Bitcoin’s Collusion Problem - by Timothy B Lee

[grondilu]

Stop talking about "the central bank of the bitcoin economy".  There is simply no such thing, apart in your mind.

There could be a large collusion of attackers, but since they would try to disrupt the bitcoin network, there is no way we can call them "the bitcoin central bank".    In a centralised economy, a central bank is supposed to organise and protect the economy, not to destroy it.

[stillfire]

"While network nodes can verify transactions for themselves, the simplified method can be fooled by an attacker's fabricated transactions for as long as the attacker can continue to overpower the network."

A simple solution to that would be for thin clients to randomly verify blocks. Those clients would still be substantially thinner than those checking the whole chain, and finding one bad block would be sufficient to invalidate a whole bad fork. Satoshi also proposed a p2p alert system. Such a system would be slightly vulnerable to spam (someone could try to spread alerts about many blocks) but the worst case outcome would be that all thin clients would temporarily turn into fat clients.

Nothing stops the attacker from overpowering the network except people committed to Bitcoin, making the central bank for the Bitcoin economy subject to populist will (mediated through, of course, the need to purchase and deploy mining hardware and alternative P2P participant software -- it's not "one person one vote," but it's not far from "one dollar one vote").  I'm suggesting that this is a serious and insufficiently recognized problem for a currency meant to be in some sense an alternative.

Obviously if the majority (the 'populist will') switched their clients to do something non-standard they could change the truth of the network. That's what I described in my social attack post. I would not describe that as unrecognised though given that the whole system is founded on the idea of "one CPU, one vote".

[MoonShadow]

Are you refering to the attack vector that requires over 50% of the hashing power of the network, with the intent of overwriting recent blocks?  The forced double spending attack?

It isn't limited to that problem.  Satoshi noted it clearly in his original paper:  "While network nodes can verify transactions for themselves, the simplified method can be fooled by an attacker's fabricated transactions for as long as the attacker can continue to overpower the network."  Nothing stops the attacker from overpowering the network except people committed to Bitcoin, making the central bank for the Bitcoin economy subject to populist will (mediated through, of course, the need to purchase and deploy mining hardware and alternative P2P participant software -- it's not "one person one vote," but it's not far from "one dollar one vote").  I'm suggesting that this is a serious and insufficiently recognized problem for a currency meant to be in some sense an alternative.

I see.  I don't consider this a real problem, even though it is relatively cheap at present.  The big reason is that the network is very young, and the whole value of the currency relatively small; so the primary motivation of such an attacker would be the outright destruction of Bitcoin.  The only group with such a motive would be powerful western central banks and their governments.  No small group, but the rest of the world's governments then have a vested interest in anything that stands to weaken western central banks, which includes relative heavyweights such as Brazil and China.  Also, this attack would have to continue for a significant period of time to actually destroy Bitcoin, and has nearly zero chance of altering any significant portion of the blockchain history.  Savy users are going to suspend their transactions if such an attack were underway, and less savy users are likely to learn about the attack in the media, also suspending transactions.  Suspensionof activities is not the same as abandonment of the currency, and any such attack, even now, is going to require the comitment of sustantial resources.  This would be something that would be hard for government agents to be able to justify to their budget aware leadership for very long, considering that there are much bigger thinkgs in this world for spooks to be throwing processing power at.  In the future, if Bitcoin grows to become a real threat to the status quo, it would also be too big to break.

[grondilu]

The function of the central bank is provided by the network; controlling half the network's hashing power confers the powers of a central bank.  The rest is just semantics, I think.

It seems to me that you miss one point.  The attack that was discussed here doesn't only consist in gathering more than 50% of CPU.

I wouldn't mind if anybody does, as long as he processes transaction correctly.

But in order to use any priviledged power, such a big miner would have to run a modified version of the software, and basically the only thing he could do would be to hurt the network by refusing to process incoming transactions or double spending some.  They could not mint arbitrary amounts of bitcoin, for instance.

So it would not have the powers of a central bank.

[MoonShadow]

The function of the central bank is provided by the network; controlling half the network's hashing power confers the powers of a central bank. 

