Bitcoin Forum

Inverted 50% attack. And if half of the miners turn off their hardwares ?

Anyone could please explain the consequences of an attack like this ? (Intentionally made, of course).

I can imagine an never finalized next block.

I understand the inner workings of the Bitcoin network, and I think that an attack like this could be feasible at this time, with the increasing development of ASICs.

*** Sorry if the english is not perfect, i use the google translator.

Thanks.

Avage block time would be 20 minutes for a few weeks, then back to normal.

This, then our difficulty would be half and everyone would celebrate.

No doubt the perpetrators of this "attack" can expect much riches. I recommend they commence immediately.

It's hard to imagine this scenario.

Displacing this many miners on the network/getting that many to corroborate is unlikely.

The difficulty would still remain at X until readjustment so it's not like the remaining miners would profit that quickly and this would just increase the amount of time the other miners would have to be down.

That'd be great why not turn off 90% of the miners? ::)

What if 90% of us deleted our wallets!!!11!! A 90% attack!  :o   

Why? Higher the better.

Correction - miners would celebrate.  Those who prefer a secure network would be sad.

Also, previously uneconomic equipment (at the margins thereof) suddenly becomes worth mining with for the duration of the attack... the more of the network that goes down, the wider range of older equipment that becomes viable again. The peak hashrate will not be achievable (probably), but it could turn a 5 week difficulty adjust into, say, four and a half. (bitcoin) World doesn't end.

When I posted this question I was thinking more about the possibility of If at this moment there is already 50% control over the network, with some obscure government agency owning the majority of ASICs. I'm just imagining a scary scenario, not being a real thing.

I also still do not understood the real effects on the calculation of the difficulty when occurs an increase or decrease in hashpower on the whole network.

Assuming that 50% of hashpower is exactly 50% of the difficulty or have any variation  For example, with 50% more hashpower we have only 10% more on difficult or have an equivalence of 50% == 50% ?

Assuming that an increase in hashpower might (this is a question) rise exponentially the difficulty then when removing this extra hashpower no others will be able to meet the demand to complete a block, even in years ?

Thank you for the patience.

You can see the hash power distribution here: http://blockchain.info/pools

There is currently no single miner controlling 50% of the network or even close to it.

That is the beauty about bitcoin, decentralized ! No one must control 50 %+

50% then goes back online, making actual attacks a bit easier to pull off. Hyper50 Attack. We need more unique names for different theoretical attacks. I was thinking earlier, about the one-Satoshi dust transactions I'd guess are aimed at connecting addresses to an identity. I decided it should be called Dusty Taint Sniffing. ... Uh - what were we talking about?

No.  There is a perfect linear relationship between difficulty and hashrate.

If 50% of hashpower shut off (for whatever reason) then the time between blocks would rise to ~20 minutes and 0-4 weeks later the network would adjust and the time between blocks would fall back to 10 minutes.

If 75% of hashpower shut off (for whatever reason) then the time between blocks would rise to ~40 minutes and 0-16 weeks later the network would adjust and the time between blocks would fall back to 10 minutes.

If 90% of hashpower shut off (for whatever reason) then the time between blocks would rise to ~ 100 minutes and 0-20 weeks later the network would adjust and the time between blocks would fall to 25 minutes* and then 16 weeks later it would adjust again back to 10 minutes.

If 99% of hashpower shut off (for whatever reason) then the time between blocks would rise to ~1000 minutes and 0-200 weeks later the network would adjust and the time between blocks would fall to 250 minutes* and then 50 weeks later it would adjust again to ~60 minutes and then 12 weeks later it would adjust again to ~15 minutes ....

On edit: * network difficulty adjustment capped at 1/4 and 4x.  Of course rules can be changed and is Bitcoin is "stuck" there will be significant consenus to adjust the difficulty either as a one time change or a more adaptive difficulty algorithm.


There is no probable scenario where even a malicious removal of hashpower would result in block time taking a year or more.   1 year = 87,600 minutes.  10 minute target = 8,760x larger.  1/8,760 = 0.014%.  It would require 99.986% of the network to shutdown overnight.   Since no single entity owns 99.986% of the network, hell no contininent has that much we likely are talking an extinction level event (i.e. 99.986% of nodes go offline because they no longer exist due to an asteroid impact). :)

DeathAndTaxes, thats a perfect explanation.

Thank you.

Sorry, but no. The difficulty changes are capped at max 4x current difficulty and 1/4th current difficulty.

Edit:

https://github.com/bitcoin/bitcoin/blob/master/src/main.cpp

main.cpp, line 1299, GetNextWorkRequired(...)

specifically, lines 1338 ... 1341:

Very interesting.

Then someone with sufficient hashpower (lets say someone with an ASIC production line, and infinite paper money) could cause some problems to the network if suddenly remove their hardwares.

