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Bitcoin Gold Hit by Double Spend Attack, Exchanges Lose Millions

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Re: Bitcoin Gold Hit by Double Spend Attack, Exchanges Lose Millions

#231

Post by Cogito »

hartator wrote: post #180

Stupid question: If an attack allows to successfully double spend, can you also triple spend or quadruple spend?

Well sort of.

Double spending is just convincing the network you've sent coins to multiple places, and then undoing all of the transactions that were 'paying' for something (in this case paying for credits at an exchange).

The actual details of what they were doing matters and I don't know them, but it's almost certainly simpler to chain double spends together, one after the other, than to try and do three or more transactions concurrently then reverse most of them.

This achieves the same thing as a triple or quadruple spend but only necessitates reversing one transaction at a time.

Re: Bitcoin Gold Hit by Double Spend Attack, Exchanges Lose Millions

#232

Post by root_axis »

I'm just waiting for the day when it's revealed that ~70% of miners on a top 5 cryptocurrency are compromised by a specialized worm or malware. We'll probably only find out after the double spending is discovered but this type of outcome seems almost inevitable. The people writing this type of software are definitely financially motivated, but I can easily imagine such a person throwing away millions of dollars in 0-days just to fulfill such a hackneyed cyberpunk cliche.

Also, we know that things like stuxnet exist. Imagine something even a fraction as crazy as that targeting mining nodes. It's going to happen eventually.

Re: Bitcoin Gold Hit by Double Spend Attack, Exchanges Lose Millions

#233

Post by hinkley »

XR0CSWV3h3kZWg wrote: post #6

more details here: https://forum.bitcoingold.org/t/double-spend-attack-on-excha... Bitcoin gold was a fork to try and decentralize mining. It changed to a proof of work that is supposed to be ASIC resistant. It looks like the typical situation is mining by GPU for equihash (BTG PoW). BTG hashrate is at ~30MH/s at the moment, where Zcash's hashrate is at ~486MH/s. I don't have the numbers off hand, but it'd be interes…

Not every distributed consensus algorithm is happy with 51%. If you increased the minimum to 60% you’d increase the number of machines the attacker requires by 50%.

If 100 machines play fair, >50% requires 101 evil machines, but >60% requires 151 evil machines.

Re: Bitcoin Gold Hit by Double Spend Attack, Exchanges Lose Millions

#234

Post by cozzyd »

XR0CSWV3h3kZWg wrote: post #143
s73v3r_ wrote: post #116

Earlier quoted context omitted.

"It changed to a proof of work that is supposed to be ASIC resistant." These are the absolute worst. All they're doing is causing the cost of graphics cards to go up.

It's great if you own NVDA!

Maybe Nvidia is responsible for it

Re: Bitcoin Gold Hit by Double Spend Attack, Exchanges Lose Millions

#235

Post by IkmoIkmo »

apo wrote: post #216

Oddly enough, one of the selling points of Bitcoin Gold (a hard fork of Bitcoin) was its use of Equihash instead of SHA-256. The idea was that a memory-hard proof-of-work function would inoculate Bitcoin Gold from miner centralization. The problem with mining centralization is that sufficiently powerful miners can attack the network by rewriting blocks. This opens the door to double spending. This was exactly the att…

The problem I think is that there are 25 cryptocurrencies bigger than it. Particularly with its form of mining, it's trivially easy for say a big player in the 10th largest currency to shift their mining power to a smaller one like Bitcoin Gold, overpowering everything else.

Normally the non-51% attack argument is that anyone who invests enough in 51% of the infrastructure and has sufficient coins to profit from double-spending, is very unlikely to do so because it would render the coins and mining equipment worthless or at least worth less than the investment had cost.

That'd be true for bitcoin, but not for a GPU-mined 26th largest cryptocurrency. You can completely destroy it, cash out and use your equipment elsewhere on coins in which people still have faith.

Re: Bitcoin Gold Hit by Double Spend Attack, Exchanges Lose Millions

#236

Post by dustingetz »

jhpriestley wrote: post #83

When Bitcoin was running up to $20,000, I tried to analyze the system and come to a personal conclusion about its equilibrium value, because I didn't want to miss out if it really was the currency of the future. I ended up not investing, because of the possibility of a double-spend attack. I think that cryptocurrency enthusiasts are seriously underestimating the importance of double-spending attacks to the economics…

2nd and 3rd gen blockchain tech is not vulnerable to double-spend attack, i believe. Only the legacy chains (Bitcoin, Litecoin etc) are

Re: Bitcoin Gold Hit by Double Spend Attack, Exchanges Lose Millions

#237

Post by hndamien »

CydeWeys wrote: post #222
hndamien wrote: post #204

Earlier quoted context omitted.

