The situation was designed by consumer:croraf and me in discussing a query of mine yesterday. To make it extra clear, I wish to current it right here once more in a stricter design.
To do it in a transparent method, first 4 assumptions:
- Transactions are accepted when N blocks affirm them.
- We are able to make contact to the vast majority of the miners, they’re egoistic and barely invested within the PoW foreign money.
- An assault with the vast majority of mining energy is feasible. To make it extra clear: We assume that rewriting blockchain historical past with undoing many transactions is so shocking, that we will get our advantages from the assault earlier than the foreign money goes down.
- There may be an alt coin, resistant in opposition to our following assault situation, with out worth correlation to PoW currencies. Mining {hardware} permits to mine the alt coin in addition to the PoW foreign money.
Now the assault situation.
We do a transaction with a better worth than mining advantages from N blocks. We wait till N blocks affirm our transaction, so the transaction is accepted by assumption 1. Than we bribe the vast majority of miners to create a fork to make our transaction undone. The bribe have to be solely a bit bit greater than the mining advantages on the “actual” chain as a result of they’re egoistic and should not all in favour of hold the foreign money alive by assumption 2. Solely paying the bribe the price of the assault could be very low relative to the promised win! The miners and we get our advantages from the assault earlier than the foreign money is down by assumption 3. Then the PoW foreign money perhaps goes down, however the bribed miners can go to mine the alt coin with none loss, what is feasible by assumation 4.
The place is the fault, within the assault situation or within the assumptions?
I believe the assault situation is right and the prompt faults within the assumptions from the dialogue yesterday cannot persuade my.
A very powerful critics I already know:
Assumption 1: We must always solely belief transactions with values comparable with mining prices, however this makes the foreign money inefficient, which was confirmed right here.
Assumption 3: When you do not belief this assumption, so that you deny regular assault situation of PoW foreign money. When you accomplish that, why should not we do PoW with a really low problem and a really small mining energy then?
EDIT: I believe we will skip assumption 3 by doing the assault with a brief place which implies we do the excessive worth transaction to start with with cryptos we have now lended. I appears clear that the foreign money goes down after such a giant assault and so we even revenue from the quick.