6 ms·

The 51% attack works because you can use the majority of CPU hash power to write a longer chain faster than the rest of the network. I don't quite follow what

The 51% attack works because you can use the majority of CPU hash power to write a longer chain faster than the rest of the network. I don't quite follow what you mean here: longest chain wins is a central tenet of cryptocurrency design, and even if you did something with consensus in the product a majority could still hardfork away from that design. Am I missing something here?

hujun 10y ago
the value of 51% is something I failed to understand , wouldn't the attack also works even the attacker has less than 50%, but bigger than any other individual miner? for example if there are 3 miners in total, A has 40%, B and C has 30% each, wouldn't A still able to write a longer chain faster than B or C?
- wmf 10y ago
  A is working on one chain but B and C are working together on another chain, so the A chain has 40% and the B/C chain has 60%.
- hujun 10y ago
  "A is working on one chain but B and C are working together on another chain, so the A chain has 40% and the B/C chain has 60%." but if B and C are working together, it implies there is some sort of relationship between them so they could be coordinated together(e.g. owned by same org), this not the case I am trying to use here; my case is really 3 independent miners
  - wmf 10y ago
    The default behavior of Bitcoin is for all miners to cooperate even if they are independent.
- SirensOfTitan 10y ago
  It would be in B and C's best interests to hash together to avoid A's attack. A well designed cryptocurrency takes these game theory scenarios into accounts and properly incentivizes mining wherein it should be more profitable for miners to accurately represent transaction history over destabilization. A in your scenario would likely be malicious to the network would have to be a state actor looking to kill the network. Luckily, in a sufficiently large network even governments are bound by CPU/GPU supply. It gets even harder for this kind of state maliciousness to take place in tech like ethereum: whose PoW function is both CPU and memory bound (I.e. You cannot use custom ASICs) I casually enjoy cryptocurrency, so anyone who knows better please correct me if you find me incorrect.
derefr 10y ago
I guess you could just require that, in the case of competing chains that have n linearized entries in common, the winner has to build a chain n+2m long as the next-best contender of n+m length, rather than just a constant n+6 as long as in current chains. So if there were two active pluralities with 33% of the hashing power each, both trying to rewrite history, you'd just have two active chains forever and never end up linearizing (which might be a good state to end up in; sort of a "SybilAttackException raised; hard-fork with added policy rule choosing a winner to continue.")

hujun 10y ago

the value of 51% is something I failed to understand , wouldn't the attack also works even the attacker has less than 50%, but bigger than any other individual miner? for example if there are 3 miners in total, A has 40%, B and C has 30% each, wouldn't A still able to write a longer chain faster than B or C?

wmf 10y ago
A is working on one chain but B and C are working together on another chain, so the A chain has 40% and the B/C chain has 60%.
hujun 10y ago
"A is working on one chain but B and C are working together on another chain, so the A chain has 40% and the B/C chain has 60%." but if B and C are working together, it implies there is some sort of relationship between them so they could be coordinated together(e.g. owned by same org), this not the case I am trying to use here; my case is really 3 independent miners
- wmf 10y ago
  The default behavior of Bitcoin is for all miners to cooperate even if they are independent.
SirensOfTitan 10y ago
It would be in B and C's best interests to hash together to avoid A's attack. A well designed cryptocurrency takes these game theory scenarios into accounts and properly incentivizes mining wherein it should be more profitable for miners to accurately represent transaction history over destabilization. A in your scenario would likely be malicious to the network would have to be a state actor looking to kill the network. Luckily, in a sufficiently large network even governments are bound by CPU/GPU supply. It gets even harder for this kind of state maliciousness to take place in tech like ethereum: whose PoW function is both CPU and memory bound (I.e. You cannot use custom ASICs) I casually enjoy cryptocurrency, so anyone who knows better please correct me if you find me incorrect.

derefr 10y ago

I guess you could just require that, in the case of competing chains that have n linearized entries in common, the winner has to build a chain n+2m long as the next-best contender of n+m length, rather than just a constant n+6 as long as in current chains. So if there were two active pluralities with 33% of the hashing power each, both trying to rewrite history, you'd just have two active chains forever and never end up linearizing (which might be a good state to end up in; sort of a "SybilAttackException raised; hard-fork with added policy rule choosing a winner to continue.")