Do you think quantum computers would break Bitcoin's security?

[Hazir]

Quantum computing studies theoretical computation systems (quantum computers) that make direct use of quantum-mechanical phenomena, such as superposition and entanglement, to perform operations on data.
Large-scale quantum computers will be able to solve certain problems much more quickly than any classical computers that use even the best currently known algorithms.
In theory this kind of computing power will be unbelievably powerful and be able to achieve much greater "solving power" which could crack algorithm behind bitcoin (commonly referred as: public key cryptography).

For more information visit: http://en.wikipedia.org/wiki/Quantum_computing

Bitcoin is designed to last for over a 100 years. Obviously we don't have this kind of computers yet.
But we will be, maybe in 10 maybe in 20 years, but definitely sooner that we may think - and then, at that time bitcoin may be world currency...
So do you think quantum computers would break Bitcoin's security?

[zcxvbs]

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

[Furio]

Quantum computing studies theoretical computation systems (quantum computers) that make direct use of quantum-mechanical phenomena, such as superposition and entanglement, to perform operations on data.
Large-scale quantum computers will be able to solve certain problems much more quickly than any classical computers that use even the best currently known algorithms.
In theory this kind of computing power will be unbelievably powerful and be able to achieve much greater "solving power" which could crack algorithm behind bitcoin (commonly referred as: public key cryptography).

For more information visit: http://en.wikipedia.org/wiki/Quantum_computing

Bitcoin is designed to last for over a 100 years. Obviously we don't have this kind of computers yet.
But we will be, maybe in 10 maybe in 20 years, but definitely sooner that we may think - and then, at that time bitcoin may be world currency...
So do you think quantum computers would break Bitcoin's security?

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

[Amph]

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

[randy8777]

technology develops in a very quick fashion. what today can be seen as secure and not possible to crack might be something we laugh at in 2020 or so. it's just a matter of years.

[Lauda]

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.

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.

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.

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.

[Jybrael]

Well it is still theoretical...and until we can actually have a quantum computer built we wouldn't really know and besides I am sure they might able to change encryption before that happens...probably make it stronger and we might get an even longer period of time to wait out until technology develops further.

[shorena]

A quantum computer is not an "insanely powerful computer" it uses completely different algorithms. Some are better at certain jobs, some are worse.

http://en.wikipedia.org/wiki/Post-quantum_cryptography

[InceptionCoin]

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.

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.

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.

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

[Fabrizio89]

It won't affect it, no. Eventually something will break it, not in the next 15 years though I believe.

[fairglu]

But we will be, maybe in 10 maybe in 20 years, but definitely sooner that we may think - and then, at that time bitcoin may be world currency...
So do you think quantum computers would break Bitcoin's security?

It would first need to crack SHA-256

http://miguelmoreno.net/wp-content/uploads/2013/05/fYFBsqp.jpg

The numbers are really giganormous.

2^256 is is about 1e77, or 1 followed by 77 zeroes.

This is a number not too far from that of the number of atoms in the whole observable universe which is 1e80 ...  http://en.wikipedia.org/wiki/Observable_universe#Matter_content_.E2.80.94_number_of_atoms

This is also a billion billion billion times more than then number of atoms in the whole earth (about 1e50).

So any brute-force derived from Moore's Law will be completely unable to break SHA-256, and sheer computing power gains from Quantum computing (if they ever materialize, which they have not yet) will not either, at least until a sizeable portion of the observable universe is not brought to work in it.

Smart insight and unforeseen vulnerabilities could lead to a break tomorrow, or yesterday. But Quantum and Moore's Law? Nope.

[redsn0w]

Yes, I think in the next 10-15 years the technology will grow (that's normal) and maybe the will break the sha 256 bit but first you should remember also the banks use this algo, and I think someone will be interested in the bank (for first) and after all the other things (money related) that are using sha 256 bit.

So at the end I am not worried, if an hypothetical quantum computer will he created, the first target will be the banks.

[DarkHyudrA]

A more powerful computer doesn't mean that it will break any cryptography.
Remeber that better computers means only faster brute force attacks.

[Lauda]

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

I rarely say things without being mostly certain of them being correct (I do make mistakes of course). Most replies to this thread will just be useless, and a different/shorter version of what someone else said (i.e. legit spam).
Anyhow I'm not sure that Grover's algorithm could be extended to brute force SHA256. Isn't it supposed to be some sort of database searching algorithm?

