Is a 51% attack currently viable?

[Captimiz]

At the present, does any one company have the capabilities to do it?

[Iranus]

The closest anyone is to that right now is BITMAIN.  Speculation about how much of the hashrate they actually control is varied, but it's most likely well over 20%.  Also, a huge amount of the miners which they don't have mining at their pools are bought from them as they own a monopoly over the ASIC industry.

However, that doesn't mean they could actually pull off a 51% attack.  If it was noticeably getting close, people would probably avoid their services and prevent it like they did with ghash.io.

[Captimiz]

The closest anyone is to that right now is BITMAIN.  Speculation about how much of the hashrate they actually control is varied, but it's most likely well over 20%.  Also, a huge amount of the miners which they don't have mining at their pools are bought from them as they own a monopoly over the ASIC industry.

However, that doesn't mean they could actually pull off a 51% attack.  If it was noticeably getting close, people would probably avoid their services and prevent it like they did with ghash.io.

Would they avoid it even it gives them a lower profit/revenue?

[Xester]

No, the biggest threat would be Bitmain, especially with unpatched miners and antbleed. It's not a worry in my mind for now

I do agree with your statement that bitmain is the biggest threat today since I guess they have the most number of miners in the records. Even if they cannot possibly do a 51% attack but still they can do some 20% to 30% attack. But let us just hope that bitmain will not do that and if in case they will it will be a big trouble and problem on the blockchain.

[Iranus]

The closest anyone is to that right now is BITMAIN.  Speculation about how much of the hashrate they actually control is varied, but it's most likely well over 20%.  Also, a huge amount of the miners which they don't have mining at their pools are bought from them as they own a monopoly over the ASIC industry.

However, that doesn't mean they could actually pull off a 51% attack.  If it was noticeably getting close, people would probably avoid their services and prevent it like they did with ghash.io.

Would they avoid it even it gives them a lower profit/revenue?

It doesn't give them a lower profit/revenue.  Mining at Antpool for example isn't very profitable at all - actually, Antpool take 2.5% fees on miner revenues plus transaction fees.  In practice right now, that's well over 10% of miners' revenues!  All it gives them is the stability of mining at a big pool with less variance, but in reality they would be much better off mining at a small pool like Kanopool and if they were aware of that (which would happen if a 51% attack was nearing) they would do that.

It's very unlikely that it could happen really.

[lowbander80]

According to Gavin Bitcoin Unlimited could be preparing for an attack anytime and of course, you don't need 51% of the hashrate to accomplish it.You only need to make the original chain unworkable

[Slark]

Aside speculation that 51% attack can be done or not. Why would anyone Bitmain or other bad actors want to forceful split the network?

It would do no good to the BTC. I can see only negative consequences: price of BTC will crash (both chains), attack of this magnitude will undermine faith in bitcoin.

The only victor after forced BTC hard fork will be altcoins, mainly: Ethereum and Litecoin.

You can say that Ethereum did the same after the DAO fail, no it wasn't the same, ETH fork was done by high priests in power, Vitalik and ETH foundation not the usurpers.

[BTCLovingDude]

If it was noticeably getting close, people would probably avoid their services and prevent it like they did with ghash.io.

i don't remember anybody "preventing" anything with GHash.IO!
if my memory serves it was like this, GHash.io had more than 51% hashrate (it was about 60 i think this was a mistake) for sometime, and someday someone realized this and said oh shit there is a possibility of 51% attack!
then since they were a mining pool apart from having GHS themselves, some miners moved to other pools and the percentage came down.

edit: there you go, from 2014:

Confirmed https://blockchain.info/pools?timespan=24hrs

and just FYI, nothing bad ever happened. someone having high hash power doesn't mean they are going to double spend.

[ranochigo]

If it was noticeably getting close, people would probably avoid their services and prevent it like they did with ghash.io.

i don't remember anybody "preventing" anything with GHash.IO!

That's the main problem with the Bitcoin community. Ghash.io had the lowest fees and most miners find it troublesome to move their miners to another pool. Hence, nobody did anything and it took awhile for the hashrate to drop. Granted, they did publish a statement regarding it and their migratory measures.

In reality, the possibility of them executing a 51% attack is near to zero. They had datacenters, ASIC and an exchange. If they execute an attack, it would just be like committing suicide.
51% attack is always possible. The top mining pools can easily collaborate together and launch the attack. If you are referring to one owning the resources himself, its a no. It is way too expensive to accumulate that much hashrate.

There is currently no economic incentives to executing such an attack.

[YuginKadoya]

I don't think a company can really attack bitcoin that high, and I really think this is not viable right now and because of certain miners that are out of the pool bitmain is just 20% over that control, we will not see some bitcoin invasion action for now because the security of bitcoin is really impenetrable right now that is why we are safe!  

[BTCLovingDude]

If it was noticeably getting close, people would probably avoid their services and prevent it like they did with ghash.io.

i don't remember anybody "preventing" anything with GHash.IO!

That's the main problem with the Bitcoin community. Ghash.io had the lowest fees and most miners find it troublesome to move their miners to another pool. Hence, nobody did anything and it took awhile for the hashrate to drop. Granted, they did publish a statement regarding it and their migratory measures.

In reality, the possibility of them executing a 51% attack is near to zero. They had datacenters, ASIC and an exchange. If they execute an attack, it would just be like committing suicide.
51% attack is always possible. The top mining pools can easily collaborate together and launch the attack. If you are referring to one owning the resources himself, its a no. It is way too expensive to accumulate that much hashrate.

