6 confirmations questions

[hosseinimr93]

But... When i try to reverse the last (let's say) month: I'd have to go back to (x-4464) => 6 blocks/hour * 24 hours/day * 31 days/month.
By the time i reached height (x), the rest of the network would have reached height ~(x+4374). Oops

I don't understand how the 4374 was obtained.

Let's say I have 51% of the hashrate and 49% of the hashrate is owned by honest miners.
I mine 4464 blocks during a month. Number of blocks mined by honest miners can be easily calculated using proportion method.

So, number of those blocks would be 4464*(⁴⁹/₅₁) = 4288.

Am I missing something?

[mocacinno]

But... When i try to reverse the last (let's say) month: I'd have to go back to (x-4464) => 6 blocks/hour * 24 hours/day * 31 days/month.
By the time i reached height (x), the rest of the network would have reached height ~(x+4374). Oops

I don't understand how the 4374 was obtained.

Let's say I have 51% of the hashrate and 49% of the hashrate is owned by honest miners.
I mine 4464 blocks during a month. Number of blocks mined by honest miners can be easily calculated using proportion method.

So, number of those blocks would be 4464*(⁴⁹/₅₁) = 4288.

Am I missing something?

nah, you're probably right...I had a hectic day so far, filled with discussions about a huge database scheme and i'm left with most of my ability to concentrate gone. To this point, i'm still unable to get my head wrapped around the method used to solve this problem...  This evening, when i'm back to normal, i'll probably either completely agree with what you said, or i'll disagree (altough those odds are small).

My train of thought was pretty simple: there's a 2% difference in hashrate, so if the attacker generates 100 blocks, the honest miner creates 98. If the attacker creates 4464, the honest miner creates 4464 - (4464*0.02).

The conclusion still remains the same tough: if you want to roll back a longer time of historic blocks, the time you'll need is a lot more than just the time you need to mine said blocks, since the honest miners will keep adding new blocks on top. If you decide to do a roll back of future blocks to the state at this point in time, this isn't the case.

[hosseinimr93]

My train of thought was pretty simple: there's a 2% difference in hashrate, so if the attacker generates 100 blocks, the honest miner creates 98. If the attacker creates 4464, the honest miner creates 4464 - (4464*0.02).

Yes, The difference is 2%. But actually honest miners hashrate is 3.92% smaller than hashrate of the attacker. If the attacker mines 100 blocks, honest miners mine 96.08 blocks.

So, number of blocks mined by honest miners should be 4464 - (4464*0.0392) = 4288

The conclusion still remains the same tough: if you want to roll back a longer time of historic blocks, the time you'll need is a lot more than just the time you need to mine said blocks, since the honest miners will keep adding new blocks on top. If you decide to do a roll back of future blocks to the state at this point in time, this isn't the case.

You are 100% right. that doesn't make any difference to the conclusion.

[philipma1957]

Asssume that such 1-month attack happens, its cost will be about $4,250,952 ($590,410*24 hours*30 days).

You've missed a few digits there. Using those numbers, the cost of a 1 month attack would be $425 million. Although you should also factor in that an attacker who manages to overturn a month of blocks would gain 27,000 BTC in block rewards (plus potentially fees if they chose to include other users transactions in their blocks), which at current prices would give them $280 million, so lowering the cost of a month long attack to around $145 million.

I would argue you can not calculate it that way. Simply because access to the amount of gear/hashrate is not possible for anyone to do.

The only way to attack the network at a 51% rate would be to divert the 3 largest pools via hijacking of the hashrate. If this was possible miners would shift to other pools. The attacker would need to be able at access pools at will to divert the hash to his address.

Lessor networks can be attacked.

BCH
BSV could be hit for a 51% attack not that hard

viabtc.com could do it on the sneak. viabtc has 9eh mining at btc they could simply pay the miners out of pocket and divert the the hash to attack with bsv or bch.

[o_e_l_e_o]

The numbers might be ballpark correct, but without seeing the actual calculations, they're just numbers...

Totally agree, but they do give an indication of just how costly it is to overturn even a handful of confirmations. For the average user who might be spending/sending/trading up to a few bitcoin, 6 confirmations if more than enough to consider any trades "final", as the cost of reversing those confirmations far outweighs the value of the transactions.

My train of thought was pretty simple: there's a 2% difference in hashrate, so if the attacker generates 100 blocks, the honest miner creates 98. If the attacker creates 4464, the honest miner creates 4464 - (4464*0.02).

Nah, hosseinimr93 is right. Although there is a 2% difference when considering the sum of the hashrates, 51 is 4% greater than 49. Think of a 60%/40% split - 20% difference, but 60 is 50% greater than 40.

I would argue you can not calculate it that way. Simply because access to the amount of gear/hashrate is not possible for anyone to do.

I mean, if we are talking about someone controlling 51% of the hashrate for an entire month, then you can't really calculate it any way because such a thing is practically not going to happen. My comments are purely theoretical. Also worth pointing out that both BCH and BSV have already suffered 51% attacks in the past.

[Kakmakr]

I always imagine a scenario where I see a bunch of people standing around and 1 person kills a person .... now only 1 other person saw who did it and he is starting to tell the people around him what happened. So imagine the first person is block 1.. and the other who did not see it... are also being told over a longer period... until you get a bunch of people that know what happened.

Now imagine if I was the killer and I wanted to bribe people to stay quite... well, if I only had to bribe the first guy.. it would cost me very little, but if I have to bribe more and more... it would become very expensive... 

The same principle is applied to confirmations.... the more confirmations you get, the more it costs you to remove the evidence of your actions. (In the Blockchain that would apply to a transaction you done)