Possible attack on bitcoin currency - page 2.

DannyHamilton

legendary

Activity: 3528

Merit: 4945

Quote from: sigmabe on December 04, 2017, 12:55:29 PM

I think, I'm the one with the "crazy" attack construction, so I think I should answer...

If it is crazy, why can't everybody give an easy logical reason, why it doesn't work.

It does work. It just isn't typically profitable. It is too difficult and expensive to gain control over enough hash power for a long enough amount of time to make the attack profitable. If you do have control over enough hash power to complete the attack, then in the majority of scenarios it is more profitable to engage cooperatively than maliciously.

Quote from: sigmabe on December 04, 2017, 12:55:29 PM

If it's obvious till "day 1" that we can do this attack, why isn't there anybody who does it?

Too expensive and difficult to accomplish. Less profitable than cooperative engagement.

sigmabe

newbie

Activity: 22

Merit: 0

I think, I'm the one with the "crazy" attack construction, so I think I should answer...

If it is crazy, why can't everybody give an easy logical reason, why it doesn't work. By the way, this here is less crazy than my construction and there are also papers dealing with this so called whale attack, look for example in https://www.cs.umd.edu/~gasarch/reupapers/bitcoin.pdf (suggested by Pieter Wuille on stackexchange)

If it's obvious till "day 1" that we can do this attack, why isn't there anybody who does it?

Syke

legendary

Activity: 3878

Merit: 1193

Old news since day 1. You can do anything once you have >50% of the hashpower.

https://en.bitcoin.it/wiki/Majority_attack

pebwindkraft

sr. member

Activity: 257

Merit: 343

I am asking myself, why this is the third question of this crazy construct within this week... coincidence?

So: why would the miners accept this? When they know, that afterwards the currency is out of value?
They can't even use the remaining hardware to mine other coins, cause they know, that history shows, when bitcoin goes down, all other currencies go down - and vice versa.
The incentive for the miners is not recognizable.

Besides that nobody knows, how many miners there are (yes, there are pools, but then what?), you would need +8billion to bribe the miners. 16 billion is the amount of newly generated bitcoins at a rate of 10.000 Euro/CHF/USD ...
To whom would go the transactions of this size? To an exchange? to a bank? Who would be your counter party? Who is going to loose the large amount, if you take "your" transaction back with the miners after 15 blocks?
I guess, nobody takes a risk, that is higher than everything else that have been seen before? An alien bank perhaps, that doesn't care, if they loose 16billion?

This is not an attack on bitcoin currency. This is an attack construction, which has no visible chance of getting realized. As such the headline and the word "attack" is highly misleading.

croraf

newbie

Activity: 10

Merit: 1

Attack example:

1. Make several large transactions in block X and wait for N blocks.

2. Contact more than 50% of miners (for example large pools) and bribe them in real life to make a fork just before block X and to mine on that fork for N blocks. So the old branch becomes obsolete.

3. For a bribe you offer reward that is several times (let's say 3x) larger than the reward for N blocks.

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Conclusion:
The parties you paid to in block X will be accept your payment (as you picked N as 15 for example), and after rewind you get your bitcoins back.

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