There is currently no economic incentives to executing such an attack.

the important thing about 51% attack is that this kind of attack should be performed for profit not just randomly making a fork and orphaning the 49%!

this means you spend a large amount of bitcoin (for example sell 1000BTC in block 40001) and take the fiat then with >51% start building on top of block 40000 instead and with having more hash power try making your new chain the longest chain and spend the 1000BTC again in the new block 40001.

the solution is not that complicated either. when you receive a large amount of bitcion (ie 1000BTC) you have to wait for more confirmation. in other words wait until it is deep enough. double spending after block 40002 is harder than after 40001 and 40003 even harder and 40010 even more and eventually it becomes practically impossible.

[lowbander80]

BTC.TOP Pool Operator Jiang Zhuoer

BTC.TOP is a relatively new Chinese mining pool. Launched in late 2016, the pool currently controls some 5 percent of hash power on the Bitcoin network.

BTC.TOP is operated by Jiang Zhuoer, a former employee at China Mobile in Shanghai. Much like several other small mining pools that have appeared over the past six months, BTC.TOP has been signaling support for Bitcoin Unlimited.

In an interview with Cryptocoins News in March, Zhuoer was the first who explicitly said a 51% attack against the original Bitcoin blockchain, if it were to survive after Bitcoin Unlimited miners split off, is on the table.

“We have prepared $100 million USD to kill the small fork of CoreCoin, no matter what [proof-of-work] algorithm, sha256 or scrypt or X11 or any other GPU algorithm,” he said, of course referring to the continuation of the current Bitcoin protocol as “CoreCoin.”

The different hash algorithms mentioned by Zhuoer refer to a potential proof-of-work algorithm change Bitcoin users could deploy if the chain is attacked; a “nuclear” defense some Bitcoin Core developers have suggested may be proposed in such a scenario. (Whether this should still be considered “Bitcoin” or yet another spinoff altcoin is subject to different debate.)

“Show me your money,” Zhuoer added. “We very much welcome a CoreCoin change to [proof of stake].”

(If no proof-of-work algorithm succeeds in deterring the attack, a proof-of-stake consensus algorithm — where coin holders rather than miners vote on the longest chain — may be an alternative solution. But since this is unproven and perhaps insecure, this seems highly unlikely

[Velkro]

At the present, does any one company have the capabilities to do it?

No, but sadly its not only danger. Imagine two companies alliance to do some %U#( to bitcoin. They could have 30% mining power and 20% mining power for example. But there could be 3  companies... with even lower hash rates but overall over 50%.
That is worrying a little bit.
But bitcoin is stronger than that.

[pereira4]

According to Gavin Bitcoin Unlimited could be preparing for an attack anytime and of course, you don't need 51% of the hashrate to accomplish it.You only need to make the original chain unworkable

In the case they attempt to get this suicidal then we will just switch PoW. But those are just all scare tactics, they will never resort to that. Sooner or later Buggy Unlimited will end up as irrelevant as XT and Classic. This is just a battle of pressure and sides are threatening each other with things that will not happen (UASF or 51% attack).
Or that's what I want to think, otherwise someone is really nuts or getting actively paid to attack BTC even if it means fatal damage.

[~Bitcoin~]

At the present, does any one company have the capabilities to do it?

I can't say it is impossible but it will cost so much for any company or person to conduct 51% attack on bitcoin network.
Right now bitcoin network is under massive spam transactions attack rather than 51% attack.

[ranochigo]

the important thing about 51% attack is that this kind of attack should be performed for profit not just randomly making a fork and orphaning the 49%!

this means you spend a large amount of bitcoin (for example sell 1000BTC in block 40001) and take the fiat then with >51% start building on top of block 40000 instead and with having more hash power try making your new chain the longest chain and spend the 1000BTC again in the new block 40001.

Note: There is no profit in this either.
Let me break it down for you:
You get the 1000BTC in fiat after 6+ confirmations. You mine 6+blocks and overtake everyone else, replacing the blocks. You get the reward, and you get more coins. However, merchants would most likely be alerted to this happening immediately and your Bitcoins are essentially useless; the ones you mined and the 1000BTC you double spent. Remember you have to consider about the money you spent to execute the attack.

^That's from my point of view, theres other perspectives to view it from but thats what you described.

the solution is not that complicated either. when you receive a large amount of bitcion (ie 1000BTC) you have to wait for more confirmation. in other words wait until it is deep enough. double spending after block 40002 is harder than after 40001 and 40003 even harder and 40010 even more and eventually it becomes practically impossible.

The problem is that the number of confirmations just makes things harder for those without 51% of hashpower. As long as they have 51% if the hashrate, they have nearly 100% chance of reversing anything after the checkpoint. Of course, no one would do this since its pointless.

[Ayers]

i looked around to understand better this 51% and how someone with huge hash can do it, but i see that he need first to make a large purchase with his private offline network which hold the 51% of the net, but by doing this large purchase the vendors can caught him and refuse the purchase or large exchange can stop the deposit or withdrawal of a very large sum that can be seen as a double spend

[Kprawn]

According to Gavin Bitcoin Unlimited could be preparing for an attack anytime and of course, you don't need 51% of the hashrate to accomplish it.You only need to make the original chain unworkable

Well back in the day, when  GHash.io was threatening to reach 51% ...Gavin said that there were counter measures that could be used to cancel

these attacks. {He never elaborated on what those was} He was Lead developer at the time and we took his word, without questioning what it

was. I think he hoped people would see that a 51% attack was counter productive and that people would leave these pools, if it became a threat.

[Nascor]

for Bitcoin, you'll need hardware worth $1,286,506,150.85 (one point two billion) to conduct a 51% attack

you can have a look at https://www.coingecko.com/en for the latest stats (check the Bitcoin row)

[btclaw]

Never going to happen, unless these etherium freaks pull it off.