Topic: And if half of the miners turn off their hardwares ? - page 2. (Read 3009 times)

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)

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.

The lower the better

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

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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)?

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

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.

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:

DeathAndTaxes, thats a perfect explanation.

Thank you.

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).

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?

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

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.

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.

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.

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

Why? Higher the better.

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