Topic: 51% attack - page 2. (Read 5169 times)

In addition to what DannyHamilton said, you don't have one of these because it's not a valid concept.

Correct.

And if you don't have a majority of the hash power in the network, and the other miners don't implement your particular exact ruleset, then your chain will never be longer than the consensus chain.  Therefore, every block that you mine will be a waste of your hash power.

Since every other miner faces this same disincentive, the only financially logical thing for you or any other miner to do is to accept the protocol-valid blocks that you receive and mine blocks that follow them.

I'm confused with what exactly your position is now. 

If I as a miner have a technique to reliably detect malicious blocks created by double-spend services, and if I choose not to build upon those blocks, then this does not represent a change to the protocol IMO.  I am expressing my view of the legitimate chain with my hash power. 

Do you disagree?

I think this is one of the problems of Bitcoin which makes it vulnerable to a problems in a 51% attack.

See my thoughts here:

https://bitcointalksearch.org/topic/transaction-inclusion-and-exclusion-582386

Miners choosing to collude is one of the potential failure cases of Bitcoin.

The protocol should not be changed to make this collusion easier to engineer, or more difficult to detect.

It sounds like we agree then.  If miners establish techniques to detect malicious blocks, they are free to choose not to build upon them. 

Miners are free to include or exclude any transactions in their blocks that they wish, and are also free to chose which valid block to extend the chain from.

The proof of work algorithm is the process of determining which chain is canonical.

Yes.  You are correct.  It is coin confiscation. 

What is your opinion on #1?

There's no slope - that's exactly what it is.

Spending outputs without satisfying their scripts is a fundamental perversion of the network - it's like building a calculator that sometimes will declare that 2+2=5 when a committee decides that the result of some equation "doesn't deserve" to be 4.

Here are Mike's suggestions:


I dislike #2 because I see it as a slippery slope to coin confiscation, and I believe this requires changes to the source code.

#1 seems like something that can accomplished now without any changes to the bitcoin code.  Basically, it is a way for honest miners to come to consensus on which blocks were created by malicious double-spend services and agree not to build on top of them.  I think this idea may be worth evaluating in more detail. 

Mike Hearn is trying to enshrine the 51% attack into the protocol such that a majority cartel of miners can confiscate the generation transaction (just that, for now) of any other miner they want.

http://sourceforge.net/p/bitcoin/mailman/message/32258096/

Correct. With POS coins the amount of $ needed to do a 51% attack goes up exponentially.

Although it's true that PoS is much more protected, there is one PoW coin - Myriadcoin, that is technically considerably more secure than other PoW coins. Attacker would have to gain 51% hashpower in more than one (probably all 5) independant algos, otherwise, the network would still run without interruption.

Here, what a user with 51% can do and not do:
https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_computing_power

Oh, I never thought of that. So the 51% attack is an issue. We need to trust the pool operators. I hope P2P pools gain in hashing power. Does anyone know how much they do nowerdays?



No altcoin with POW is immune against that 51%. Not matter whether GPU or CPU mining. So POS coins could be an alternative.


You think, someone has that capital so buy such mining equipemt and is not capable to start mining from several different IPs?

An explosion would be great at Knc's farm.

We are talking in 2 threads simulateously, lol.  I explained how even the extremely unlikely event of a sustained 51% attack is not that great a threat here: https://bitcointalksearch.org/topic/m.6364725 .  

The value of bitcoin comes from our community's shared agreement that the blockchain ledger is legitimate.  As long as this is the case, bitcoin will live on.  

It could be part of the defense budget, who knows...maybe JP Morgan just decides to do it...or HSBC...or both... I have no idea.  I trust government and banks about as far as I can throw them.  My point is, lets make as technically infeasible as possible.  And right now its technically feasible. 

And I would argue that a sustained 51% attack (mining monopoly) could utterly destroy confidence in Bitcoin if the monopoly was malicious.

How would a government do this, Jonald?  Would Congress pass the "51% Attack Bitcoin Bill" authorizing spending of $0.5 billion?  Do you think such a bill would pass, let alone receive popular support?  

If your answer is that a small-subset of government would do it secretly and in private, then why would they bother 51% attacking bitcoin?  Why not just pocket all the mined bitcoins if they knew they wouldn't get caught.  "Oops, I guess it didn't work.  Good thing the tax payers paid for these bitcoin miners.  Hey, what happened to those mined coins?"

And it's not like the 51% attack would kill bitcoin anyways.  It would just be annoying for a while (and a bunch of people would probably panic sell).  

As for banks, if they thought bitcoin was such a threat that it was worth spending half a billion just to annoy the network for a while, then why not invest half a billion dollars into purchasing bitcoin for cheap, perhaps from a bankrupt exchange, co-opt the system, and pump the price to the moon?  The most talented people at the big banks are well situated to profit from bitcoin.

That all being said, I do support efforts to decentralize mining!

Interesting topic. I'd just throw into the mix the possibility or targeted attacks on the infrastructure of the largest farms. If the power supplies of the top five farms suffered a coordinated global attack what percentage of the network could be taken down? If it were a significant amount then it would be worth doing just before a 51% attack as the hardware then needed to get to 51% of the reduced network would be significantly smaller.

Would such a 51% attack fail once the farms got their power back up and that 51% became 40%? If so a more permanent shut-down could attempted eg fire/explosive attack on the largest farms.

The goal would be to destroy Bitcoin. I don't think they'd bother now, but as it becomes more successful it becomes more of a target, until (in my view) a large attack is inevitable.

Why do you think Bitcoin could be revived afterwards? Why would there even be an "afterwards"? Once they've bought the hardware, they can continue the attack indefinitely, for only the cost of electricity. They don't even need to run it continuously. They could, at random times, release a few hours of privately mined forked chain. That would be enough to make the system almost unusable.

By "the government", are you thinking America is the only threat? What about terrorists? As an attack on financial infrastructure, it would have similar symbolism to the 9/11 attack on the World Trade Centre. (How can you get more "world trade" than Bitcoin?) It would avoid the negative publicity of civilian deaths, and avoid the need for them to risk their own deaths. Alternatively, Russia might do it in retaliation for economic sanctions imposed on them, eg over Ukraine. Or China, or any country that has currency controls. Or a private bank. HSBC recently paid over $4b in fines; $100m would be easily affordable to them.

ASICs will plateau, but the block-chain reward will also decrease, and I don't think transaction fees will rise quickly enough to compensate, and nor will the volume of transactions. So we may find that existing miners keep going, because their ASICs are good for nothing else, but few new miners will want to get involved because they'll never cover their capital costs. And while the attacker is attacking, the miners could be mining zero blocks.