This is not so.  The function of the Bitcoin network is to be the transaction processing agents (Visa, PayPal, banks) but a central bank does not exist for this function.  The central bank exists to manage a fiat currency, and the management of Bitcoin is in the codebase.  No attack that fails to change a majority of the running codebase of the p2p network has near zero chance of long term success.  All such attacks are either local in scope (double spend, affecting the vendor who is defrauded), limited in time (blockchain fork) or both.  If you can't change the codebase, you can't "manage" the currency, and any changes that you make to the protocol are destroyed after you lose your majority cpu power status.  Which could happen in very short order, as there is an unknown amount of reserve hashing power that could be convinced to come online in defense of the honest network even at a loss.  I am one such person.  If a credible attack of the system were underway, and I was aware of it, I'd be more than willing to hash at a loss.  I'm sure that I'm not alone.

[MoonShadow]

I don't mean to suggest otherwise.  I'm just pointing out that if it's not that hard for a single relatively wealthy individual, much less an organization, to destroy an economy, the economy is probably more ephemeral than people imagine.

And I don't agree with your perspectives upon the implications of such an attack.  As already stated, hijacking the blockchain as a DOS of the network, would not lead to the destruction of the economy.  Such an attack would have to be maintained for some considerable period of time and against a group of honest participants who all have varying degrees of vested interests to negate such an attack, and who are not generally any more idle than the attackers.

[rezin777]

The fragility hasn't seemed to sink in fully.  Surely many understand the conceptual possibility of the attack; I don't mean to suggest otherwise.  I'm just pointing out that if it's not that hard for a single relatively wealthy individual, much less an organization, to destroy an economy, the economy is probably more ephemeral than people imagine.

The depth of the attack doesn't seem to sink in fully for you. If it's not hard, anyone with a bit of brains should have proceeded to initiate an attack at this point. When bitcoins are trading for 1.55 USD each, someone should be motivated? Perhaps you should read the paper again.

[stillfire]

A government hostile to Bitcoin doesn't need to stamp out P2P technologies generally; it just needs to deny service to Bitcoin by taking it over.

The fragility hasn't seemed to sink in fully.  Surely many understand the conceptual possibility of the attack; I don't mean to suggest otherwise.  I'm just pointing out that if it's not that hard for a single relatively wealthy individual, much less an organization, to destroy an economy, the economy is probably more ephemeral than people imagine.

I can agree that the risks for this system are greater than imagined by those investing heavily at this time. Yet I maintain that people in this community are too concerned about technical attacks such as the 'NSA with supercomputers'. Post after post is made with back-of-the-envelope calculations regarding the amount of CPU power needed to take BitCoin off course. All the while the social aspect is overlooked.

Long before something like that would happen, an opposing government would do what governments do best. They'd make law and sway opinions. That's how the government defeated the gold as a currency and acquired the coveted magic wand of inflation. At no point did they try to invent fake gold, or physically destroy it. They just slowly displaced it, made it 'unpatriotic' not to play along, until fiat money won. In the US in 1933 they even forbade private ownership in larger quantities of gold.

Similarly BitCoin would first be heavily regulated, starting at the points of sale, all the while populist propaganda made such action appear tremendously beneficial to society. Then eventually enough control would be held over not just the network but more importantly the popular merchants that the de facto power over the network would rest with the government. Badcoins, registration requirements and mandatory inflationary systems would follow.

That is how I foresee the end of it. You have not convinced me the technical risks you describe won't be easily countered through coordinated effort of the community vested in preserving the value of the BitCoin. And even if you had me so convinced, I would still fear the imposition of monetary control through legal and social means much more greatly.

[MoonShadow]

Long before something like that would happen, an opposing government would do what governments do best. They'd make law and sway opinions. That's how the government defeated the gold as a currency and acquired the coveted magic wand of inflation. At no point did they try to invent fake gold, or physically destroy it. They just slowly displaced it, made it 'unpatriotic' not to play along, until fiat money won. In the US in 1933 they even forbade private ownership in larger quantities of gold.

Although I agree that social engineering is the greater risk for Bitcoin, I don't agree that governments can do to Bitcoin what it did to hard money.  First, they don't have that kind of time.  Bitcoin is maturing faster then supporters expected, and if it gets anywhere near the mindshare of PayPal, the public would call 'bullshit' on any kind of propaganda that any government agents might produce.  Bitcoin is running on Internet time, governments cannot.

