It doesn't 'have' to be high. The hash rate could be 1/1000 of what it is today without any risk to 'settlement assurance'
You could pay $384k to hire miners to 51% attack BTC right now (that is, if NiceHash had the capacity). If you cut the hash rate that much the cost would be only $400 or so.
Does it sound like a secure trustless currency if anyone can pay $400 to gain 51% majority?
EDIT: 51% attack != rewrite blockchain
Furthermore, any blocks that were mined under high hashpower still need the same hashpower to be re-mined. A one-time reduction in network hash power doesn’t make previously mined blocks easier to mine.
0.009 BTC/PH/day to buy from NiceHash (https://www.nicehash.com/algorithm/sha256)
100,000 PH/day total hashrate of BTC network (https://www.blockchain.com/charts/hash-rate)
That's 450 BTC/day to buy 50% of the hash rate (as if you even could, that in itself is a ridiculous notion - NiceHash says they have only 300 PH).
Or 18.75 BTC/hour. Or $185,000/hour.
Of course, you're not going to buy 50% of the network's currently running hash power. You'd likely need closer to 100% of the network's current hash power to gain 51%.
Also people may misinterpret 'rewriting history' as the ability to to change coins sent from A -> B to A -> C. Which it is not.
Not saying an attack still isn't bad, but let's be clear what the extent of the damage could and could not be.
2: If you are A (and regardless of whether you're also C) and you sent money to B during the 400$/hr (less than a high-profile lawyer, and probably faster to boot) attack, then yes, changing coins sent from A -> B to A -> C is exactly what you can do.
No, it's $400,000 per hour.
0.009 BTC/PH/day to buy from NiceHash (https://www.nicehash.com/algorithm/sha256)
100,000 PH/day total hashrate of BTC network (https://www.blockchain.com/charts/hash-rate)
That's 450 BTC/day to buy 50% of the hash rate (as if you even could, that in itself is a ridiculous notion - NiceHash says they have only 300 PH).
Or 18.75 BTC/hour. Or $185,000/hour.
Of course, you're not going to buy 50% of the network's currently running hash power. You'd likely need closer to 100% of the network's current hash power to gain 51%. So, $400,000/hr.
I mean really, does it pass any sort of common sense test that you could 51% the bitcoin network for $400 per hour?
> If you cut the hash rate that much the cost would be only $400 or so.
> during an attack which costs 400k per hour
> under your proposal [of reducing the hash rate by a factor of 1000]
Perhaps I should have been more explicit, but it certainly isn't necessary.
> So, $400,000/hr.
Which, if the hash rate was "1/1000 of what it is today", would be reduced to 400$/hr.
If we cut the hash rate tenfold, which is definitely significant, you'd still need to find someone who has hundreds of thousands of dollars of motivation to perform an attack. Having that motivation is hard when it takes a huge amount of double spending all at once, the attack will damage the integrity of the coin, and clients can be modified to be highly resistant to it.