus in the way that consensus is described in distributed networks. You'd handle that ideally by a prior agreement -- eg, "if this node corrupts, it's going to go into arbitration via a trusted third party, who will then decide who will resume operating the network."

IMO this new design is "fine w/me" in the way that ethereum is "fine w/me." If people want a not-so-decentralized cryptocoin that's not-so-trustless, then so be it.

If it handles transactions faster, better, cheaper, and with less emissions, then so be it.

Unfortunately bitcoin's popularity/ubiquity makes it superior (for the time being) and hard to unseat. Other (decentralized) altcoins make really great improvements over bitcoin but never became (and perhaps never will become) as popular as bitcoin.

Re: On blockchains and why secure ledgers don't require proof-of-work

#30

Post by bmcusick »

pfraze wrote: post #19
bmcusick wrote: post #14

Ugh. He completely misunderstands what PoW (or PoS) are for. The entire point of PoW is deciding between two valid & correct blockchain states. Alice owns a bitcoin. Alice validly signs a transaction transferring that bitcoin to Bob. Alice also validly signs a transaction transferring that same bitcoin to Charles. WHICH IS CORRECT? Neither is a forgery. Both signatures are valid. If Dave downloads the blockchain, or…

> Paul's system has no way of addressing this other than "trust the central authority to process transactions in the order they receive them". Thanks, pal, that's called e-cash, and was invented by David Chaum in 1983. Flatly wrong. Decentralized consensus is not a necessity to create trustless operation. Monitoring service operation via a secure ledger provides trustless operation. As I said, the point of PoW is to…

Hi Paul. I'm Brock.

I hope we're not talking at past each other, but I read your post as proposing a system where there's a central party that computes transactions "in the open" in a way that third party observers can verify.

That's hardly useless, but it's not a replacement for Proof of Work. PoW is for decentralizing the ability to choose between competing valid blockchains. It prevents double-spending by making the benefit of double-spending (the value of the your transaction) far less than the cost of double-spending (the electrical cost of 51% of the mining power for 1 hour or so).

Your system uses a centralized host (see "Services with Secure Ledgers", paragraph 2), and (I presume) third-party observers can verify a "secure ledger" by seeing which one has been more recently signed and time-stamped by the single host.

I mean, sure, centrally hosted servers are more efficient than Proof of Work. No one who know what they're talking about disputes that. But the whole point of PoW is to allow decentralization without a single host.

Post reply on HN