This also isn't 1933, and the public might call 'bullshit' on it anyway; since we all have the truth button only a click away, and the young are inclined to use that button a hundred times a day.  Any mention of the term "Bitcoin" by any government agency or representative might just have the opposite of the intended effect.

[MoonShadow]

It's just hard to imagine the reserve hashing power more than, say, doubling the existing "committed" hashing power.

Hard to say.  In fact, impossible to say.  But I would guess that you are correct, at present.  As hashing becomes ever more marginal on a straight for-profit basis, and the user base continues to grow, the reserve hashing power will continue to climb.  If there were some way to estimate the number of non-generating nodes, we might be able to take a fair guess at the reserve capacity; but as far as I know, there is no credible way to count non-generating nodes.

but I think the reason is just that nobody cares to mount such an attack so far. 

Oh, certainly not.  There has been many before you who have come up with variations on the basic 'overpower the network' attack.  None of which have proven to be particularly advantagous.  I encourage you to keep thinking about attacking the network, however, because if one of us can think of a vector of attack before a hostile entity does, we can mitigate such an attack.

It's only a few thousand people participating,

How do you know that?

I believe, as a side note, that some of my math earlier in this thread is off by a decimal place, as I promised it would be.   I should be saying $1,000,000 at today's statistics, not $100,000.  But that's still petty change to a regulator, and notably it's far less than the market capitalization of Bitcoin.  Again, importantly, the cost of the attack grows only proportionally to the hashing power of the network.  Also, that's just the acquisition cost; the hardware could be resold or reused after the attack achieves its purpose.

I still think your numbers are off.  How are you coming up with this estimate?  Are you including the ongoing costs of power?  Are you considering the islanding effects of Tor and I2P?  Have you considered possible countermeasures that the Bitcoin network could actively respond with?  Have you considered the possible actions of other governments generally hostile to whatever government happens to be hostile to Bitcoin?

[rezin777]

I say this as someone deeply impressed with the design of the protocol and the software, but I think the reason is just that nobody cares to mount such an attack so far.  It's only a few thousand people participating, and the Bitcoin economy doesn't really have even $9 million in it (that's just the market capitalization - the clearing price multiplied by the number of Bitcoins); even if it did, that still wouldn't be worth most governments' time.  A small-scale protest in San Francisco costs more and involves more people than Bitcoin does at this stage.

And I doubt anyone's yet using Bitcoins for anything that authorities care about, really; if it's being used to trade only a bit of LSD or child pornography, law-enforcement resources likely won't divert toward that use when there's much lower-hanging fruit.  This is what I mean by saying that there's a bootstrapping challenge that Bitcoin hasn't faced yet: the challenge is how to resist populist pressure when that populist pressure can directly destroy it, for technical reasons -- not just politically or through external enforcement actions.

I do wish you would stop pontificating about the weaknesses or flaws of the bitcoin network and either attack it directly or promote something superior. Otherwise you come across as nothing more than an educated troll.

Where do your motives lie sir?

[kiba]

Garnishing about the 50% hashing power is boo-ring and  been covered a thousand time.

[grondilu]

I do wish you would stop pontificating about the weaknesses or flaws of the bitcoin network and either attack it directly or promote something superior. Otherwise you come across as nothing more than an educated troll.

Where do your motives lie sir?

I don't understand this sort of personal attack and find it extremely annoying and distracting.  I'm offering analysis.  My motives aren't relevant, but I've already expressed my view as (1) impressed, (2) practically skeptical, and (3) morally skeptical.  I don't have to commit to pay significant money to mount an attack myself in order to point out that it's easier for others to do it than it typically supposed, nor do I have anything superior I'm interested in promoting.  I can't stand the overuse of the word "troll" in these contexts; it's just extraordinarily annoying schoolyard-type bullying.  Save the bitterness for people who are actually doing something objectionable, please, and simply ignore an analytical argument if you don't find it interesting or helpful.  I suppose I should be happy that at least you consider me "educated." 

You said that whether or not calling a group of attackers a bitcoin "central bank"  was just a matter of semantics and was not relevant.

I could as well argue that calling you a troll is just a matter of semantics too.

