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> As soon as a successful attack is announced publicly, faith in Bitcoin will be shaken to badly that nobody will ever want to use anything called "digital cash

> As soon as a successful attack is announced publicly, faith in Bitcoin will be shaken to badly that nobody will ever want to use anything called "digital cash" for a long time. It's worth noting that a 51% attack would only allow double-spending, and it's not something that could be realistically hidden; it would be very obvious what was happening. In addition, the amount of computing power available to the bitcoin network is becoming significant enough that it would be hard to exceed, even with a botnet. It's also worth pointing out that people still use Paypal, despite all the stories of frozen accounts and people never getting their money back. People also still use credit cards, despite not every instance of fraud resulting in the victims getting their money back.

betterunix 14y ago
"In addition, the amount of computing power available to the bitcoin network is becoming significant enough that it would be hard to exceed, even with a botnet." https://en.wikipedia.org/wiki/TICOM https://en.wikipedia.org/wiki/TICOM I agree that people may very well use Bitcoin despite a successful attack (plenty of people still use Hushmail), although I think a lot of confidence would be lost. Bitcoin has a lot of hurdles to overcome as it is, and the detection or announcement of a successful attack would add yet another.
- weavejester 14y ago
  What does TICOM have to do with anything? A 51% attack is a possibility, and might be currently possible with the largest botnets known to exist today, but it would be pushing it. In future it becomes even more difficult.
  - betterunix 14y ago
    That is exactly the sort of argument the Germans made: that Enigma had known cryptographic flaws, but that they did not think anyone would actually expend the effort needed to attack it. You are saying that Bitcoin has a known flaw, but that nobody is going to amass the computing power needed to exploit that flaw. That is a bad way to approach security. It is not just about botnets (CPU "mining" is pretty slow); what do you think stops someone from spending their money on enough ASICs to pull off the attack? It is not all that expensive, maybe tens of millions of dollars in chips. Even if it were hundreds of millions of dollars, if Bitcoin were as threatening to the financial system as some people seem to think it is, that would not be a lot to spend on attacking it. It is also important to recognize that the existence of an obvious polynomial time attack does not in any way rule out the existence of faster attacks, it only establishes an upper bound on the attack effort. The reason proofs of security in modern cryptography involve a reduction to an (assumed) infeasible problem is that it rules out all practical attacks (in fact, all theoretically feasible attacks).
    - weavejester 14y ago
      It would be nice if there were a way of solving the double-spending problem that would make all attacks infeasible. But since there isn't, we need to make do with the options we have: to place trust in either a pre-chosen authority, or a defined majority we assume to be trustworthy. Not all the tools we have for maintaining security are as good as public key encryption or symmetric encryption. In the world of bricks and mortar, $10 million buys you a lot of criminal clout. Is a safe deposit box safe against a determined attacker with that budget? Are all employees immune to million dollar bribes? The law attempts to redress imbalances by making it difficult to get away with circumventing security to perpetrate financial crimes. The problem is not so much stealing from a bank, but getting away with it after the fact. The same problem applies to bitcoin if you want to execute a 51% attack; double-spending is financial fraud, after all. Buying up $10 million worth of ASICs is relatively straightforward, but doing so in a way that can't be traced back to you is substantially more difficult. As well as the problem of trying to run that amount of hardware in secret, without a paper-trail, you'll also have problems in trying to convert any profits you make from the scheme back into fiat currency. If one merely wanted to demonstrate the attack without profitting from it, then one could double-spend a small amount between accounts you own, in the same way that one could demonstrate an attack on a safe by buying one and then drilling into it. But that doesn't change the fact that there's a big difference between circumventing security, and illegally profitting from it without consequences.

betterunix 14y ago

"In addition, the amount of computing power available to the bitcoin network is becoming significant enough that it would be hard to exceed, even with a botnet." https://en.wikipedia.org/wiki/TICOM https://en.wikipedia.org/wiki/TICOM I agree that people may very well use Bitcoin despite a successful attack (plenty of people still use Hushmail), although I think a lot of confidence would be lost. Bitcoin has a lot of hurdles to overcome as it is, and the detection or announcement of a successful attack would add yet another.

weavejester 14y ago
What does TICOM have to do with anything? A 51% attack is a possibility, and might be currently possible with the largest botnets known to exist today, but it would be pushing it. In future it becomes even more difficult.
- betterunix 14y ago
  That is exactly the sort of argument the Germans made: that Enigma had known cryptographic flaws, but that they did not think anyone would actually expend the effort needed to attack it. You are saying that Bitcoin has a known flaw, but that nobody is going to amass the computing power needed to exploit that flaw. That is a bad way to approach security. It is not just about botnets (CPU "mining" is pretty slow); what do you think stops someone from spending their money on enough ASICs to pull off the attack? It is not all that expensive, maybe tens of millions of dollars in chips. Even if it were hundreds of millions of dollars, if Bitcoin were as threatening to the financial system as some people seem to think it is, that would not be a lot to spend on attacking it. It is also important to recognize that the existence of an obvious polynomial time attack does not in any way rule out the existence of faster attacks, it only establishes an upper bound on the attack effort. The reason proofs of security in modern cryptography involve a reduction to an (assumed) infeasible problem is that it rules out all practical attacks (in fact, all theoretically feasible attacks).
  - weavejester 14y ago
    It would be nice if there were a way of solving the double-spending problem that would make all attacks infeasible. But since there isn't, we need to make do with the options we have: to place trust in either a pre-chosen authority, or a defined majority we assume to be trustworthy. Not all the tools we have for maintaining security are as good as public key encryption or symmetric encryption. In the world of bricks and mortar, $10 million buys you a lot of criminal clout. Is a safe deposit box safe against a determined attacker with that budget? Are all employees immune to million dollar bribes? The law attempts to redress imbalances by making it difficult to get away with circumventing security to perpetrate financial crimes. The problem is not so much stealing from a bank, but getting away with it after the fact. The same problem applies to bitcoin if you want to execute a 51% attack; double-spending is financial fraud, after all. Buying up $10 million worth of ASICs is relatively straightforward, but doing so in a way that can't be traced back to you is substantially more difficult. As well as the problem of trying to run that amount of hardware in secret, without a paper-trail, you'll also have problems in trying to convert any profits you make from the scheme back into fiat currency. If one merely wanted to demonstrate the attack without profitting from it, then one could double-spend a small amount between accounts you own, in the same way that one could demonstrate an attack on a safe by buying one and then drilling into it. But that doesn't change the fact that there's a big difference between circumventing security, and illegally profitting from it without consequences.