51% attack

[right wing authoritarian]

Would this just only fork the chain which would leave the rest of us happy bitcoiners bitcoining as usual after the temporary disruption?

[1714302119]

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[apsvinet]

According to Sotoshi's white paper, it seems that a 51% attack would only disrupt current transactions but not affect the previous blocks.

Where can one find this?

I think he means the original paper by Satoshi https://bitcoin.org/bitcoin.pdf
However I can't find any explicit mentioning of the 51% attack in it.

Hm me neither, that's what I thought he referred to as well.

[kthejung]

According to Sotoshi's white paper, it seems that a 51% attack would only disrupt current transactions but not affect the previous blocks.

Where can one find this?

I think he means the original paper by Satoshi https://bitcoin.org/bitcoin.pdf
However I can't find any explicit mentioning of the 51% attack in it.

Hm me neither, that's what I thought he referred to as well.

Under "Calculations" section of bitcoin.pdf

quote:
-"We consider the scenario of an attacker trying to generate an alternate chain faster than the honest
chain. Even if this is accomplished, it does not throw the system open to arbitrary changes, such
as creating value out of thin air or taking money that never belonged to the attacker. Nodes are
not going to accept an invalid transaction as payment, and honest nodes will never accept a block
containing them. An attacker can only try to change one of his own transactions to take back
money he recently spent"
end quote.

To generate an alternate chain faster than the honest chain would mean that the attacker would have 51% or greater control of network.  How else would someone generate a chain faster than the main chain?

[Meuh6879]

We consider the scenario of an attacker trying to generate an alternate chain faster than the honest
chain.

P2Pool create already this system ... but have "only" 160TH/s.
and the overhead, CPU, stale and Dead-On-Arrival ... is high, too.

[apsvinet]

According to Sotoshi's white paper, it seems that a 51% attack would only disrupt current transactions but not affect the previous blocks.

Where can one find this?

I think he means the original paper by Satoshi https://bitcoin.org/bitcoin.pdf
However I can't find any explicit mentioning of the 51% attack in it.

Hm me neither, that's what I thought he referred to as well.

Under "Calculations" section of bitcoin.pdf

quote:
-"We consider the scenario of an attacker trying to generate an alternate chain faster than the honest
chain. Even if this is accomplished, it does not throw the system open to arbitrary changes, such
as creating value out of thin air or taking money that never belonged to the attacker. Nodes are
not going to accept an invalid transaction as payment, and honest nodes will never accept a block
containing them. An attacker can only try to change one of his own transactions to take back
money he recently spent"
end quote.

To generate an alternate chain faster than the honest chain would mean that the attacker would have 51% or greater control of network.  How else would someone generate a chain faster than the main chain?

No that seems to make sense. Doesn't seem to be that big of a deal if this is true, however we can't know if he missed something until someone actually tries and succeeds.

[Brangdon]

[quoting Satoshi] An attacker can only try to change one of his own transactions to take back
money he recently spent"

The problem is that we won't know which transactions are theirs, so every transaction becomes suspect even if only a small number of transactions are directly affected.

[billysweird]

https://www.youtube.com/watch?v=bi2thGzzNSs

seems like it's alot easier then some people claimed...

Oh no, hope it doesn't happen

[sshapiroNJ]

can you say in a short way what is in this video about?

[jonald_fyookball]

A 51% attack would NOT necessarily mean everyone would switch to litecoin. 

Instead, miners would just leave those corrupted pools and
join new ones not under the control of the dark lord of the sith.

And bitcoin lives on.

[devphp]

A 51% attack would NOT necessarily mean everyone would switch to litecoin. 

Instead, miners would just leave those corrupted pools and
join new ones not under the control of the dark lord of the sith.

And bitcoin lives on.

How hard would it be for a powerful entity to take control of the 3-4 largest pools to completely paralyze the network? Not very hard I would say if that entity has enough political will to do that.

Now, this would be much harder to do, if at all possible, with such a coin as Myriadcoin or NXT, as they have enough protection by design not to fall victim to such an event.

[Superluz]

part 2

https://www.youtube.com/watch?v=Kjtgp5h-jEY

[Brangdon]

can you say in a short way what is in this video about?

