Here's previous comments about what quantum computing really is: Informative!

D-Wave has always been known to be full of $#!+ when it comes to quantum computers. They've never demonstrated entanglement in their QCs which pretty much makes this a classical computer with a different medium for pushing information around. That's not to say that their research is complete shit. They are pioneering better ways to control qubits. But actual quantum computers are a major threat to modern day cryptography, and this "quantum computer" doesn't concern me at all.

I'm really tired of hearing the same Bitcoin-is-worthless jargon coming out of /. on every Bitcoin headline. And it's not like there's a Bitcoin story every day... it's once every couple months, so you can't really be getting "sick" of it...

People can argue all they want about economic theory and fiat currency, intrinsic value, etc. But the fact is that Bitcoin has had value >=$1/BTC for over a year now. And it's growing. When the speculator bubble burst, everyone thought for sure that was the end of it. But what really happened was that the speculators got out of the game, and now Bitcoin is progressing much more naturally... and so far it's been successful.

I don't care what your economic theories are: Bitcoin still exists and is used for online commerce. I don't care whether you think it's worthless: they have clearly demonstrated they are not worthless, and in fact have very non-negligible value to a great very many people. I don't care whether you think the gold-standard was a bad idea, or whether Bitcoin is a commodity or a currency: Bitcoin is thriving and has been thriving for a long time. There's still plenty of questions left to be answered about Bitcoin and its place in society, politics and economics. But one fact remains: Bitcoin itself is empirical evidence that all your theories about whether it should, could or will remain valuable, may not be accurate. That's not to say there's no truth at all in your arguments. But Bitcoin is a truly novel, one-of-a-kind thing, and it has demonstrated more than just being worthless-bits, simply by the fact that it not only still exists, but that it is thriving.

And geezuz: I thought /. was about geeks. Bitcoin should be a popular topic here, as it represents online freedom, cryptography, politics, economics, computing, and networking all in one big, brilliant mess of bits -- basically everything everyone loves talking about, here. Even if you think the currency will crash tomorrow, it should still be a fascinating topic, hardly worth the intransigent beatings that it receives on every slashdot story.

I took a class on Quantum computing, and studied many specific QC algorithms, so I know a little bit about them.

Quantum Computers are not super-computers. On a bit-for-bit (or qubit-for-qubit) scale, they're not necessarily faster than regular computers, they just process info differently. Since information is stored in a quantum "superposition" of states, as opposed to a deterministic state like regular computers, the qubits exhibit quantum interference when mixed with other qubits. Typically, your qubit starts in 50% '0' and 50% '1', and thus when you measure it, you get a 50% chance of it being one or the other (and then it assumes that state). But if you don't measure, and push it through quantum circuits allowing them to interact with other qubits, you get the quantum phases to interfere and cancel out. If you are damned smart (as I realized you have to be, to design QC algorithms), you can figure out creative ways to encode your problem into qubits, and use the interference to cancel out the information you don't want, and leave the information you do want.

For instance, some calculations will start with the 50/50 qubit above, and end with 99% '0' and 1% '1' at the end of the calculation, or vice versa, depending on the answer. Then you've got a 99% chance of getting the right answer. If you run the calculation twice, you have a 99.99% chance of measuring the correct answer. However, the details of these circuits which perform quantum algorithms are extremely non-intuitive to most people, even those who study it. I found it to require an amazing degree of creativity, to figure out how leverage quantum interference constructively.

But what does this get us? Well it turns out that quantum computers can run anything a classical computer can do, and such algorithms can be written identically if you really wanted to, but doing so gets the same results as the classical computer (i.e. same order of growth). But, the smart people who have been publishing papers about this for the past 20 years have been finding new ways to combine qubits, to take advantage of nature of certain problems (usually deep, pure-math concepts), to achieve better orders of growth than possible on a classical computer. For instance, factoring large numbers is difficult on classical computers, which is why RSA/PGP/GPG/PKI/SSL is secure. It's order of growth is e^( n^(1/3) ). It's not quite exponential, but it's still prohibitive. It turns out that Shor figured out how to get it to n^2 on a quantum computer (which is the same order of growth as decrypting with the private key on a classical computer!). Strangely, trying to guess someone's encryption key, normally O(n) on classical computers (where n is the number of possible keys encryption keys) it's only O(sqrt(n)) on QCs using Grover's algorithm. Weird (but sqrt(n) is still usually too big).

