5 ms·

If my goal is to re-purpose, I would use a General Purpose Computer The Market Cap of Bitcoin is $184,000,000,000 I have plenty of money to play with.

nybble41 7y ago
If your plan is to use general-purpose computers for mining then Bitcoin has nothing to worry about. You'll never manage a 51% attack that way, no when all your competition is using ASICs. Moreover, to gain $184B by shorting Bitcoin you'd need to find someone willing to loan you $184B worth of Bitcoin, and then somehow sell all of it without crashing the price or drawing unwanted attention to your activities. Of course if the price doesn't react the way you expect you could end up paying a lot more than $184B to buy it all back to repay the loan. You shouldn't assume that even a successful (but expensive, and obviously temporary) 51% attack will drive the price down to zero.
- qroshan 7y ago
  It all depends on who is doing the attacking. If the attacker is a state government or someone with billions of dollars and compute to spare, ASICs aren't going to fight this losing battle. Heck, you can buy off the ASIC miners for a few million dollars (all we have to cover is their net profit, which is pretty low)
  - kragen 7y ago
    The cost of mounting the attack with general-purpose computers would be orders of magnitude higher than the US$12B calculated above, just from the energy bill. Check out https://en.bitcoin.it/wiki/Mining_hardware_comparison; https://en.bitcoin.it/wiki/Mining_hardware_comparison; the ASIC AntMiner S9 gets 10 billion hashes per joule, while on https://en.bitcoin.it/wiki/Non-specialized_hardware_comparison https://en.bitcoin.it/wiki/Non-specialized_hardware_comparis... you can see that the most efficient GPUs get 2–3 million hashes per joule, 3000 to 5000 times less. So instead of spending US$12 billion on hardware and US$4 billion per year on power, you'd be spending US$12 trillion per year on power. No state has such a large budget; that's more than half of the US GDP, and about 15% of world GDP. That's more than the amount of marketed energy produced in the world. That is, the attack you're proposing would require commandeering 15% of the world economy and more than doubling world electrical generation capacity. Bribing or backdooring ASIC miners is a far more likely vulnerability.
    - lonelappde 7y ago
      Are ASICs totally useless for non Bitcoin computing?
      - kragen 7y ago
        Yes, that's what the “AS” stands for.
        mikekchar 7y ago
        To be a bit more specific, the ASIC is a computation built in hardware. It can do that computation and that computation alone. The algorithm in Bitcoin does absolutely nothing useful -- you are just hashing a random number and seeing if the result is below a certain value. Since you can't change the computation on the ASIC, it's absolutely useless for anything except mining bitcoins.
        perl4ever 7y ago
        Maybe this is dumb/naive, but I've wondered for quite a while - what if you take the latest deep learning/AI techniques and try to train a system to predict the approximate size of the hash from the input number? Has anyone seriously tried and failed?
        mikekchar 7y ago
        If you could do it, you'd be famous for more than BTC. It would mean that you could factor numbers in polynomial time. Long story short, calculating the hash for BTC is intended to be a non-polynomial problem. If you can find a method (any method) that will reduce the search space of the answer such that you can calculate it in polynomial time, then you have proved that NP=P (If you can find a way to solve any non-polynomial-time-hard problem in polynomial time, then it means that all NP hard problems can be solved in P time). This would completely break all current encryption. Most people think that this is impossible, but it has not been proven yet. Unless you had some reason for believing the technique would work, it's probably not worth the effort to try.
  - solveit 7y ago
    It doesn't matter if the US government is doing the attacking, they're not winning with general purpose hardware. ASICs are literally thousands of times faster with lower power consumption than GPUs. Also, any state attacker worth their shit would have the ability to develop their own ASICs so I don't know why you're hung up on using general purpose hardware. Finally, you certainly cannot buy off the ASIC miners with a few million, not least because they own billions of dollars worth of ASICS that can't do anything but mine Bitcoin, and a successful state-orchestrated attack on Bitcoin would make all of them worthless. I don't think a state government taking down Bitcoin by its own rules is completely impossible, but you don't seem to have any grasp of the scales involved.
  - nybble41 7y ago
    State governments have simpler and more reliable ways to attack the system. Like armies. Buying off the miners would require at least a few hundred million dollars—you'd need to buy the hardware to pull off an attack like that, not just rent it for a while. And you still wouldn't manage to get anywhere near the full market cap by shorting Bitcoin while you do it. You'd never find anyone crazy enough to loan you that much. A small fraction, perhaps. Not enough to cover your expenses. And in the end, after your massive investment, the community would just make some trivial change to the protocol and completely ignore the attack. Really, if this sort of thing was so easy then everyone would be doing it. You're certainly welcome to try.
    - lonelappde 7y ago
      You're ignoring diplomacy. An army is a very unsubtle attack that might have unwanted geopolitical consequences.
  - celticninja 7y ago
    First of all hardware is a bottleneck, so likely the state needs to procure or manufacture their own. Which delays the start of the attack, during which time the network will continue to grow. The state cannot just magic ASIC devices from nowhere.

