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Ghash.io very close to 51% of bitcoin pool

bitcointalk.org

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Re: Ghash.io very close to 51% of bitcoin pool

#31
post #18

Earlier quoted context omitted.

None of their miners have to collude in any way; scary stuff is entirely up to the pool operator to execute and the miners won't even know that they're helping until it has happened. At this point it's tempting to consider just mining for this pool as collusion, however. GHash.io have been known to abuse their mining power to double-spend already. Miners are not showing much will to leave for other pools, however. It…

> It's a dire situation. Hoards of people dump insane amounts of money into a new, unproven and unstable currency technology. What could go wrong?

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Re: Ghash.io very close to 51% of bitcoin pool

#32

Could someone with knowledge of Bitcoin explain what happens when a share of the pool hits 51%? Is this dangerous in some way? Edit: Thanks to those who took the time to explain. Very interesting.

The pool operators could launch 'double spend' attacks. Essentially with > 50% of the hashing power, a bad operator is able to generate a chain faster than the rest of the network. They can hold back this longer chain in secret, execute some transactions on the honest chain, then broadcast their chain (which doesn't have those transactions included) to the network. The network will use the evil chain since it is the…

There are rumours that that double-spend attacks have already been tried or experimented with by someone linked to the Ghash.io pool: https://bitcointalk.org/index.php?topic=327767.0

Re: Ghash.io very close to 51% of bitcoin pool

#33
Can someone please explain what Ghash.io and BTCGuild are? I have checked both homepages and subpages, but still don't understand what it is. Ghash.io wants me to download a binary, the other one talks about a "mining pool". Can't figure what that even means..

Disclaimer: Bitcoin noob here

Re: Ghash.io very close to 51% of bitcoin pool

#34

Could someone with knowledge of Bitcoin explain what happens when a share of the pool hits 51%? Is this dangerous in some way? Edit: Thanks to those who took the time to explain. Very interesting.

Here you go:

http://bitcoin.stackexchange.com/questions/658/what-can-an-a...

http://learncryptography.com/51-attack/

Re: Ghash.io very close to 51% of bitcoin pool

#35

If a pool has control of >50% of the hashing power, it means that they could do damaging things to the Bitcoin network as far as I understand. People will explain that it's not in the pools interest to do this, but it's missing the point. The pool is now a potential weapon, with a very small number of people in control. This means they are now a potential weapon against Bitcoin, and if someone external wanted to hurt…

Malicious attackers or disgruntled employees could also gain access to the pool and do nasty things.

Re: Ghash.io very close to 51% of bitcoin pool

#36
post #18

Earlier quoted context omitted.

None of their miners have to collude in any way; scary stuff is entirely up to the pool operator to execute and the miners won't even know that they're helping until it has happened. At this point it's tempting to consider just mining for this pool as collusion, however. GHash.io have been known to abuse their mining power to double-spend already. Miners are not showing much will to leave for other pools, however. It…

> It's a dire situation. Hoards of people dump insane amounts of money into a new, unproven and unstable currency technology. What could go wrong?

Mining power can centralize -- there are some solutions to this. One of them is https://en.bitcoin.it/wiki/P2Pool

Re: Ghash.io very close to 51% of bitcoin pool

#37

If you check https://blockchain.info/pools Ghash.io is back down to 39% of blocks created, which is still big, but not as scary. A good explanation is due to the random variation in the who the block is a awarded to.

The chart you link is over the past 4 days. In the past 24 hours, they are still at 41%. Although I agree there's bound to be a bit of random fluctuation.

It's dropping nicely, down to 39% over last 24 hours.

Re: Ghash.io very close to 51% of bitcoin pool

#38
post #10

Could someone with knowledge of Bitcoin explain what happens when a share of the pool hits 51%? Is this dangerous in some way? Edit: Thanks to those who took the time to explain. Very interesting.

My understanding is that if one entity controls 51% of the network, they can push arbitrary modifications into the block chain. In effect, they can do whatever they want.

That is not correct, the consequences are still very bad.

What can you do with 51%? You can (theoretically) revert a transaction that has been confirmed, by mining blocks attached to a prior point in the blockchain and getting a longer chain than the rest of the network.

What can't you do? You can't spend someone's coins when you never had their private key to begin with. Making a transaction is an act of "signing" and public-private key cryptography is not dependent on the block chain style technique for sending messages, only for making sure that they got through and maintaining them as a ledger.

You can probably single out arbitrary transactions and make sure that those are the ones that are reversed -- your transactions, so the evidence would point back to you, and whomever accepted your bitcoins as payment for something, would potentially know it was you who wronged them.

You could also decline to single out a transaction, just reversing all transactions after a given block and starting a "new life" for all the people who spent their coins after that. When you refused to re-sign the transactions that you made, you would then out yourself.

All of this is fairly academic since the person in charge of 51% of the hash power (GHash.io owner/operator) is a known actor, the hordes have not trusted him/them anonymously, and it turns out that miners have the least incentive to perform this kind of attack, since you lose an amount of revenue equal to the contents of the number of (your) solved blocks that you reversed. They would be more likely in my opinion to accept hashes and proof of work, but then renege and refuse payment to their miners, since this is really a less sophisticated attack and either way you should lose all of your credibility as a pool operator when you are discovered.

Re: Ghash.io very close to 51% of bitcoin pool

#39

In 2011, Jed McCaleb pointed out that bitcoin mining pools can collude. So in fact, Bitcoin is based on trust ... it is based on trust that mining pools are not colluding against you. His idea was to make this trust explicit. And that's the birth of Ripple. Ripple's consensus process is predicated on trust that other entities are not colluding against you. The Ripple protocol is not subject to the 51% attack that Bit…

Nice try Phil. Please get your Ripple propaganda off of HN. Ripple currency, XRP, is magicked up by Ripple Corp which owns nearly all of it and is the purest form of a pyramid scheme.

Re: Ghash.io very close to 51% of bitcoin pool

#40

There's no safety even if GHash.io is below 50%. How can we tell that GHash.io and BTCGuild aren't already colluding? They have 61% between them.

Even without that collusion, if you control 40% you still have a high probability of pulling off a double-spend attack. My recollection (sorry, I don't have a link, so I might be wrong) is that someone somehow associated with GHash.io already pulled something like this off when they were still below 30%
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