[TekMol]

$705k per hour for Bitcoin - these numbers sound very expensive.

Do they take into account that during an attack the attacker will earn block rewards and transaction fees?

Because if not, then they vastly overestimate the costs.

This sounds like it is based on the some energy price that would be needed to do 51% of Bitcoins hashing.

Doing so could very well be profitable.

The reason it would be hard to do is that the attacker would have to gather a ton of hardware that way way exceeds the energy costs.

[ecwilson]

I was actually shocked that it could be this low and thought it must be wrong. Other sources have suggested it would cost over $1B:

https://u.today/guides/blockchain/bitcoin-51-attack-how-it-w...

> The hash rate is currently about six exahashes per seconds. Considering the most efficient ASIC miner with a hash rate of about 13,000 GHS (using the SHA-256 algorithm) being sold for about $2,100, an attacker will require about 500,000 hardware units and this will amount to about $1,005,000,000. When we factor in the cost of electricity and cooling daily, this figure rises to $1,006,000,000.

https://cryptoslate.com/analysis-bitcoin-costs-1-4-billion-t...

> To successfully conduct a 51 percent attack on the Bitcoin network would cost an incredible $1.4 billion. This massive network supports over 5 million specialized ASIC mining computers, consuming a total of 29 Terawatt hours of electricity a year—as much as the entire country of Morocco. One of the underpinnings of the Bitcoin network is...

https://gobitcoin.io/tools/cost-51-attack/

> $17,562,078,097, Hardware cost only, at cheapest rate. The attack would consume 241,478,573.839 kWh per day. (12,073,928.692$ per day)

[lftl]

The calculations you cite and what the linked page are fundamentally different. The numbers you're citing are roughly what it would cost to buy hardware that would continuously be capable of mounting a 51% attack. The linked site is estimating how much it would cost to rent existing capacity to mount an hour-long 51% attack.

[SkyMarshal]

I think the site assumes you already have the hardware, and is just calculating the OpEx of the attack, not the CapEx. Like, if a major mining pool decided to 51% attack a coin.

[glofish]

I agree, it feels way too cheap to be true.

[rzwitserloot]

If you follow the 'about' link, it explains that any mining rewards are _not_ included, and that including them would reduce the cost 'somewhere around 80%' (not sure where that number is derived from but it sounds plausible).

[exdsq]

There's no way I believe $705k would work. The company they're pricing that off of don't have the computational ability to run a 51% attack. I'd be interested to know how the entire power of the bitcoin network compares to say AWS or Azure?

[RL_Quine]

AWS and Azure would be using CPUs, GPUs, and FPGAs, which have nowhere near the sort of speeds as dedicated hardware. It's something in the order of a trillion desktop CPUs to equal the same hashrate as the bitcoin network is currently.

[glofish]

For me, the numbers feel surprisingly "affordable". Is this list even correct?

I am not talking about my own pocket, but rich people or powerful entities. This is the cost of a military drone or something.

Imagine a nation adopting Bitcoin then another nation taking over that infrastructure.

We are talking about controlling the entire Bitcoin universe, everyone has to accept what the attacker considers "correct"

[caymanjim]

$705k/hr is so low as to be unbelievable. You need to at least temporarily out-compute everyone else in the world, and there's a lot of horsepower behind Bitcoin.

[Kiro]

I thought it would be magnitudes more expensive, to the point where it would be unrealistic to even try. I thought that was the whole point with PoW.

[pat2man]

Only of those blocks are accepted by the chain in the future. Zero transaction blocks or blocks with invalid transactions could easily be ignore by the next miner.

[TekMol]

Well, the reason for an attack is to reverse transactions. For that to have any value, the blocks must be accepted by the chain in the future.

And no, a miner can not "easily" ignore previous blocks.

And blocks with invalid transactions get ignored by everyone anyhow.

[flir]

Nah, the reason is to split the head of the chain for a period of time, and do different things in each chain. Then when one of the heads is declared "true", you gain advantage (typically you spend the same coins twice, once in each head).

[greenshackle2]

You say "nah", but what you are describing is reversing a transaction, I don't see how that is disagreement.

From the POV of the recipient, when the split branch becomes the "non-true" branch, it looks like they got the money but then it disappeared.

[pat2man]

If you are considering the recipient a human interpreting the results, then this is a failure of their wallet UI. The block chain is a tree not a log. The views that show it as a log are just showing you the statistically most likely outcome. If you look at the raw data you see all possibilities.