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https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_computing_power https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_... Basically, someone

https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_computing_power https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_... Basically, someone who has the computing resources needed to do the same work as the rest of the network combined could create malicious forks of the block chain. They could then "reverse" transactions they had made, prevent other transactions from being confirmed, and interfere with "mining." This is polynomial time in the parameters of the system: it is just the sum of the work done by the honest parties. The constant factor is small, and the attack is not at all impractical; even if we generously assume that it would take $100 million of ASICs to carry out the attack, the US government spent 10 times as much on one NSA datacenter in Utah.

Xcelerate 14y ago
Ah, okay. I thought you were implying there was a polynomial attack on ECSDA, SHA-256, or RIPE-MD.
- betterunix 14y ago
  It is important to remember that Bitcoin is not a hash function or a signature system. Unfortunately, there seems to be no rigorous definition of "security" for Bitcoin, so it is somewhat difficult to understand what it means to "attack" Bitcoin. I suspect that any rigorous definition of Bitcoin's security would require a definition of money that lacks both authority and intrinsic value.
moe 14y ago
even if we generously assume that it would take $100 million of ASICs You always conveniently ignore the fact that legitimate mining is at the verge of shifting to ASICs, too. Perhaps your $100mio figure is accurate today, but it won't be long before you have to apply quite a significant multiplier to that.
- betterunix 14y ago
  In fact, $100 million is much larger than the situation today. I have seen estimates as low as $1 million and as high as $30 million.
  - moe 14y ago
    And you seriously assume an attacker with that kind of resources (be it millions or billions) would be dumb enough not to realize that a crash of bitcoin would merely spawn the next, more resilient crypto currency? That would have to be quite a large irrational player because this isn't compatible with today's corporate and government firmware (game theory) at all.
    - betterunix 14y ago
      Is there some reason to think a more "resilient" protocol is even possible? Can you even give a rigorous definition of the security properties these protocols are trying to achieve? That aside, do you really think the government would not try to destroy Bitcoin even if it meant a new system replaced it? Have you not been paying attention to what happened with Megaupload? Governments are perfectly willing to attack systems even when they know the systems will be replaced, just to disrupt the users of the system and pressure people to avoid them.
      - moe 14y ago
        Is there some reason to think a more "resilient" protocol is even possible? I'm not a bitcoin researcher but the first thing I'd have to note is that so far it's holding up not bad at all. At non-trivial scale and under permanent attack. Not a small feat for the first impl of a global, cross-platform P2P crypto money system, don't you think? Just consider the history of infinitely simpler systems (e.g. twitter). Furthermore there are various efforts underway (e.g. SolidCoin) to address the known weaknesses, even before we know whether any of them turns out to be a bigger problem than the issues that we take for granted in our current banking system (e.g. "too big to fail" or the perpetual banking crisis that has been going on for the past 10 years). That aside, do you really think the government would not try to destroy Bitcoin even if it meant a new system replaced it? Personally yes, I doubt any half-sane government will equate bitcoin with software piracy. Bitcoin addresses one of the core mechanics of society (money exchange). That's not even in the same ballpark as people downloading vampire movies without paying for them. just to disrupt the users of the system and pressure people to avoid them. This is where I think the average government would be smarter than you. You can't kill demand for something so useful unless you utterly convince a majority that it can not possibly work - here your piracy-analogy holds water again. They may indeed pull a Napster (we've seen how that played out) but I think it's much more likely they would try a very long-term, elaborate stealth attack to erode trust in p2p money systems as a whole. But just as with piracy this seems like a losing proposition. Unless a truly insurmountable flaw is discovered that renders any system with the features of bitcoin infeasible.

Xcelerate 14y ago

Ah, okay. I thought you were implying there was a polynomial attack on ECSDA, SHA-256, or RIPE-MD.

betterunix 14y ago
It is important to remember that Bitcoin is not a hash function or a signature system. Unfortunately, there seems to be no rigorous definition of "security" for Bitcoin, so it is somewhat difficult to understand what it means to "attack" Bitcoin. I suspect that any rigorous definition of Bitcoin's security would require a definition of money that lacks both authority and intrinsic value.

moe 14y ago

even if we generously assume that it would take $100 million of ASICs You always conveniently ignore the fact that legitimate mining is at the verge of shifting to ASICs, too. Perhaps your $100mio figure is accurate today, but it won't be long before you have to apply quite a significant multiplier to that.

betterunix 14y ago
In fact, $100 million is much larger than the situation today. I have seen estimates as low as $1 million and as high as $30 million.
- moe 14y ago
  And you seriously assume an attacker with that kind of resources (be it millions or billions) would be dumb enough not to realize that a crash of bitcoin would merely spawn the next, more resilient crypto currency? That would have to be quite a large irrational player because this isn't compatible with today's corporate and government firmware (game theory) at all.
  - betterunix 14y ago
    Is there some reason to think a more "resilient" protocol is even possible? Can you even give a rigorous definition of the security properties these protocols are trying to achieve? That aside, do you really think the government would not try to destroy Bitcoin even if it meant a new system replaced it? Have you not been paying attention to what happened with Megaupload? Governments are perfectly willing to attack systems even when they know the systems will be replaced, just to disrupt the users of the system and pressure people to avoid them.
    - moe 14y ago
      Is there some reason to think a more "resilient" protocol is even possible? I'm not a bitcoin researcher but the first thing I'd have to note is that so far it's holding up not bad at all. At non-trivial scale and under permanent attack. Not a small feat for the first impl of a global, cross-platform P2P crypto money system, don't you think? Just consider the history of infinitely simpler systems (e.g. twitter). Furthermore there are various efforts underway (e.g. SolidCoin) to address the known weaknesses, even before we know whether any of them turns out to be a bigger problem than the issues that we take for granted in our current banking system (e.g. "too big to fail" or the perpetual banking crisis that has been going on for the past 10 years). That aside, do you really think the government would not try to destroy Bitcoin even if it meant a new system replaced it? Personally yes, I doubt any half-sane government will equate bitcoin with software piracy. Bitcoin addresses one of the core mechanics of society (money exchange). That's not even in the same ballpark as people downloading vampire movies without paying for them. just to disrupt the users of the system and pressure people to avoid them. This is where I think the average government would be smarter than you. You can't kill demand for something so useful unless you utterly convince a majority that it can not possibly work - here your piracy-analogy holds water again. They may indeed pull a Napster (we've seen how that played out) but I think it's much more likely they would try a very long-term, elaborate stealth attack to erode trust in p2p money systems as a whole. But just as with piracy this seems like a losing proposition. Unless a truly insurmountable flaw is discovered that renders any system with the features of bitcoin infeasible.