There's a vast number of other problems for which efficient quantum algorithms have been found. Unfortunately, a lot of these problems aren't particularly useful in real life (besides to the curious pure-mathematician). A lot of them are better, but not phenomenal. Like verifying that two sparse matrices were mulitplied correctly has order of growth n^(7/3) on a classical computer, n^(5/3) on a quantum computer. You can find a pretty extensive list by googling "quantum algorithm zoo." But the reality is that "most" problems we face in computer science do not benefit from quantum computers. In these cases, they are no better than a classical computer. But for problems like integer factorization, bringing the compute requirements down to polynomial time isn't just faster: it makes a problem solvable that wasn't before.

Unfortunately [for humanity], there is no evidence yet that quantum computers will solve NP-complete problems efficiently. Most likely, they won't. So don't get your hopes up about solving the traveling salesmen problem any time soon. But there is still a lot of cool stuff we can do with them. In fact, the theory is so far ahead of the technology, that we're anxiously waiting for breakthroughs like this, so we can start plugging problems through known algorithms.

Have you ever heard of the Underhanded C Contest. You get points for making the code exhibit some kind of backdoor, extra points for the more it looks like it could've been an innocent mistake (for instance, code where using a less-than-or-equal-to operator instead of less-than operator actually opens up an obscure security hole, and it's a mistake programmers make all the time).

I recommend you look at some of the examples of winning entries. It's amazing what these people have come up with. No number of eyes will find it. Simply put, even if it's a popular open-source project, thousands of eyes are likely to miss a well-placed backdoor like these. And if anyone is capable of doing it, the NSA certainly is.

Still don't believe me? How about the OpenSSH PRNG flaw that went unnoticed for two years, despite being used in servers all over the world. It was due to someone removing what appeared to be a useless line of code, but that code was actually adding some necessary extra entropy to the random number generator. It might've been an accident, or malicious. But the point is it happened, and on a high-profile project.

Shame on you slashdot. This is a disgustingly misleading headline that has absolutely nothing to do with the paper. The paper is only offering recommendations for the future, based on some incorrect assumptions about the network (which is that there will be difficulty in propagating transactions). This is not a "flaw" in the protocol.

The Bitcoin network is well-connected and the only nodes that have incentive not to forward txs make up a tiny percentage of the network (less than 1%). Even if they were the only nodes on the network, the network is designed so that users can locate them, and it costs nothing for a user to forward their transaction to many/all of them. This is completely a non-issue.

Someone purchases X BTC from an exchange, donates it to Wikileaks anonymously and easily. Wikileaks then sells X BTC to an exchange -- or if there is a problem with official bank transfers, I'm sure they can sell to investors who would be happy to buy for 10% off. In the end, Wiki leaks gets the 90%*X*exchangerate, which is dramatically better than the 95% loss due to income due to gov't/bank freezes on assets and transfers. The volatility risk is only in the time between when they receive the BTC and when they sell it, which is a very short time given how fast BTC transactions can happen.

Bitcoin has some intrinsic value -- but unfortunately, most of this value has the most impact on those doing illegal or unethical things. The ability to control and move them across the globe, nearly instantaneously, with no restrictions or fees, and without the ability of any government/bank to stop/freeze it, has produced quite a market for it (and it can be anonymous if you know what you're doing). You say it has no value, but what about Wikileaks who have had 95% of their assets and income cut off by governments and banks freezing their money. They'd still be 100% functional if they were dealing in BTC. And of course, the drug trade benefits too. These aren't the most "ethical" reasons for it to have value, but they don't have to be good reasons to impart actual value. The fact is, there are people who want BTC, and as long as there's a scarce amount of it, it's going to acquire value in the minds of some. (BTW, I have no interest in these unethical properties, I'm all for BTC because of the fact I have control over it, and don't have to pay anyone or give out any information to use it).

To those arguing about bubbles -- I'm interested to see how this exactly looks like a bubble. Bubbles burst, BTC didn't. The fact is there's still lots of people involved in BTC, there just happens to be more people selling than buying, which is why the prices has declined slowly over months... it didn't just collapse in a week like most bubbles.

Personally, I'm happy to see all the speculators get out of BTC, and hopefully it can maintain some degree of stability now without all the gambling. Unfortunately, botnets and Trojans like this are probably the biggest reason for the price decline, as their constant sell-off causes negative pressure on the prices. But what is interesting is that so far no one has actually succeeded at attacking the protocol itself. Sure, individual websites/exchanges get attacked, but the protocol itself remains secure. I think it's worth something that the botnet owners have decided to play by the rules of BTC... because if they could break the system to make a quick buck, they would. But so far there has been $20,000,000+ worth of value in the BTC for many months, which is plenty incentive for every unethical person in the world to break it--yet no one has.