It's a long-winded estimation of how much it would cost to acquire 51% of Bitcoin's hash power. With some explanation of why it matters and where the numbers come from.

[apsvinet]

part 2

https://www.youtube.com/watch?v=Kjtgp5h-jEY

Ah, been waiting for this one, thank you!

[Brangdon]

Part 2 is more interesting. I hadn't realised that if a 51% miner secret mines empty blocks for 6 hours and then releases them, that would reset all transactions in those 6 hours back to zero confirmations. That would allow double-spends on all those transactions to be attempted, not by the miner (who doesn't know the private keys) but by whoever initiated the original transactions. The miner could then continue mining in public, accepting transactions, but given preference to the double-spends. Basically it would be a lot worse than Bitcoin being offline for 6 hours.

The idea that this could be countered by looking for long chains of empty blocks is surely wrong. The attacker could fill them with their own, dummy transactions.

I'm not so sure about his claim that the miner could be mostly honest, and accept 99% of transactions but exclude ones for Overstock. That kind of targeted attack would require knowing which transactions were Overstock's.

[jonald_fyookball]

A 51% attack would NOT necessarily mean everyone would switch to litecoin. 

Instead, miners would just leave those corrupted pools and
join new ones not under the control of the dark lord of the sith.

And bitcoin lives on.

How hard would it be for a powerful entity to take control of the 3-4 largest pools to completely paralyze the network? Not very hard I would say if that entity has enough political will to do that.

Now, this would be much harder to do, if at all possible, with such a coin as Myriadcoin or NXT, as they have enough protection by design not to fall victim to such an event.

Yes but it could only get control for a short time before everyone realized what is happening and changes pools.  It would be a huge disruption but not the end of bitcoin.

[devphp]

Yes but it could only get control for a short time before everyone realized what is happening and changes pools.  It would be a huge disruption but not the end of bitcoin.

Hm, do you think that other pools they run to would continue to work just fine? I mean it won't take a long time to identify other pools' operators and if there is a decision to shut the network down, it will be shut down. The chances of this need to be eliminated by design, which is what Bitcoin simply doesn't have. If we put our collective heads in the sand and pretend the problem doesn't exist, well, some day it might kick us in the butt.

[Robert Paulson]

Yes but it could only get control for a short time before everyone realized what is happening and changes pools.  It would be a huge disruption but not the end of bitcoin.

Hm, do you think that other pools they run to would continue to work just fine? I mean it won't take a long time to identify other pools' operators and if there is a decision to shut the network down, it will be shut down. The chances of this need to be eliminated by design, which is what Bitcoin simply doesn't have. If we put our collective heads in the sand and pretend the problem doesn't exist, well, some day it might kick us in the butt.

pools are distributed across different countries, there would have to be a global agreement in all the countries involved to shut all the pool's down.
even if for some reason all the world governments agree to shut pools down its always possible to start a pool as a TOR hidden service and let it operate like silkroad.

[jonald_fyookball]

i agree might be good to proactively think about it.  probably people have.
im just saying, trying to shutdown bitcoin by attacking mining pools
won't work because it is easy for any miner to switch pools quickly.

[devphp]

i agree might be good to proactively think about it.  probably people have.
im just saying, trying to shutdown bitcoin by attacking mining pools
won't work because it is easy for any miner to switch pools quickly.

The problem is, if the big mining farms were shut down (not the pools), then the hashrate would drop several fold, which means new blocks would be solved who knows how often, perhaps one block per day. So it's not that easy to switch, I mean yeah, the remaining small fish miners can switch to other pools, but the network would still be paralyzed.

If bitcoin developers actually changed the code so that the difficulty is recalculated after each block, the way they do in Dogecoin now, this wouldn't be an issue. If hashrate drops a lot, the difficulty quickly drops too, and the blocks keep being solved as if nothing happened, but when you have difficulty readjustment every 2000 blocks like it's set up in bitcoin now, this would be hell of a nightmare to wait, what, months perhaps, for next difficulty readjustment, it can get crazy.

[jonald_fyookball]

Pools are way more concentrated than actual mining farms.  I think shutting down some big farms won't have a huge impact on the network.  Even if the network were cut in HALF, it would be readjusted in less than a month.