We can confirm that there was a successful 51% attack on Ethereum Classic • Hacker News Board

Re: We can confirm that there was a successful 51% attack on Ethereum Classic

#211

Post by rini17 » Tue, Jan 08, 2019, 10:44 AM UTC

askmike wrote: post #178

labster wrote: post #175

Earlier quoted context omitted.

If only we had a currency that was immune to 51% attacks because a government was willing to use force to preserve its value, and therefore doesn't need a massive use of energy for its proof of work.

We call it a 51% attack an attack, but from the perspective of PoW it's always about the chain with the most work. Anyone is just as valid as anyone else to propose blocks. That's the point of Bitcoin: a way to always figure what the truth is, and make it as expensive as possible for people to attack/change this truth. The only problem here is that PoW only knows one cost: hashing, and due to macro shifts in mining h…

Due to probabilistic nature of most PoW protocols, you don't actually need to have the chain with the most work. Attacker can keep trying till they are are lucky, with less than 50% hashpower.

Re: We can confirm that there was a successful 51% attack on Ethereum Classic

#212

Post by simias » Tue, Jan 08, 2019, 10:50 AM UTC

johndunne wrote: post #30

leevlad wrote: post #27

Earlier quoted context omitted.

I think it's just not worth the time. What do you do when you've successfully run a 51% attack? You go on an exchange and double spend the money, which means you have to maintain the 51% attack for longer than min # of confirmations for this currency on said exchange. And even after that, most exchanges (in NA at least, can't say much about intl) require KYC.

Exactly, it's not worth the time. And once the attack is underway, it'll be detected and everyone can simply increase the number of confirmations needed before finalising.

Increasing the number of confirmations is easy but it also slows down everything. People don't want to have to wait for days for their transactions to be accepted.

If I understand correctly this attack managed to reorganize hundreds of blocks. That's a lot of time to wait for confirmations.

Re: We can confirm that there was a successful 51% attack on Ethereum Classic

#213

Post by samatman » Tue, Jan 08, 2019, 10:55 AM UTC

laverya wrote: post #177

samatman wrote: post #167

Earlier quoted context omitted.

They still have to get out ahead by six blocks, however. This drops to zero every time they start over, so it doesn't change the basic calculus.

They don't need to get ahead by six blocks. They need to get ahead, with at least six blocks mined on the public chain. There's a massive difference there! The chain starts at block 1000, and you make a spend that will be included at block 1001 on the public chain. At the same time, you start mining your private chain from block 1000 (and you don't include that transaction in it). Now, the exchange you're using requi…

I take your point.

We're saying the same thing, but I see now that this was unclear.

The point of this sub-thread is that 51% doesn't give you a guarantee you'll mine faster than the 49%, just an edge, and that edge narrows as more blocks are required.

A casino with a 1% house advantage would have days when it was in the red, around 178 of them in fact. By analogy, you need to line up six days in the black, in a row.

The chance of doing that is lower than 51%.

Re: We can confirm that there was a successful 51% attack on Ethereum Classic

#214

Post by Pyxl101 » Tue, Jan 08, 2019, 11:23 AM UTC

thaumasiotes wrote: post #208

Robin_Message wrote: post #200

Earlier quoted context omitted.

So, I just ran through the same thought process and the problem is this: How does a new entrant to the network know which is the valid chain? They didn't see the previous 20 confirmations, so the only rule they can use is picking the longest chain. Another way to do it is to have a separate voting system to attest to the "valid" chain, but then you could use an ordinary botnet to outvote the real chain. In short, con…

I don't follow this. A new entrant to the network knows which is the valid chain because the chain the network uses defines "the network". Consider the case[1] of Ethereum Classic (ETC) versus Ethereum (ETH). They are exactly the same, except for the chain each group of miners follows. The ETC blockchain is a valid ETH blockchain and the ETH blockchain is a valid ETC blockchain, but miners adhere to one or the other…

What you're missing is the process by which new blocks are added onto an existing chain. Let's say that you take the "true" Bitcoin or ETC blockchain, if you want to think of it that way, and now multiple actors are proposing to add blocks onto it, potentially multiple blocks. Which one of those additions wins? The one that's the longest and has the most work behind it - that one wins.

