Quantum Computers

[timo]

@5614:

I do very well understand what you say, I think. I am however afraid that you dont get my point which probably is because I was too lazy to write a good post explaining my point in detail and because you should really take more time than 5 minutes before writing a response (honestly: 5 minutes does not make the impression you really tried to understand).

 

Let´s agree that the message is coded with a random key of the same lenght by an XOR-operation so we have at least some basis to discuss upon.

 

What you are saying is that I just have to check each key and you will have the original message sooner or later. That´s absolutely correct. What you also say is that the problem is to know when you got the right key. That´s in fact the point.

Try to switch message and key. The transmitted message will of course remain the same because K XOR M = M XOR K. Now try each possible message until you get the correct key. I hope we can agree that you are absolutely not able to tell which one of the keys was the original one (because it was random by definition).

 

I hope that clearifies the problem a bit. While I said "you can´t get the message because you don´t know which of the possible keys was used" you said "you can get the key if you know which one of the possible messages was transmitted". Both statement are correct.

[5614]

yeah, agreed!

 

but what im saying is that say this is english language encrypted randomly... by trial and error and a process of elimination you could crack the code.

 

however if this is goble-dee-gook encrypted randomly... you could never decrypt it as you'd never recognise the goble-dee-gook as the original message, whereas if you keep trying loadsa combinations and suddenly you get english sentences you'd recognise it.

 

do you agree that any code is crackable?

 

do you agree that the above is only true if you would recognise the decrypted message when you saw it?

 

^ (thats what i think anyway).

[timo]

yeah' date=' agreed!

 

but what im saying is that say this is english language encrypted randomly... by trial and error and a process of elimination you could crack the code.

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Look back to my examples, especially the part where I said try to exchange code and message. If the message is in english then you only have to check all possible messages with english text in it to get the key. However, I strongly doubt that there´s only one possible english message having a size of say 1000 characters so you can´t get the key.

 

however if this is goble-dee-gook encrypted randomly... you could never decrypt it as you'd never recognise the goble-dee-gook as the original message, whereas if you keep trying loadsa combinations and suddenly you get english sentences you'd recognise it.

Great. I know it´s possible to write an english text with the required length, then. Could have guessed so before.

 

do you agree that any code is crackable?

No, that´s what we are debating about, I think. Of course it´s possible to get the correct key but it´s impossible to know it when you have it.

 

do you agree that the above

 is only true if you would recognise the decrypted message when you saw it? 

Yes.

[5614]

No, that´s what we are debating about, I think. Of course it´s possible to get the correct key but it´s impossible to know it when you have it.

 

ok, good, so all agreed so far.

 

the only thing debateable now is if there is such a thing to know when it has the code... there obviously is no such thing now, however with the advance processing power of a quantum computer it could be possible as it would be able to go through every combination and just keep on going through millions of calculations a second.... or, well, i dont know... it doesnt exist yet!!!