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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

#171

Post by droidist2 »

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.

But what if someone else also finds the vulnerability? You can't be sure they'll also act slowly. It's like a game theory dilemma.

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

#172

Post by 384243423 »

alttab wrote: post #161
vntok wrote: post #140

Earlier quoted context omitted.

No it would not. Finding a BTC double spend attack vector would be like finding a 0-day: good and maybe even profitable up until fixed, which would take hours, days at most. Have 0-days destroyed Microsoft, Android, Firefox, Electron or Chrome?

So it's ok if your currency becomes unreliable for many hours? It would immediately negate the trust of what happened during that period of time, affecting the trust of any balance in participating addresses.

We still use USD after 2008.

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

#173

Post by oh_sigh »

XR0CSWV3h3kZWg wrote: post #141
oh_sigh wrote: post #130

Earlier quoted context omitted.

Even finding a single double spend attack that only double-spends 1 satoshi would be enough to destroy bitcoin.

You won't really be able to process tx that low, you'll need to pay a tx fee proprtionate to the number of bytes. 1 satoshi per byte is a good rule of thumb for a very cheap tx. It takes more than 1 byte to describe one satoshi, so you can't get your tx to propagate.

Theoretically the attacker could also be picking up 0-fee transactions, but my intent was to really say this: it doesn't matter how small a double spend is - the ramifications for the network are the same.

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

#174

Post by xur17 »

icook wrote: post #165
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…

I was curious about the cost as well, so I ran some rough numbers. 417.5 BTC/GH/day for equihash if you're renting from nicehash [1]. Block interval 10 minutes [2]. 144 blocks per day target yields 0.0869 BTC/block, so cost of the 22 block reversal was ~1.91 BTC, or roughly $15k. I'm curious if this was done as one large deposit, or many smaller deposits. I've imagined a system where block confirmations required are…

I'm curious how many other smaller PoW currencies are vulnerable to something like this.

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

#175

Post by cesarb »

tedunangst wrote: post #18
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…

> If the exchange is aware of the attack, they may also freeze his account, so that all the funds will be locked inside the Exchange. A failed 21 block attack performed with a 10,000 BTG deposit where the Exchange freezes the account in time will result in a 10,262.5 BTG loss for the attacker. (From link.) That sounds problematic. If I deposited coins and the exchange determined I was attacking them (how does that wo…

Not only that, but also an attacker can wait until the money is "safe" outside the exchange before revealing the attack. If the attacker really has more than half of the hash rate, there's no time limit; the malicious chain will always be longer than the innocent one.

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

#176

Post by doorbumper »

alttab wrote: post #161
vntok wrote: post #140

Earlier quoted context omitted.

No it would not. Finding a BTC double spend attack vector would be like finding a 0-day: good and maybe even profitable up until fixed, which would take hours, days at most. Have 0-days destroyed Microsoft, Android, Firefox, Electron or Chrome?

So it's ok if your currency becomes unreliable for many hours? It would immediately negate the trust of what happened during that period of time, affecting the trust of any balance in participating addresses.

Bitcoin hasn't been useful as a currency for a long time. I don't think that's a good measure for determining how an event might affect bitcoin price.

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

#177

Post by EpicEng »

alttab wrote: post #161
vntok wrote: post #140

Earlier quoted context omitted.

No it would not. Finding a BTC double spend attack vector would be like finding a 0-day: good and maybe even profitable up until fixed, which would take hours, days at most. Have 0-days destroyed Microsoft, Android, Firefox, Electron or Chrome?

So it's ok if your currency becomes unreliable for many hours? It would immediately negate the trust of what happened during that period of time, affecting the trust of any balance in participating addresses.

This has already happened multiple times to BTC and it's still around. BTC is not a currency; that train left long ago.

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

#178

Post by bo1024 »

thaumasiotes wrote: post #155
bo1024 wrote: post #145

Earlier quoted context omitted.

Those are some really great and interesting points. However, I think there is a resource you didn't mention that combats such attacks: time. If I'm a vendor, e.g. I pay cash for bitcoin, then I can tune the amount of time the transaction is held in limbo or escrow based on the vulnerability of the network. For instance, I can decide not to finalize the transaction until I see a chain with 12 new blocks added after th…

> I see Bitcoin moving toward an intermediary system where you have a "Bitcoin balance" with a "Bitcoin bank" that allows you to make immediate transactions and takes on the risk and time delay of settling these transactions on the blockchain over the course of the next day or two. How would this system differ from an ordinary bank in the system we have now?

Right -- it would start looking like the traditional banking system, just sitting over Bitcoin rather than state-sponsored currency. (Not saying whether this is a desirable direction or not, just what I would expect to happen.)

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

#179

Post by XR0CSWV3h3kZWg »

icook wrote: post #165
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…

I was curious about the cost as well, so I ran some rough numbers. 417.5 BTC/GH/day for equihash if you're renting from nicehash [1]. Block interval 10 minutes [2]. 144 blocks per day target yields 0.0869 BTC/block, so cost of the 22 block reversal was ~1.91 BTC, or roughly $15k. I'm curious if this was done as one large deposit, or many smaller deposits. I've imagined a system where block confirmations required are…

As the space matures I'd love to see a company that offers double spend insurance for a given tx.

For example changes could wait for 10 minutes worth of blocks then request a quote for double spend insurance. The company evaluates the probability of a double spend and maybe even has a couple standing contracts with rentable hashing power to be able to target smaller PoW chains and prevent any double spend attack.

There are lots of interesting and cool problems to be solved in evaluating the safety of a given tx. Unfortunately I don't know if the space is mature enough that exchanges would actually use the service.

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