Quote from: LaudaM on April 16, 2015, 10:34:21 AM

I don't think that we will be facing a problem 'soon'. If quantum computers break ECDSA (The Elliptic Curve Digital Signature Algorithm) which is used for signing transactions, we might be facing a problem. I'm pretty sure that most members here don't know what happens in this scenario. If the algorithm gets broken, anyone with a quantum computer could extract a private key from any public key and take the Bitcoin stored on it.

It does look simple doesn't it? Well it's not like that. The thing is that your public key isn't really made public, but your Bitcoin address is rather a hash of it. What I'm saying is that while a quantum computer could get the private key from a public key, it can't derive the public key from your Bitcoin address.

Quote from: Amph on April 16, 2015, 07:21:05 AM

on sha256 security bit are only 128, and quantum computer can break this(i can't find the article), if today pc can break 64 quantum computer can break at least the double of that
so bitcoin will need an hard fork in the future to survive

Stop talking nonsense. Quantum computers can't break SHA256 (used for hashing) without brute forcing it unless a flaw in it has been found. There is no article to link. I'm not saying that someone won't find a way to attack it in the future though.

Quote from: Furio on April 16, 2015, 06:44:28 AM

Bitcoin is SHA256, SHA2 hasn't even been broken yet, once 256 will be broken, the bitcoin algo can change to SHA512 for another 40/50 years

This is wrong too. While it looks 'simple' it definitely is not. You do realize that changing the hashing algorithm means that all the current mining equipment would become worthless?
If SHA256 gets broken that would cause huge problems. Changing the signing algorithm is much easier than the hashing one, if you look at the big picture.

Quote from: zcxvbs on April 16, 2015, 06:43:50 AM

Technology are developing, everything is possible in the future, maybe Bitcoin will be obsolete in next 100 year, even before all Bicoin were mined.

This is why a better way of upgrading is needed. Hard forks are complicated and there will always be people who think that they know better than the people who are actually working on the software itself.

Note: Finally a decent topic has been made after a while.

You are right. To summarise your answer:
1. quantum computers(qc) will be able to get you privkey from public key. But your address isn't your public key its hash160(pubkey). Do we need to change something with addresses after qc? Yes. When you spend money you reveal your pubkey(so every one could hash160 it compare with addr in the transactions and check that you have privkey). So 1) you should never send coins to the address from which you already sent something(its good advice to use new addr each time), 2) when qc will come bitcoin probably will make hardfork and will change sign algo.
2. About mining. There is Grover's algorithm which allow to speed up brute forcing of the sha256(this is what all miners do) but its not a inverse function of sha256. So we just get next mining revolution like cpu->gpu, gpu->asic and so on