Bitcoin Forum

I have noticed a lot lately that many people have been talking about the 51%. What exactly is everyone talking about? I have yet to find a proper explanation.

I only had to google "51% explained" to find this, not even the word Bitcoin.

https://bitcointalk.org/index.php?topic=559217.0

And it's on this forum.

You can find the info on bitcoin wiki. :)
https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_computing_power

I'm also going to say right now:

Those still going on about the 51% have no evidence to back them. Multiple charts show that GHash.io (The pool nearing 51%) Is now below 35%.

Ironically, everyone's freaking out that GHash is at 33%. Because the rise from 20% can just go unnoticed and then everyone cares once they near 51%...  ::)

But the 51% paranoia is starting to dissapate. It would be a good idea to educate yourself on the info about it, however, so check out some of the links or google "51% attack".

Ghash.io has about ~35% of total network hashrate now, but their share was as high as 48% a week ago AFAIK.

http://www.coindesk.com/bitfury-pulls-power-ghash-community-uproar/

If you own 51% of the network, you can fork the network and reverse any transaction even when they have 1 confirmation. They can successfully attack the network since they own more than half of the network. They can prevent some transactions from getting confirmed and other pools from getting any blocks. Ghash.io had 51% of the network for some time.

Thanks ranochigo for good explain

There are also good video's on youtube - search Bitcoin network - Explaining this in detail. But for now it's not a big threat. Some people might want to start a panic sell, with 51% for them to buy some cheaper bitcoins, when the price goes down.  ;)

Miners just change pools, before this happens. But Ghash.io has it's own operation doing mining, and it's growing.

Don't worry, problem is solved now.
Current situation:
Ghash.io 31%
BTC Guild 16%
Discus Fish 16%
Unknown 10%.

https://i.imgur.com/hxmGq2T.png

Solved? 3 pools operate 90% of the networking hashing power. That is incredibly centralized. And 51% is NOT necessary to carry out a double spend attack. People need to wise up...

3 pools operate 90% of the networking hashing power? Where did you get that from?
And what I meant is things are now much better if we compare to that what it was couple days ago.
But yeah we still need to decentralize more.

True, I obviously glossed over the numbers to get 90% there. My bad. :)

I just get frustrated with the attitude that anything has been "solved" by Ghash dropping 15%. This will only continue to happen. And it isn't the first time either. :)

I have to agree, last time I looked it was higher than 40% {I think 46%} It would be counter productive to try to destroy the cow, that produce the milk.

That is why, I think most miners, will do the right thing, and move to another pool, when 51% are reached.

What are you going to mine, if what you are doing, is destroying your currency? {Well reputation anyways} The pro fiat people will have a field day, if this happens, and they would have another reason to bash BTC down.  ???

But the answer is not simply moving to another (centralized) pool. Decentralized mining is possible, and there is no reason for such large segments of the mining economy to operate in this manner.

So is it true that even if a pool didn't have 51%, they could still double spend? How does that work?

I have understood it like that, if same pool gets 2 blocks in row it can double spend etc.
So more % that pool has easier it is.

I see, so it is a probability thing. So even with 20 or 30%, a pool could get lucky and get a few blocks in a row and do a double spend?

Yep, but as they gain hashpower the chances of the spend working increase huge.  Any large pool could potentially be a threat.  This is why we need more people using P2Pool

Yeah, but you have to start double spending at the first block and if you won't get second block in row you will get busted.
So you can't keep just trying to get 2 blocks in row.