Cost of a 51% attack for different cryptocurrencies?

Okay I see what you mean about replacing the work assignments going to the miners -- if you could tell them to solve a different block/fingerprint (hash of new block + previous block) and receive their output, then you can steal their hashing power. But I'm still not sure what you mean here:

>>If you mean the traffic of mining pools communicating their solutions to the pool's "mother brain", those are already cryptographically attached to a solution that pays out to specified addresses.

>That's not correct in practice. There's no authentication of the work going to the miner at all, so an attacker can just change the destination before the miner even sees the work.

I was referring here to the solutions the miners send out. That does not need to be authenticated because it's already attached to the block they were solving for -- i.e. it is a proof of work valid only for a specific block. If they received the correct block and nonce range to check, then the solutions are useless to anyone else. Diverting their traffic would just reduce the mining pool's hash power, not give it to anyone else.

So yes, I see how you could steal the miner's hash power if you could replace the assignment the pool head was giving them, and then see the output, but I don't think it's correct to say that solutions are vulnerable to being stolen after getting the correct assignment "because they don't authenticate" -- the proof of work is only valid for that block, and so could only be destroyed, not stolen.

You're fundamentally missing the point somehow.

When you connect to a pool, you give them absolute trust over what you're mining using your hardware with the expectation that they will pay you for it later. In a route hijack, an attacker can replace the pool and announce their own work to you, and receive all results you produce. You can not distinguish this with the normal behavior of the pool and will be robbed, and your work can be used to do whatever the attacker wishes.

The output of the work being loosely "authenticated" with the pool by virtue of the work being non-transferable is entirely orthogonal. Nobody is going to be taking that because it's worthless, as you correctly point out. They're going to replace the work that's sent to you in the first place, because that's what makes sense.

I pointed this out elsewhere in this comment thread, but resurfacing here since it's perhaps not as clear as it should be: The attack cost is based on the the extrapolated cost of attacking the given coin based on the current hashing price on nicehash. If Another caveat: It's potentially cheaper to attack these coins than the number shown on this site since you receive block rewards from the time period when you attack a coin. In a lot of cases this will recover a majority of the money you spend on the attack. That said, this isn't guaranteed, and you are forced to put up this amount of money in order to carry out the attack.

Disclaimer: I built crypto51 ~a year ago

Pretty sure I'm not missing the point, because that's exactly what I said, in different words.

I specifically agreed that, if you can replace the assignment given to the miners ("replace the pool and announce their own work to you"), and see the output, then you can steal the work. It was in this paragraph:

>>Okay I see what you mean about replacing the work assignments going to the miners -- if you could tell them to solve a different block/fingerprint (hash of new block + previous block) and receive their output, then you can steal their hashing power.

That is an agreement with your:

>In a route hijack, an attacker can replace the pool and announce their own work to you, and receive all results you produce.

That is me communicating agreement that that's the attack that "makes sense" as in your sentence here:

>They're going to replace the work that's sent to you in the first place, because that's what makes sense.

I made my original because it sounded like you were saying a miner not (separately) authenticating their output to the pool would be an issue, which I now see you (always) agreed is orthogronal; my only objection in the follow-up was that your comment was addressing something different than I originally raised:

>>>That's not correct in practice. There's no authentication of the work going to the miner at all, so an attacker can just change the destination before the miner even sees the work.

>>I was referring here to the solutions the miners send out.

So, if I agree with you on every question of what and where the threat is and is not, and said so with slightly different words than you did, what point do you think I'm fundamentally missing?

Nicehash has .99% of what you need to have 51% of the hashrate, not .5%. But that's still too tiny.

However.

You don't need 51% of the hashes to have the longest chain. The longest chain is a lottery. If you had 25% of the TH/s out there, there are 3x as many hashes you don't control as do. The odds are 1:3 that you will still find the next hash. If that weren't the case, there'd be no point at all in me having .0001% of the TH/s. I'd be better off setting the money on fire to heat my house.

Bitcoin doesn't have a consensus algorithm on two counts. The obvious one is that everyone takes the longest chain, regardless of whether everyone already agreed to a shorter chain. In Raft, your history can roll back if there's a partition. In Bitcoin, things can be rolled back even if everyone is online. I need one attack (rewrite history), not two (rewrite history + DOS attack), and because of that, nobody but my pocketbook notices if I try and fail.

The second one is that there is no consensus on what transactions to include in the next hash. Any hasher could blacklist transactions that are unfavorable to them without really affecting their odds of finding the next hash. I think it's assumed that it's not in the interest of either mining hardware owners or frequent cryptocurrency spenders to do this, as they would destabilize their own investment. That only borrowed hardware would be used that way, and on short bursts of purchases. But is that really true? Or is there a zero-day attack out there already being used or waiting to be found?

I'm thinking of the epic embezzling scandals that have turned up. How many people out there were never caught, or were insufficiently prosecuted? Employees are usually subject to the laws where the office is located. These people could be on the other side of the world.