[rezin777]

I can't stand the overuse of the word "troll" in these contexts; it's just extraordinarily annoying schoolyard-type bullying.  Save the bitterness for people who are actually doing something objectionable, please, and simply ignore an analytical argument if you don't find it interesting or helpful. 

If you don't want to be called a troll, don't make such trollish suggestions.

if it's being used to trade only a bit of LSD or child pornography

There is a wealth of intelligent people on this forum finding new and interesting ways to trade and promote bitcoin and this is what you come up with?

[goatpig]

You're clearly not interested in paying attention to the substance of what I'm saying, so I'm done here.  The tone and pseudointellectual disposition of most of the people on this forum are absurd; it's like speaking to 17-year-old libertarians who think they're geniuses or mentally ill Randists who see themselves as underappreciated innovators.  You're just not reading what I'm saying, and you're quoting isolated fragments out of context to confirm some view you have of me that's entirely incorrect and unfounded.

Far more intelligent commentary about the economics and social forces that affect Bitcoin is available at external forums, for anyone interested in speaking to adult-minded people about the topic.  For example, see the following thread, which anticipated most of the discussions I've had here (including my own comments) by several months:  http://www.bogleheads.org/forum/viewtopic.php?p=959393.

That's how adults talk about the topic, rather than unimaginative followers who think they're innovators or people who don't know how to read.  I was pointing out an analytical approach you could learn from; you chose to ignore it.  Bye.

Lemme understand one thing: Do you picture Bitcoin adopters as stupid in general? If I look at the logic here, you are coming in this forum presenting Bitcoin as inefficient and crippled with gaping security flaws. This implies you think any adopter is at least hasty in decision making and/or poorly informed of the mechanics of this project. You are thus naturally prejudiced against this community.

Your bitter, repetitive comments about Libertarians are proof enough, yet it is interesting that you won't acknowledge the same right to prejudice to the Bitcoin community against your kind of outside contributor even though you use this very prejudice to legitimate your answer to those who contradict you in the threads you participate. Not much for respect, is there?

Have you considered the possibility that as an outsider, you are the one that is less informed, than let's say, founding and early members of this project? Have you also considered that your grasp of the technology used in this project is not at the stellar level you're fancying it? I giggled when you mentioned using a DOS attack on a p2p project...

Lastly, have you considered that suggestions detached from reality, the persistent speculation on Bitcoin's flaws resting on nothing but conjecture is simply tiring the contributors of this thread? What proper discussion can you expect by linking to threads outside this community. How can you expect decent defense of this project's technological choices by discussing it with people that have no involvement nor experience with it? And you label that an adult-minded discussion? And then you're surprised you're called a troll?

[goatpig]

One last comment, just on the chance that there might be some progress here:

Your "giggling" is immature and misinformed, because you're not actually reading what I'm saying and instead assuming that I'm saying incorrect things.  Maybe other people often say incorrect things, and backed by Bayesian probability you're jumping to the assumption that I'm one of those people, but I'm not.

If you think Bitcoin is not subject to a denial-of-service attack just because it's a peer-to-peer network, reread Satoshi's paper, which explicitly points out the DOS opportunity.  Or believe Gavin, who has said "Bitcoin's p2p network is subject to various kinds of denial of service attacks. There, I said it," and "Bitcoin is still vulnerable to DOS attacks.  I'm not sure anybody knows how to prevent DOS attacks on a p2p network that allows untrusted/unverified peers to join."  That's the same point as mine, which is that the openness of Bitcoin's network is not just a strength but also a weakness.

I never even claimed that I'm saying anything new, here, about a DOS attack against Bitcoin.  What I've said is that the attack is cheaper, in the present situation, than many people seem to think, and that the cost does not necessarily relate -- in the real world, rather than a hypothetical frictionless market -- to the capitalization of the Bitcoin market.

Nobody's actually said that's wrong.  But immature people call that a "trolling" comment, and you in particular seem to be incapable of reading what I'm saying rather than just making incorrect assumptions about it.  I don't know if it's a bad attitude, a reading-comprehension problem in English (your syntax and style strike me as natively French, for what it's worth), or just immaturity, but it's counterproductive to real people trying to offer real analysis.  You don't have to believe me, but my contributions to open-source software go back more than 10 years, and I have designed significant cryptography-based security systems; I'm likely more experienced in these matters than Gavin, though of course not nearly as committed to the project.  And nobody here has given me any reason to be.  The social community behind a project is quite important to me; I already have more than enough money and recognition, which is why I'm contributing pseudonymously.  (I am not, like apparently many here, someone who has been marginalized by the existing economy.)