Obviously such an attack would not come from someone who seeks profit in mining, but would come from someone with an interest in weakening the bitcoin markets.

And, of course, a Extinction Level Event could cause some problems to bitcoin too ;D

Mining a block takes 10 minutes in average. But it may take 10 seconds or 10 weeks as well. Did anybody make a calculation, what's the probability that it will take a week to mine a single block under normal conditions (i. e. when difficulty is adequate to the total hashing power)?

i Rusia


my pc configuration


1 gigagers
1 ram memor gb
32 video

lol


you hapy if make

akes 10 minute


i cry  ::)

I meant it takes 10 minutes for the whole network of course, not for individual miner.

The lower the better :)

I've seen many guesses and opinions about but a real calculation done by someone who understands the subject has not yet been done, or at least published.

Bitcoin mining is a poisson distribution.  It is far easier to just use a poisson distribution calculator (online, graphing calculator, mathematica).

In 1 hour the expected # of events (blocks) is 6.  The probability that there will be 1 or less is ~1.7%
In 2 hours the expected # of events (blocks) is 12.  The probability that there will be 1 or less is ~0.01%

In 24 hours the expected # of events (blocks) is 144.  The probability that there will be 1 or less is essentially 0  (4.198 E-61)

So you're saying there's still a chance?
 ;D

Using the same numbers you can say:

1 hour block times should happen approximately once every 58 hours.
2 hour block times should happen approximately once every 80 days.
1 day block times should happen approximately once every 8*10⁴⁵ universe lifetimes (34 billion years).

im more worried about operation involving governmental agencies around the globe shutting down most major pools at once. we need to be more concerned aboud pool safety imho.

+1

it wouldn't be pleasant but it wouldn't be the end of the world ether. most miners would just operate without a pool, even with out expecting to profit monetarily just to spite the ass holes who attacked their pools. i know i surely would and if you took a pole I'm willing to bet it would corroborate my claim.

I think the greed is destroying the decentralization of Bitcoin with an excessive concentration in the pools.
But that still does not have have a simple solution.

Pools are no more concentrated than they were two years ago.  If anything they are marginally less concentrated and a significantly higher solo %.

We have a historical record of this information? an chart would be great to understand that.

My reasoning when I made the statement is grounded *also* on the following link.


https://en.bitcoin.it/wiki/P2Pool (https://en.bitcoin.it/wiki/P2Pool)

The moment that centralization became an issue people would switch to less populated pools and the network would become less centralized and the problem would self correct. Thats the beauty of the situation. the equipment that is operating these pools is spread all over the world and can firctionlessly move between pools so the appearance of centralization that we see from that pi chart up there is very misleading.

That is a good point to think about, but often people can not see beyond their options, they just choose whichever is easier and profitable for them.
A larger pool means gains more stable and therefore there is a tendency of centralization over the years.

if you leave the biggest pool alive and pull the plug on three smaller pools at the same time then you pretty much gonna have 51% attack...

Whew. Thank you very much, this answers my question :-)

It's a trivial calculation, and numbers have been published multiple times.

Use the right terms, Bitcoin mining is a Poisson process. The number of blocks in a period of time follows the Poisson distribution.

The numbers are good but I think it is more useful to think in terms of the time until the next block, which follows the exponential distribution. If the average is 10 minutes, the chance that the next block will be later than a day (1440 minutes) is exp (-1440/10) = 2.9 E-63.

As for the original question re a week, that's exp(-7*1440/10) = 1.7 E-438.

Who cares about pool safety when everyone isn't making money mining it :(

thats true but its important to understand the limitations of a temporary 51% attack. You cant just say "mowa ha ha ha" and write yourself 1 trillion bitcoins. Now a sustained 51% attack could be a more serious problem but there is no reason to expect the above outlined situation to lead to a sustained 51% attack.

Exactly, and this is a serious thing to think about.

Thanks for the additional information.
This is certainly a very interesting subject.

A point I made months ago…..

Also consider if two or three pool operators decided to work together……. with a high speed link between the 3….

Think about a very big country where cheap electronics comes from…….

This is also a way to inflate bitcoins..

1. Shutdown 50% miners; half of usual blocks found; (25 * 3 * 24 * 14) for two weeks; >> 25200 BTC
2. Difficulty down to half of usual
3. Bring those 50% miners back, (25 * 12 * 24 * 14)  for another two weeks; >> 100800 BTC
4. Usual for a month (25 * 6 * 24 * 28); >> 100800; excess, 25200 BTC

May be someone is already doing this. Right? :)

Difficulty adjustment is based on block count, not time. With half the miners gone, difficulty will take 4 weeks to adjust. And when they double the hashing power again, it will take 1 week. So essentially, the result will be that it takes 5 weeks to mine the blocks that usually takes 4 weeks.