Wish I could filter out the bitcoin news.
Ghash.io very close to 51% of bitcoin pool
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Re: Ghash.io very close to 51% of bitcoin pool
#12Could 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 longest, and since those transactions are not included, whoever accepted them beforehand has been ripped off.
It worries me that it's this hard to convince miners to leave a pool. If I wanted to kill Bitcoin and had a few million to spare, I'd open a pool with no fees PLUS a bonus of 1 or 2% from my own pocket. Good luck getting people to leave that pool.
Re: Ghash.io very close to 51% of bitcoin pool
#13If 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.
Re: Ghash.io very close to 51% of bitcoin pool
#14Ghash.io is "just" a pool. For them to do anything scary, all the members would need to collude, right? Or can the pool "direct" the mining in such a way that eg. double-spending can happen without the consent of individual miners?
Obviously, the second there's evidence of double spending or similar, any value of Bitcoin will disappear as dew on a summer morning and the value of all the ASIC gear with it - so there is a very strong incentive for each individual miner to refuse to participate.
Re: Ghash.io very close to 51% of bitcoin pool
#15Earlier quoted context omitted.
Can you explain what the threat is please?
http://www.cryptocoinsnews.com/2014/01/09/warning-ghash-io-n... ---The attacker can----: Reverse transactions that he sends while he’s in control Prevent some or all transactions from gaining any confirmations Prevent some or all other generators from getting any generations Double spend Bitcoins ---The attacker cannot---: Reverse other people’s transactions Prevent transactions from being sent at all (they’ll show a…
Thanks.
Re: Ghash.io very close to 51% of bitcoin pool
#16There'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.
Re: Ghash.io very close to 51% of bitcoin pool
#17Could 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.
> ...they can push arbitrary modifications into the block chain. In effect, they can do whatever they want.
No, since who holds what coin is defined by consensus, which has to stretch out of the mining pool. If they arbitrarily gave themselves coin, for example, then no other client would accept that they hold that.
See smtddr's reply for details of what they can and cannot do.
Re: Ghash.io very close to 51% of bitcoin pool
#18Ghash.io is "just" a pool. For them to do anything scary, all the members would need to collude, right? Or can the pool "direct" the mining in such a way that eg. double-spending can happen without the consent of individual miners? Obviously, the second there's evidence of double spending or similar, any value of Bitcoin will disappear as dew on a summer morning and the value of all the ASIC gear with it - so there i…
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's a dire situation.
Re: Ghash.io very close to 51% of bitcoin pool
#19In 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 Bitcoin is subject to. Making entries in the ledger has nothing to do with computational power.
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Link to the 2011 discussion that spawned Ripple: https://bitcointalk.org/index.php?topic=10193.msg146250#msg1...
EDIT: Adding a link explaining Ripple's consensus process for making changes to a shared ledger: https://ripple.com/wiki/Consensus
Re: Ghash.io very close to 51% of bitcoin pool
#20Could 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…
Who would want to kill bitcoin apart from governments? (They can just outlaw it.)
It's not possible to short it yet, is it?