Topic: Understanding Public and Private Keys (Read 2219 times)

That is not true.  Quantum Computers need an efficient quantum algorithm.  Shor's algorithm is very effective at brute forcing public key systems (RSA, DSA, ECDSA).  They don't significantly reduce the security of symmetric (AES) cryptography or hashing algorithms (SHA-256).

Anything possible eventually will become probable, given time.   

"Some people" here.

BTW: I never said that. But, the scientific community is much more open and transparent now than it every was. This is because people know that sharing research helps the greater whole.

Is it possible that the NSA has built a quantum computer, sure. The real question is, is it probable?

Not to get too abstract, but there are many on this Earth who claim there is technology that exists that goes beyond anything we thought possible for this time period, whether it be alien or not, it is almost certain that there are technologies kept secret which are not revealed publicly.

I find it irritating how some people in this forum seem to think there is nothing in the world that they don't know of or haven't heard of.

Are you referring to the D-Wave? It is far from a general usage computer. Also, very few people have agreed it actually is a quantum computer.

From what I read it is all research and theory at this time. That whole super conductor issues has to be solved first.

There might be some very very small tests that have been done. But, they have a long way to go before there are any practical uses of quantum computing.

But, still my point stands. If a quantom computers start to exist, then pretty much all crypto will have to move to them, not just crypto currency.

How can you say it won't happen in your lifetime? Google and NASA are already using quantum computers, aren't they?

Ha... that's funny. Of course, you can't compare impossible to improbable.

The next time you walk outside you might be approached by an alien robot disguised as a semi-truck too.

Theoretically, quantum computers will render all current cryptography insecure. That includes AES, RSA, SHA, SAH256, Blowfish, etc. The underpinnings of SSL, bank security and others.

Frankly, I don't think it will happen in my lifetime.

Sorry, that was surely really badly put. But the next time he generates a new address, he might just generate the private key that corresponds to the address where Satoshi has the most bitcoins.

I would not want to create any more confusion with these things of course...

What you wrote made no sense. I recommend that you learn the difference between an "address" and a "wallet".

Well, quantum computers are not a high-speed ordinary computers but completely different. Powerful quantum computers would be a threat to Bitcoin, but the main threat would be to the public key cryptography used in bitcoin. The elliptic curve discrete logarithm problem can be quite efficiently solved with a quantum computer using an algorithm similar to Shor's algorithm for prime factorization, and would allow private keys to be recovered from public keys.

But at the current state of quantum computing the risk is only theoretical, Shor's algorithm has been run on quantum computers to factor numbers like 15, which is a nice proof of concept but hardly a threat to any cryptosystems.

In the future, the algorithms in Bitcoin will probably have to be changed into quantum-resistant ones, but there will be a lot of time to think about that. For sure we will see wonderful things in cryptography in the future, maybe it is possible to find some kind of provably very strong cryptography; maybe it is even possible to prove the nonexistence of a really efficient (whatever that means) algorithm at some point. Of course these are hard things, just look at the P=NP problem, but I believe this will be one area of science to see unbelievable progress in the near future. Anyway we will almost surely not see a sudden collapse of present-day crypto, but a gradual weakening and replacement.

Macarena's coming back, I'm sure of that.  


um...what if someone in the future got a quantum computer to continually generate new private keys and check their balance in the blockchain.

Well, the chance of some two people having generated the same key is bigger, and that is needed for collision. The chance is still low enough to be neglected. But to answer OP, yes it is possible that the next time you generate an address with your client, you get the key to Satoshi's main wallet and can use his coins. But the chance is really small. Not like winning the lottery, more like the event that you win the lottery this week and your brother wins it the next week and then the both of you get shot while shopping for groceries in two seemingly unrelated killing sprees and then the killers share the next week's lottery jackpot and Macarena regains its popularity and becomes the numbers one hit on major radio stations, and before that a bitcoin whale reading this message thinks it was the best and most inspiring thing he ever read and contacts me and sends me 500 bitcoins because he was so impressed, you know, that sort of thing.

I'd like to bring this topic into the light again, and ask about quantum computers as a threat to the security of cryptocurrency.
Isn't it more than likely that quantum computers, when developed sufficiently would have no problem at all discovering or cracking bitcoin private keys?
The computing power of quantum computers is awesome and will only get more awesome with development.

Couldn't they also dominate mining as well?

ah!, got it!. thanks! 

No, think about a file that you encrypt and send to their server. It can only be decrypted with a password only you know. So they take care of the file, but if you forget the password, they cant help you. That way they private keys are stored online but only encrypted. When you want to do something on blockchain.info you login, the browser downloads the encrypted file and decrypts it on your computer. That way your private keys are not decrypted online.

Yes locally. You can inspect the cookies. There is a cookie that remembers your wallet id. that has nothing to do with the encryption.

But, other than that, the blockchain.info wallet is all javascript that runs locally. It uses the blockchain.info API to get your balances and to send money. You can view the blockchain wallet source code on github.

locally? are you pointing at cookies?

Yes, the blockchain.info mywallet "server" never knows your PK's, the wallet in encrypted in your browser locally and then uploaded to their server. You can also use a secondary password which means the password your wallet in encrypted with is different than the password that you login with to d/l your wallet.