If you propose an addition that is one block long, and I propose an addition that's 2 blocks long, then my chain wins. (These all have to be valid blocks that solve the mining challenge). Miners select the chain with the most work. That's the consensus mechanism by which the blockchain is established (among nodes operating all with the same rule sets).

At any given instantaneous point in time, there may be multiple instantaneous forks of the main blockchain - people who have mined out valid next blocks and are fighting to get them accepted as the primary chain. Imagine that two different miners by coincidence mine out the next block. One of those chains has to win. The chain that wins is the one that propagates through the network most quickly such that other miners begin building upon it and extending the chain - the one with the most work wins. The other chain(s) die and the transactions on it have to be resubmitted.

When multiple branches exist on the blockchain, some consensus process has to reconcile which of them wins. That process is that miners select the longest chain. Don't act as if one single block is magically appended to the chain and everyone knows which block that is; a consensus process operates to select that block (or sequence of blocks), and it operates by selecting the longest chain. When two or more blocks are mined out simultaneously by different miners, the one that wins is likely to be the chain that propagates more quickly to other miners. Since miners build on the longest chain, then the miner who distributes their chain more widely among other miners is likely to win, since those miners will begin building upon it (seeing it as the longest chain thus far).

To continue the story, let's say that you and I both simultaneously mine out the next block of Bitcoin. You don't tell anyone about your block, and keep it to yourself. I distribute my block to the entire network. Thus, other miners start building on my block, and it becomes part of the main bitcoin blockchain. Once that happens, it doesn't matter if you start telling other people about your block -- it's not part of bitcoin any more because my chain exists which is much longer (my block + whatever other blocks people have mined out on top of it).

Re: We can confirm that there was a successful 51% attack on Ethereum Classic

#215

Post by rando444 » Tue, Jan 08, 2019, 11:24 AM UTC

labster wrote: post #175

dragontamer wrote: post #128

Earlier quoted context omitted.

51% attackers mine in secret. Basically, you spend your coins today, while controlling a 51% share. When everyone else's 49% hash-power creates 98 blocks, your 51% share will create 102 blocks. But secretly. That's the key. Now that your chain is +4 ahead (or wait even longer and become +10 ahead), you can spend your coins on the public chain. Then, you publish your 102 alternative blocks (which barely adds any hash…

If only we had a currency that was immune to 51% attacks because a government was willing to use force to preserve its value, and therefore doesn't need a massive use of energy for its proof of work.

Estonia was planning (and announced) something along these lines .. but the EU basically told them no.

https://www.bloomberg.com/news/articles/2018-06-01/estonia-c...

Re: We can confirm that there was a successful 51% attack on Ethereum Classic

#216

Post by rando444 » Tue, Jan 08, 2019, 11:27 AM UTC

matte_black wrote: post #159

vasilipupkin wrote: post #102

Earlier quoted context omitted.

51% attacks are quite possibly wire fraud so I would refrain from bragging about them. More accurately, trying to double spend the coins is wire fraud.

Which government will prosecute?

The person they are swindling can go through their own authorities, and if the authorities in the criminal's country are alerted to his activities, they can go after them as well.

Theft and fraud don't take on different meanings just because the currency is digital.

Re: We can confirm that there was a successful 51% attack on Ethereum Classic

#217

Post by ahje » Tue, Jan 08, 2019, 11:42 AM UTC

oblio wrote: post #183

stickfigure wrote: post #172

Earlier quoted context omitted.

Worse in every way to checking accounts and credit cards. Quite a few Venezuelans would beg to differ about that.

So for cryptocurrencies to be the "better solution" you just need your entire country to have a total meltdown lasting multiple years?