I'm not convinced that Bitcoin 1.0 (right now) will survive the test of time. It's security is great, but it's name has been soiled, and some lessons learned really need to be applied, but cannot be once the beast is set in motion. I wouldn't be surprised if it stuck around for a while, but even if it doesn't, something else will replace it. There's too much value in "freedom-enhancing" currencies, and there's no doubt that Bitcoin has been a proof-of-concept for it that it works.

P.S. - Bitcoin really shouldn't be referred to as a "currency." It's more like a commodity, similar to gold, since there is a finite amount of it in the world. If BTC is going to survive the legal battles, it would be best for its supporters to not fight for it as a currency, as that can open it up to all kinds of legal attacks.

Guys... what did you expect? Nobody supports pot legalization more than me, but publicly supporting it as acting or candidate president is still suicide in today's politics. You can complain all you want, but that doesn't mean Obama is going to suddenly turn around and support an issue that is likely to destroy his chances of re-election. If you've been paying attention to politics at all, ever, you'd know that "politically correct" is not even close to the same as "correct." You have no choice but to play the politics game once you're in the game. This statement/response is part of that game.

Of course I whole-heartedly disagree with this statement, but show me one presidential candidate who publicly supports pot legalization and has a tangible chance of being elected. That politician has never existed. I assure you, Obama actually believes pot should be legal. As do hundreds of other politicians out there. But the solution (for the politician) is not to sacrifice their job to admit he believes in legalization, until the population is ready is ready for it. The real solution (for the constituents) is getting people in the population educated on the matter to the point that it actually becomes acceptable for a major politician to support it. This isn't Obama's problem... it's our problem. I only wish we had a better education system that encouraged people to think for themselves, instead of just believing everything they heard the first time.

I have been writing BTC software for the past couple months as well as studying the cryptography behind it. One thing BTC has going for it is that it's remarkably secure given that it's decentralized. The price drop is more to do with lack of interest (and probably dumping by botnet owners who mine only to sell them). This leaves two possibilities:

(1) BTC has a chance to continue to be used, and catch on again later, when its merits have been demonstrated through simple longevity. If, in two years, there still has not been a successful attack on the network, people can mess around with it without feeling like they're taking a huge risk.
(2) The proof of concept is done. Whether BTC itself survives, or there is some new, related cryptocurrency, Bitcoin itself proved that such a decentralized system can exist. I fully believe that something like BTC will prevail in the future, whether it's BTC itself or not. In a world where people are craving less gov't and less big banks/money, I think there is a lot of desire for a decentralized, secure currency.

I think it's major downfall was the lack of usability by regular users -- which is why I set out to write my own software. The core developers did a great job with protocol and security, but it was never usable by non tech-savvy people who were only mildly interested. I still have grand plans for how to bring all the features of BTC to the general public without requiring waiting 24 hours for the blockchain to download, and with the ability to easily encrypt wallets and keep BTC safe offline. It was only recently that the core developers were able to get wallet-encryption implemented, but it was way too late--after a string of high-profile attacks and thefts caused negative PR and massive loss of interest in the currency.

Something like BTC will exist in the future. And I think the system that succeeds will be one in which both the protocol is secure and the system is usable by Joe the Plumber.

Who is posting on slashdot who has 2500 friends?! Wait, does anyone have 2500 friends besides 16 year-old girls on facebook?

I fail to see how this has any impact on the BTC network stability -- in fact, they're only helping to make the network more secure. The only known vulnerability in the network is the threat of someone being able to write blocks faster than all the other non-cooperating nodes, which means single-handedly controlling more than 50% of the entire global bitcoin computation. The more miners there are, the harder this is.

The more direct threat here is if the botnet itself approaches 50%+ of the network. But as it is, the global computation rate is high enough that you'd probably need a few million computers in your botnet to even get to the same order of magnitude as the rest of the network.

As for complaints about "illegal bitcoins," there's nothing to see here. Do people lose confidence in USD everytime someone robs a bank because there are "illegal" dollars in the wild? No, money is money, bitcoins are bitcoins. The problem/illegal part was the person robbing the bank or unauthorized access to people's computers to create a botnet. They're still legit Bitcoins. The only threat to the network is as someone else said: the people controlling the infected computers are probably dumping the coins on the market right away to convert it to cash, which will lower the price slowly over time. And other miners (like myself) will make a few less milli-BTC per day for our watts...

You can find statistical holes in casino games, too. The difference is, the state doesn't kick you out if you win too much.