Note, again, that Gavin is not disagreeing with anything I'm saying here; he's made the technical point himself before, and I'm just adding the economic observation that the (already recognized) attack is relatively inexpensive, both in real-world terms and as a matter of proportionality to the market capitalization of the Bitcoin economy.

Nice one on the French part, you're on spot. The reading comprehension part is funny coming from someone that makes a point of not being rigorous with semantics...

As for attacks on p2p projects, countless failed attempts by commercial firms, backed by the financial power of the movie, music and video gaming industry, to DOS torrent trackers and inject false packets in the last 5 years or so speaks volumes about the counters a p2p network has against such basic attacks, which are nothing more than harassment. There's also quite a history of DOS and other petty attacks on mining pools in this very forum, there is a documented case of forking available too, yet this project doesn't look to me like it's on the brink of extinction.

You don't have to believe me

No I don't, and I said before, since you're making a point of being anonymous, this is idle talk. It also shows you have issues presenting the veracity of your points without resorting to credentials.

I am not, like apparently many here, someone who has been marginalized by the existing economy.

Spoken like a true central banking jingoist?

and I'm just adding the economic observation that the (already recognized) attack is relatively inexpensive, both in real-world terms and as a matter of proportionality to the market capitalization of the Bitcoin economy.

First of all, if an attack is easy to perform, a truly concerned party would present an isolated experiment reproducing it instead of speaking of conjecture. Second, such declarations and the weight they carry gives the right to the contributors of this post to ask about your motives, but somehow you brush those as irrelevant. And lastly, your point isn't realistic. What you are saying is akin to presenting society as fragile because a detractor of said society can walk in the streets shooting people dead for the price of a single gun.

[MoonShadow]

@s

This is an open forum, and you get into a flame war with one member.  And then paint the entire membership with the same wide brush.  If you have something to contribute to the community, please stay.  But if you really are a 10+ year veteran of this field of study, then you should have thicker skin than this.  Your assesment that this forum is dominated by teenaged libertarians is likely correct, but irrelevent.  I was annoyed by that comment, because you used the phrase as an insult, implying that teenagers or libertarians are contemptable in some fashion.  I've known enough of both to know that is not a rational perspective.

I've been following this thread, and have yet to see either of you post any significant personal attack.  If Goatpig annoys you, ignore him.

[goatpig]

@s

This is an open forum, and you get into a flame war with one member.  And then paint the entire membership with the same wide brush.  If you have something to contribute to the community, please stay.  But if you really are a 10+ year veteran of this field of study, then you should have thicker skin than this.  Your assesment that this forum is dominated by teenaged libertarians is likely correct, but irrelevent.  I was annoyed by that comment, because you used the phrase as an insult, implying that teenagers or libertarians are contemptable in some fashion.  I've known enough of both to know that is not a rational perspective.

I've been following this thread, and have yet to see either of you post any significant personal attack.  If Goatpig annoys you, ignore him.

but but, he called me French ='(

[MoonShadow]

@s

This is an open forum, and you get into a flame war with one member.  And then paint the entire membership with the same wide brush.  If you have something to contribute to the community, please stay.  But if you really are a 10+ year veteran of this field of study, then you should have thicker skin than this.  Your assesment that this forum is dominated by teenaged libertarians is likely correct, but irrelevent.  I was annoyed by that comment, because you used the phrase as an insult, implying that teenagers or libertarians are contemptable in some fashion.  I've known enough of both to know that is not a rational perspective.

I've been following this thread, and have yet to see either of you post any significant personal attack.  If Goatpig annoys you, ignore him.

but but, he called me French ='(

Even your smiley makes me think of a mime.

[theymos]

If someone makes Bitcoin unusable for a long time by controlling >50% of the network, people might start weighting the "work" value of a chain by looking at its behavior in handling transactions. A chain of 20 blocks with no transactions is very likely to be malicious, for example. As long as it's done by weighting instead of outright rejection, legitimate clients shouldn't ever stay on separate chains for long.