> you just need your entire country to have a total meltdown

That happens more often than one might think. There are quite a few countries, that are currenly on the brink of collapse, so it is not unlikely that one or more of them will adopt a cryptocurrency some time in the not to far-off future.

Re: We can confirm that there was a successful 51% attack on Ethereum Classic

#218

Post by bouncycastle » Tue, Jan 08, 2019, 11:45 AM UTC

setr wrote: post #201

bouncycastle wrote: post #170

Earlier quoted context omitted.

Yes, of course! And once the damage has been done, it's even harder to reverse. Perhaps if Dinkycoin's devs are fast enough, they could release a fork to undo it?

As long as the attacker maintains 51%, he can eventually just repeat the attack, regardless of the number of forks.

Ooohchie, yes indeed!

Re: We can confirm that there was a successful 51% attack on Ethereum Classic

#219

Post by vvillena » Tue, Jan 08, 2019, 11:51 AM UTC

thaumasiotes wrote: post #197

askmike wrote: post #192

Earlier quoted context omitted.

> They do; for a transaction to be revocable means you haven't accepted that it went through. If every block is revocable indefinitely, then you can't say that 20 confirmations confirm a block, because they don't. From the blockchain perspective a block with a confirmation is confirmed. But everyone else can make new rules on top regarding payments: Do you consider most crypto exchanges to not support "Bitcoin" since…

>> With a consensus of decentralized, less-than-perfectly-synchronized miners, you'd want a fuzzier boundary -- which is what "wait for 20 following transactions" provides. > This is done to raise the cost of reversing the transaction (the more confirmations deep, the more expensive your attack needs to be). No, it isn't done at all. You state as much: > From the blockchain perspective a block with a confirmation is…

The original Bitcoin white paper explains this pretty well. The Bitcoin blockchain is never frozen, and the longest (the hardest) chain is always the valid one. The paper includes a formula to calculate the probability of a block being replaced by another, and sets 6 confirmations as the frontier where it is almost impossible for the chain to change.

What the paper doesn't say is that the formula doesn't work if there is more than one chain. Since an ETH miner can easily switch to ETC at any time, proof-of-work isn't really protecting ETC at all. There is another chain that was a lot harder to calculate, which means the ETC chain stands on thin ice.

Why not freeze the blockchain at certain points, then? Well, it cannot be easily done. There is the problem of choosing which blocks should be frozen, and when. How do you calculate that? What if there's a network split at that time? What happens if the protocol results in an unwanted fork? What happens if malicious actors try to settle on a wrong chain? This is the very problem that Bitcoin solved. Forgetting the idea of a final truth, and making the blocks work like a wave of consensus that eventually reaches everyone. Clever and simple, but with some drawbacks that have to be understood.

Of course, there are lots of people working on new ways of establishing decentralized consensus. The Ethereum devs have been working hard on this for a few years.

Re: We can confirm that there was a successful 51% attack on Ethereum Classic

#220

Post by Applejinx » Tue, Jan 08, 2019, 11:56 AM UTC

zeroname wrote: post #60

semi-extrinsic wrote: post #22

Earlier quoted context omitted.

How can there be coins with $5M+ market cap where the cost of a 51% attack is $3.00 ?? In an efficient market, thieves should just immediately attack that. Or is the benefit too low?

The only way to profit is to double-spend, so you'll have to buy or already own a substantial amount of those junk coins and then sell them. After you performed the attack, those coins that you now could theoretically sell again may be suspended from trading or should at least trade at a substantially lower price. Add in the opportunity cost of exercising such an attack and it's not clear that you could turn a profit…

Or, if you have any other motivation for attacking either a coin or a person or entity known to be heavily invested in that coin.

You know, in case turning a profit is not the only possible motivation for anybody to do anything. Many acts of war and violence are not profitable, certainly not directly profitable, and yet history shows people will attack each other anyhow.

'Bit' worrisome if your whole concept of finance depends on altruistically greedy actors who can never act out of spite or malice. That would be creepy but nice compared to the real world as it has always existed.