[Amph]

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.

you are wrong it can break 128 key(the power of quantum computer is like a pc that halve the difficulty, and if today pc, tons of them, could break 64, then a quantum can break 128) this is not enough to break sha256(or the private key which is 256 bit) i know, i didn't explain it well, but it is enough to break the pubblic key which is 128 bit

[Lauda]

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.

you are wrong it can break 128 key(the power of quantum computer is like a pc that halve the difficulty, and if today pc, tons of them, could break 64, then a quantum can break 128) this is not enough to break sha256(or the private key which is 256 bit) i know, i didn't explain it well, but it is enough to break the pubblic key which is 128 bit

Your English levels are under those of a 5th grader. Consider taking a course, because you complicate things and usually make no sense.
I never said that SHA256 for a normal computer wasn't SHA128 for a quantum one. You didn't explain it because it can't be explained well i.e. what you said effectively makes no sense. A quantum computer can't beat SHA 256 (i.e. SHA 128). Actually if SHA gets broken the problem will be on a much larger scale where Bitcoin will be irrelevant (unless globally adopted). A lot of things use SHA, for example banks.

What I'm trying to say is: For SHA256, it effectively becomes SHA128 to a Quantum computer. Now the question remains, can a Quantum search for SHA128 faster than a classical computer search through SHA256?
With out current technology and for the near future, we still can't build a real Quantum computer that can even begin to tackle this problem, let alone solve it.
Correction 21-05-2020, for reason reported here. As I said in my reply, I must have unknowingly repeated and paraphrased text that I had previously read and remembered. It was not intentional.

Original of highlighted text:
https://web.archive.org/web/20130720024745/https://bitcointalk.org/index.php?topic=78693.0#msg876353

Archive of unedited post:
https://web.archive.org/web/20150514022942/https://bitcointalk.org/index.php?topic=1026125.0#msg11104992


[original post, with paraphrased text highlighted]

[ticoti]

I think that bitcoin would not be the main problem in the world if quantum computers appear, there are banks,governments and many security systems more fragile for the humankind than bitcoin

[kelsey]

when it can bitcoin's security will be the least of your problems  

[redsn0w]

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 javascript:void(0);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.

you are wrong it can break 128 key(the power of quantum computer is like a pc that halve the difficulty, and if today pc, tons of them, could break 64, then a quantum can break 128) this is not enough to break sha256(or the private key which is 256 bit) i know, i didn't explain it well, but it is enough to break the pubblic key which is 128 bit

Your English levels are under those of a 5th grader. Consider taking a course, because you complicate things and usually make no sense.
I never said that SHA256 for a normal computer wasn't SHA128 for a quantum one. You didn't explain it because it can't be explained well i.e. what you said effectively makes no sense. A quantum computer can't beat SHA 256 (i.e. SHA 128). Actually if SHA gets broken the problem will be on a much larger scale where Bitcoin will be irrelevant (unless globally adopted). A lot of things use SHA, for example banks.

What I'm trying to say is: For SHA256, it effectively becomes SHA128 to a Quantum computer. Now the question remains, can a Quantum search for SHA128 faster than a classical computer search through SHA256?
With out current technology and for the near future, we still can't build a real Quantum computer that can even begin to tackle this problem, let alone solve it.

Nobody know the real answer for that question, but I think the technology of the next 10-15 will not the same of now (this is obvious). I think the quantum computer (if it will be created) can really resolve-crack the sha 128 bit easily but I don't know if it can crack the sha256.

[NeuroticFish]

While hardware changes, software changes too.
Quantum computers may be or may not be what you actually expect.

The only way I see bitcoin to be hacked is that somebody will be able to generate as "vanity" address your address if it has bitcoin on it. With a fast enough computer it may worth it at some point.
However, as I said, while hardware changes, software changes too. Adding some anonymity into bitcoin could fix this quite easily (though everybody will have to move the coins from the old known public wallet if they want safety).

And this is one of the small changes. Even changing algo is an option. Somebody said that such change will need new equipment.
Bad news for the miners: if a quantum computer will be that fast, it will also be faster than the ASICs on hashing. So the ASICs will have to be thrown away anyway.
And if mining goes back to CPU, changing algo is.. just another change in life.