nybble41 7y ago

If your plan is to use general-purpose computers for mining then Bitcoin has nothing to worry about. You'll never manage a 51% attack that way, no when all your competition is using ASICs. Moreover, to gain $184B by shorting Bitcoin you'd need to find someone willing to loan you $184B worth of Bitcoin, and then somehow sell all of it without crashing the price or drawing unwanted attention to your activities. Of course if the price doesn't react the way you expect you could end up paying a lot more than $184B to buy it all back to repay the loan. You shouldn't assume that even a successful (but expensive, and obviously temporary) 51% attack will drive the price down to zero.

qroshan 7y ago
It all depends on who is doing the attacking. If the attacker is a state government or someone with billions of dollars and compute to spare, ASICs aren't going to fight this losing battle. Heck, you can buy off the ASIC miners for a few million dollars (all we have to cover is their net profit, which is pretty low)
- kragen 7y ago
  The cost of mounting the attack with general-purpose computers would be orders of magnitude higher than the US$12B calculated above, just from the energy bill. Check out https://en.bitcoin.it/wiki/Mining_hardware_comparison; https://en.bitcoin.it/wiki/Mining_hardware_comparison; the ASIC AntMiner S9 gets 10 billion hashes per joule, while on https://en.bitcoin.it/wiki/Non-specialized_hardware_comparison https://en.bitcoin.it/wiki/Non-specialized_hardware_comparis... you can see that the most efficient GPUs get 2–3 million hashes per joule, 3000 to 5000 times less. So instead of spending US$12 billion on hardware and US$4 billion per year on power, you'd be spending US$12 trillion per year on power. No state has such a large budget; that's more than half of the US GDP, and about 15% of world GDP. That's more than the amount of marketed energy produced in the world. That is, the attack you're proposing would require commandeering 15% of the world economy and more than doubling world electrical generation capacity. Bribing or backdooring ASIC miners is a far more likely vulnerability.
  - lonelappde 7y ago
    Are ASICs totally useless for non Bitcoin computing?
    - kragen 7y ago
      Yes, that's what the “AS” stands for.
      - mikekchar 7y ago
        To be a bit more specific, the ASIC is a computation built in hardware. It can do that computation and that computation alone. The algorithm in Bitcoin does absolutely nothing useful -- you are just hashing a random number and seeing if the result is below a certain value. Since you can't change the computation on the ASIC, it's absolutely useless for anything except mining bitcoins.
        perl4ever 7y ago
        Maybe this is dumb/naive, but I've wondered for quite a while - what if you take the latest deep learning/AI techniques and try to train a system to predict the approximate size of the hash from the input number? Has anyone seriously tried and failed?
        mikekchar 7y ago
        If you could do it, you'd be famous for more than BTC. It would mean that you could factor numbers in polynomial time. Long story short, calculating the hash for BTC is intended to be a non-polynomial problem. If you can find a method (any method) that will reduce the search space of the answer such that you can calculate it in polynomial time, then you have proved that NP=P (If you can find a way to solve any non-polynomial-time-hard problem in polynomial time, then it means that all NP hard problems can be solved in P time). This would completely break all current encryption. Most people think that this is impossible, but it has not been proven yet. Unless you had some reason for believing the technique would work, it's probably not worth the effort to try.
- solveit 7y ago
  It doesn't matter if the US government is doing the attacking, they're not winning with general purpose hardware. ASICs are literally thousands of times faster with lower power consumption than GPUs. Also, any state attacker worth their shit would have the ability to develop their own ASICs so I don't know why you're hung up on using general purpose hardware. Finally, you certainly cannot buy off the ASIC miners with a few million, not least because they own billions of dollars worth of ASICS that can't do anything but mine Bitcoin, and a successful state-orchestrated attack on Bitcoin would make all of them worthless. I don't think a state government taking down Bitcoin by its own rules is completely impossible, but you don't seem to have any grasp of the scales involved.
- nybble41 7y ago
  State governments have simpler and more reliable ways to attack the system. Like armies. Buying off the miners would require at least a few hundred million dollars—you'd need to buy the hardware to pull off an attack like that, not just rent it for a while. And you still wouldn't manage to get anywhere near the full market cap by shorting Bitcoin while you do it. You'd never find anyone crazy enough to loan you that much. A small fraction, perhaps. Not enough to cover your expenses. And in the end, after your massive investment, the community would just make some trivial change to the protocol and completely ignore the attack. Really, if this sort of thing was so easy then everyone would be doing it. You're certainly welcome to try.
  - lonelappde 7y ago
    You're ignoring diplomacy. An army is a very unsubtle attack that might have unwanted geopolitical consequences.
- celticninja 7y ago
  First of all hardware is a bottleneck, so likely the state needs to procure or manufacture their own. Which delays the start of the attack, during which time the network will continue to grow. The state cannot just magic ASIC devices from nowhere.