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

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

#171

Post by tuesdayrain »

nickpsecurity wrote: post #137
lojack wrote: post #132

Earlier quoted context omitted.

> A key difference is most of the new techs like Internet, email, Paypal, and so on improved on what people already had in a way that delivered obvious value. I'd argue that for most people the value was only obvious afterwards. To put email in perspective, early adopters had to choose between what they already knew and all the hurdles involved in connecting to the internet and using the new technology. There was als…

The thing I was getting at is, if you had a computer and Internet, then email would be a free, fast alternative to traditional mail. That has obvious benefit. Whereas, these currencies are volatile, slower, often dont allow charge backs, use more energy, and accepted at fewer places. Worse in every way to checking accounts and credit cards. Esp if we have multiple cards or accounts to reduce risk of single institutio…

No chargebacks is a feature in many situations.

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

#172

Post by stickfigure »

nickpsecurity wrote: post #137
lojack wrote: post #132

Earlier quoted context omitted.

> A key difference is most of the new techs like Internet, email, Paypal, and so on improved on what people already had in a way that delivered obvious value. I'd argue that for most people the value was only obvious afterwards. To put email in perspective, early adopters had to choose between what they already knew and all the hurdles involved in connecting to the internet and using the new technology. There was als…

The thing I was getting at is, if you had a computer and Internet, then email would be a free, fast alternative to traditional mail. That has obvious benefit. Whereas, these currencies are volatile, slower, often dont allow charge backs, use more energy, and accepted at fewer places. Worse in every way to checking accounts and credit cards. Esp if we have multiple cards or accounts to reduce risk of single institutio…

Worse in every way to checking accounts and credit cards.

Quite a few Venezuelans would beg to differ about that.

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

#173

Post by drb91 »

garmaine wrote: post #113
lukifer wrote: post #106

Earlier quoted context omitted.

Yet another reason why Proof of Stake is destined to outcompete Proof of Work. ;)

Proof of Stake is a perpetual motion machine. You can't safely tie consensus to something (stake) which is determined by consensus. That's circular reasoning and ungrounded.

What would failure look like?

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

#174

Post by Semaphor »

CydeWeys wrote: post #47
Cilvic wrote: post #41

Earlier quoted context omitted.

How is the 51% attack detected?

It's really obvious once the new chain is broadcasted. "Honest" miners switch over to mine on the deepest chain as soon as they become aware of it. It's very rare to even see a 2-block conflict. When you see a large N-block conflict then it's obvious there's a 51% attack going on.

But isn't the point of the whole thing that you do not broadcast it until after you are done? So yes, it's obvious in hindsight, but the damage will be done.

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

#175

Post by labster »

dragontamer wrote: post #128
Scoundreller wrote: post #122

Earlier quoted context omitted.

If a 51% attack is mounted by adding hash power, wouldn’t the existing miners on the target coin also start shutting down[1] because the competition is higher, reinforcing the strength of the attackers? [1] or migrate from to another coin, such as the coin that the attackers left to fill their void?

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.

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

#176

Post by Proven »

The way things are going soon Top 10 PoW will become targets and ultimately BTC.

BTC is hard to attack and not because it's got a ton of hashpower but because it's hard to get paid in any other crypto (if/when payout for asking a successful attack on BTC might be more than USD 10 mil).

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

#177

Post by laverya »

samatman wrote: post #167
pryce wrote: post #144

Earlier quoted context omitted.

The six-blocks-in-a-row problem seems less of an impedence to me - because the "legitimate" blocks are still available to the malicious actor. Therefore, if our malicious miner identifies that they have had poor luck and begun to fall behind the "legitimate" chain by a block or two they can start the make-a-longer-competing-chain process over again from the legitimate head with -as far as I can see- no downsides exce…

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 requires 6 blocks of confirmation, so you need to wait until block 1006 on the public chain before you can actually take delivery. Now that you've done that, you can publish your private chain at block 1007 (or 1008, etc) and since it's the longest chain, it'll be accepted by the public.

You didn't have to get 6 blocks before the public chain got 1 - you only needed to get 1 more block than the public chain, at some point after the public chain has mined 6 more blocks.

  1000 - 1001 - 1002 - 1003 - 1004 - 1005 - 1006          1008      Public Chain
       \ 1001 - 1002 - 1003 - 1004 - 1005 - 1006 - 1007 /           Private Chain

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

#178

Post by askmike »

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.

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 hardware this can sometimes go down a lot more than the value of a coin (which makes the cost of this attack worth it).

As soon as you start introducing measures to subvert this attack you are subverting either decentralization or stability. If you for example program clients to not accept reorgs deeper than 10 blocks (for example) you simply introduce new attack vectors that can split the network (into following different chains - which is even scarier than 51% attacks).

If every x blocks you snapshot the chain and force everyone to follow that snapshot you just centralized the chain, etc.

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

#179

Post by thaumasiotes »

jancsika wrote: post #108
jonahx wrote: post #81

Earlier quoted context omitted.

Would you mind elaborating on this for someone unfamiliar?

Imagine all the Bitcoin miners out there right now using their ASICs to do extremely efficient hashing in the hopes of generating a block reward. Let's didactically suppose there are 100 such miners total. Now imagine Dinkycoin comes along and releases their cryptocurrency that uses the same hashing mechanism for the block reward. Initially they have the block difficulty level pretty low as there aren't that many peo…

> suppose Dinkycoin says you need 20 confirmations before accepting that a transaction "went through."

> Once the Bitcoin miner has a competing branch with greater total difficulty than the rest of the network, the network must accept that branch as the winner.

These statements directly contradict each other. The very, very obvious solution is to say that, if 20 confirmations validate that a transaction happened, then validated transactions can't be rolled back. (They're validated!) Once block 26 comes online, block 6 is a permanent feature of the blockchain. That's the only possible meaning of "accepting that a transaction went through". And, note, that is the definition being used now to label this an "attack" rather than "huh, look what happened".

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

#180

Post by retsibsi »

xur17 wrote: post #155
butisaidsudo wrote: post #153

Earlier quoted context omitted.

I'm trying to understand what "cashing out" would look like in an attack like this. One option would be to send coins to an exchange as you mentioned, and I presume cash them out before publishing your longer chain. However, after the attack wouldn't it be easy to compare both chains and see which coins were double spent? Wouldn't you obviously be the perpetrator, having both double spent, as well as having cashed ou…

It absolutely would be easy to compare both chains and see exactly which coins were double spent, and you'd obviously be the perpetrator. Not that I advocate it, but if you wanted to carry out an attack, you'd likely target an exchange that didn't require verification, and you might exchange and withdraw under another coin (ex: trade ETC for ETH). Then spend and/or clean your ill-gotten gains.

Genuine question, forgive me if it's stupid: what happens immediately after you publish the blocks? Maybe I've misunderstood a step, but I think at this point you're in possession of a) whatever real-world goods or other currencies you bought with your bitcoins from the old chain, plus b) the same number of bitcoins on the new chain. Am I right that the value of bitcoin is now likely to crash rather quickly, as people inevitably realise what you've done? Is it just a question of completing the second spend quickly enough, before this happens?
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