Quote from: LaudaM on April 16, 2015, 10:01:27 PM

Quote from: Amph on April 16, 2015, 07:47:07 PM

there are many quote that say otherwise, so no i'm not wrong at all, for a quantum computer brute-forcing a 256 key is like for a normal computer brute-forcing 128 key, it's like dividing by two(the exponent not the number, so is equal to a root square of it), this should be clear, and with that in mind you could deduce easily, that a 128 key for a quantum computer is equal to a 64 key for a modern computer, and a 64 key can be brute-forced with a normal computer(not just one i know, but a very big farm can do it)

just simple logic, you don't need to search for anything to deduce this...

It's actually the other way around. A 128 bit key for a computer is a 64 bit key for a quantum computer. You obviously didn't understand my previous post.
This is theoretical and does not matter at the time. Doing such calculations is currently not possible. Humanity isn't even really near this achievement.

It is better to avoid replying to a thread, than to make bad (due to language or problems understanding) statements.

Quote from: DooMAD on April 16, 2015, 08:59:15 PM

The original one was posted here and probably a few dozen other places as well. I thought the background looked a little dull, so I made my own version.

This doesn't apply to quantum computers. If we could get a quantum computer to operate at the same speeds that we get even mobile processors today we should be able to breach SHA256 with brute force since it is like a 128 bit key for it.

no you are reading that in a wrong way, i said that a 128 key for a quantum is like a 64 for a standard pc, in the sense that a standard pc can break 64 and a QC can break 128

Quote from: shorena on April 16, 2015, 10:14:19 PM

Quote from: Amph on April 16, 2015, 07:47:07 PM

Quote from: LaudaM on April 16, 2015, 06:10:49 PM

Quote from: Amph on April 16, 2015, 01:53:57 PM

now, public key are 128 bit, instead private key are 256, so the first can be brute forced by any quantum computer, and if you have that key you could retrieve the private key, but this only if the targeted public key is send when you spend a transaction

here a link http://bitcoin.stackexchange.com/questions/6062/what-effects-would-a-scalable-quantum-computer-have-on-bitcoin

there are many other confirming this

To summarize: You're wrong. Existing implementations have not shown that they can beat 128bit encryption. They aren't even close. That's the current situation. I'm not saying that in 5 years we won't have better technology. We might operate with 1400 qubits or be stuck at 140. Nobody really knows.

there are many quote that say otherwise, so no i'm not wrong at all, for a quantum computer brute-forcing a 256 key is like for a normal computer brute-forcing 128 key, it's like dividing by two(the exponent not the number, so is equal to a root square of it), this should be clear, and with that in mind you could deduce easily, that a 128 key for a quantum computer is equal to a 64 key for a modern computer, and a 64 key can be brute-forced with a normal computer(not just one i know, but a very big farm can do it)

just simple logic, you don't need to search for anything to deduce this...

well my intention was not say that it could break sha256, but all i want to said, is that it could break 128 key, that's it, there is nothing flawed about my logic