But they also require observation for cheating because time matters in the execution of contract settlement when you have bad actors. It is still trustless though.

You've always had to protect against cheating though; what's changed? The standard advice from as far back as I can remember is to wait six confirmations on transactions, more for big transactions, and 120 for freshly minted coins.

The difference here is you can just wait long and you are good. In the case of lightning network there is a time limit. If you wait too long and don't notice what happened/ is happening you are cooked.

Re: Bitcoin Gold Hit by Double Spend Attack, Exchanges Lose Millions

#238

Post by mortdeus »

tehsauce wrote: post #110
tlarkworthy wrote: post #92

Earlier quoted context omitted.

I think the argument is that by doing a 51% attack you undermine the market value so you never get the rewards. This makes sense, but only for the leading crypto coin. As we see here today, you can 51% attack smaller coins, which should imply an increase in the value of Bitcoin from consolidation.

The spooky thing that this made me realize, is that if anyone did find a vulnerability in bitcoin (or any cryptocurrency) is that they would have a greater incentive to only slowly leech off the system, because they will be able to siphon out much more over time than if everyone panics over security. The weapon is no good unless it's secret.

What about state level actors, say the NSA, that consider bitcoin supplanting the US dollar as the standard medium of international currency exchange a huge threat to the world economy? (or at least their ability to control it)

I think people need to be concerned that Governments, at any point of time, with their incomprehensibly huge computation power, can use it to crush bitcoin. Not only that but they can pass laws that allow them to forcibly seize the fattest wallets. Which ultimately ensure's that the Government can, behind the scenes, kick the scaffolding out from beneath us. All I see right now is state level actors experimenting in this regard, because seriously who single handedly has the computation power to take control of these cryptocurrency's if its not the government or a company like Google?

Re: Bitcoin Gold Hit by Double Spend Attack, Exchanges Lose Millions

#239

Post by slededit »

paulgb wrote: post #226
slededit wrote: post #190

Earlier quoted context omitted.

Fort Knox has an entire military base to secure it. That alone would use up a good chunk of your few hundred million dollar budget. I think you are vastly underestimating the cost in supporting our current financial system.

These have to do with storing something of value, they aren't inherent to gold. People are already storing Bitcoin keys in physical vaults: https://www.bloomberg.com/news/articles/2018-05-09/bunkers-f...

The global financial system is interconnected. Fast transactions can happen because counter party risk is removed by a government backstop. In effect you can't have Visa without a "risk free" store of value. Vaults such as Fort Knox are a part of that system.

In the case of bitcoin they aren't inherently necessary to the function of the system, although with the risk of hacks you can make the case for them.

Re: Bitcoin Gold Hit by Double Spend Attack, Exchanges Lose Millions

#240

Post by Rodyland »

hinkley wrote: post #233
XR0CSWV3h3kZWg wrote: post #6

more details here: https://forum.bitcoingold.org/t/double-spend-attack-on-excha... Bitcoin gold was a fork to try and decentralize mining. It changed to a proof of work that is supposed to be ASIC resistant. It looks like the typical situation is mining by GPU for equihash (BTG PoW). BTG hashrate is at ~30MH/s at the moment, where Zcash's hashrate is at ~486MH/s. I don't have the numbers off hand, but it'd be interes…

Not every distributed consensus algorithm is happy with 51%. If you increased the minimum to 60% you’d increase the number of machines the attacker requires by 50%. If 100 machines play fair, >50% requires 101 evil machines, but >60% requires 151 evil machines.

I think you're misunderstanding the meaning behind a 51% attack?

An honest network participant will accept the chain with the largest accumulated proof of work. This is necessary to resolve forks of the chain, which are a natural occurrence.

A 51% attack means that the attacker can create a chain with more work than the rest of the network.

The idea that you can say "we require 60%" makes no sense by itself - you have to say what you actually mean in the context of a competitive and adversarial distributed proof of work blockchain network...

Maybe you have some ideas how to avoid history-rewriting attacks, in which case you should write a white-paper and launch your own sh1tcoin or ICO (only half joking).

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