Quote from: hatshepsut93 on December 14, 2017, 01:08:53 AM

But I think my question can be repeated for wallet seeds: how long would 128 bit seeds be secure against QC, and how do you think Bitcoin community will react if/when someone will start claiming coins from those wallets that were considered to be lost (I'm assuming that most holders will move their funds to new wallets before quantum brute force will become feasible). Of course it's a far smaller threat than the complete failure of public key cryptography, but still I'm curious.

The seeds are run through a KDF (key derivation function) which uses iterated hashing. I am not qualified to say definitively whether a quantum computer could efficiently attack those; and I should know better than to even hazard a guess, without really thinking about it for a very long time. But my gut says this would probably not be a profitable attack. Now, watch someone else show me up here...

Quote from: SpeedRacerF1 on December 12, 2017, 04:27:14 AM

No. Quantum theory is fake "science" and does not exist, nor do "quantum computers".

Quote from: SpeedRacerF1 on December 12, 2017, 04:29:56 AM

quantum mysticism. haha

Quote from: Noctis Connor on December 14, 2017, 02:32:52 AM

You're mad bro, this thing exist. you need to read it here http://www.wired.co.uk/article/d-wave-2000q-quantum-computer Quantom does really exist but it cost a lot of fortune in it.

Quote from: hasmukh_rawal on December 14, 2017, 04:03:50 AM

You must be tripping heavy to live in that imaginary world. The quantum theory as well as the quantum computer both are real and working.
D-Wave was the first company to officially build a quantum computer. You can read it out on Wikipedia here https://en.wikipedia.org/wiki/D-Wave_Systems . Also Google and NASA are joining hands to build a quantum computer which would be much powerful and can solve a problem 100 million times faster than a standard computer.
Take a read about it here : http://www.popularmechanics.com/technology/gadgets/a18475/google-nasa-d-wave-quantum-computer/

There is a pernicious little subcultural strain of arrogant doofuses who enjoy spouting skepticism of quantum mechanics. Put that aside; of course, theyre moronsand all the moreso, when they make Internet posts using computers which could not be built without the practical application of quantum mechanics. Rather like Flat Earthers who use GPS.

There is a huge difference between that, and skepticism of quantum computers. A quantum computer is not a sure thing!

I should preface this by saying, Im not endorsing the opinions of Scott Aaronson. Im only citing him as someone who is not a moron, and wrote a book on quantum computing (which I have not read). I seem to recall some wager on his blog over the (im)possibility of quantum computing, but I cant find it right now; anyway, D-Wave has a long history (2013) of drawing his ire (2017), to say the least.

See how he discusses skepticism of quantum computers:

Quote

What I did is to write out every skeptical argument against the possibility of quantum computing that I could think of. We'll just go through them, and make commentary along the way. Let me just start by saying that my point of view has always been rather simple: it's entirely conceivable that quantum computing is impossible for some fundamental reason. If so, then that's by far the most exciting thing that could happen for us. That would be much more interesting than if quantum computing were possible, because it changes our understanding of physics. To have a quantum computer capable of factoring 10000-digit integers is the relatively boring outcome -- the outcome that we'd expect based on the theories we already have.

Though hes not a good speaker, an interesting lay-level talk is What Quantum Computing Isnt (August 2017). At 09:39, he notes, The trouble is, if you want it to be useful, well, at some point youve got to observe your computer, you know, to read an answer out. And if you just measure, you know, the superposition of all answers, not having done anything else, the laws of quantum mechanics say that what youre going to see will be a random answer. Okay? Well, if you just wanted a random answer, then you could have picked one yourself, with a lot less trouble. (Audience laughs.) Funnily enough, at 12:55, QUANTUM BITCOIN appears on the screen on a slide discussing Silicon Valley Startup QUANTUM buzzwords. He does say of quantum computing that its not science fiction (13:15), when discussing Googles 22-qubit chip; near the end (14:17), he says, Already within a few years, we may achieve what I think of as the number-one application of quantum computing, which is just to disprove the people who say that its impossible. (Audience laughs.) Could it be impossible for some deep reason that nobody has figured out yet? Well, of course. But in some sense, thats the more exciting possibility. Because thats the possibility that means we have to rewrite all the physics textbooks.

Aside, just to cut through some more of the quantum hype:

djb derides the alleged physical security of quantum cryptography (PDF) (Is the security of quantum cryptography guaranteed by the laws of physics? djbs answer seems to be hahaha!). (To be clear, quantum cryptography is a different matter than quantum computing.) He has also attacked the motives of quantum computing and quantum cryptography researchers (How quantum cryptographers are stealing a quarter of a billion Euros from the European Commission. #qkd #quantumcrypto #quantummanifesto). Hmmm.

As for myself, I account myself moderately skeptical of quantum computing; Ill believe it when I see it, but meanwhile I think its a good idea to move to PQ crypto. I would be more surprised if quantum cryptography can deliver on its promises. I dont like the hype around any of it, especially when its sometimes used to FUD Bitcoin.