Most likely, a time travel path would be along a line of freefall (geodesic). ie. Imagine if you could fall through the ground, wobbling back and forth from one side of the planet to the other.
For any given initial velocity, there would only be certain periodic times when you *wouldn't* end up inside the planet. And the position on the planet where you come out would also be problematic. If you're not satisfied with those precise times and places, then you can adjust your velocity a tad, to get another set of options.
If you're in orbit then you have much less to worry about.
I'm not talking about a statistical attack. I'm talking about something very basic and fundamental. What happens if you turn A=====B into A=====C-C=====B?
I am saying - If the intended receiver can get any useful data EVER, then why can't an interceptor do exactly the same thing? If the sender can EVER get any data across the line, then why can't an interceptor do exactly the same?
Are you implying that the receiver has some unique ability that nobody else in the world can have? Is only this one specific receiver out of all the people in the world able to make an photon measuring apparatus? That is absurd.
An attacker simply has to act like the receiver to get the data, then act like the sender and resend the data.
He only has to measure once. The receiver never gets to see the photons that the original sender sent.
The attacker does not need to duplicate the photons (impossible!). All he needs to do is to send the data with exactly the same *method* as the original sender used.
As for shared secrets, MitM can intercept so that the sender and receiver each share a different secret with the MitM, and the MitM works to translate from one secret to the other. The sender and receiver may *think* they share a secret with each other, but they don't.
The wikipedia article fails to mention this, since it assumes that the man in the middle wishes to keep the secret intact. But he does not have to wish so.
As for using radio for the conventional channel, it still requires some sort of shared agreement - Which frequency do you operate on? And this is just an example of something that tries to make the MitM difficult. A very determined attacker can rig up something to get past this - for example, just put an interceptor into one party's radio.
Listen, if the intended receiver is able to pick up the signal, then a man in the middle can, too!
QC relies on two communications pathways - one conventional to say "keep/don't keep this bit", and the other uses quantum effects so that the bits can only be read once.
If you completely capture both communication lines, then you can impersonate the receiver, and then duplicate the signal and impersonate the sender.
I'm not talking about observing the bits that go down the line. I'm talking about impersonating both sides to each other. That is a man in the middle attack.
One way you can make MitM harder is to have many many communications pathways. For example, imagine if your protocol involved sending 20 streams that must all be XORed together to get the cleartext. An attacker must capture all the pathways to be successful.
The other way to make MitM harder is to have a big enough shared secret. You could have secret passwords, or even a secret protocol would work too. If the MitM can't guess the shared secret, then impersonation will fail.
Some people have proposed a way of quantum key generation via entangled particles. But remember that getting this shared secret to each other is also subject to MitM attacks. Someone can yoink those entangled particles, and throw in new ones. Then when you communicate later on, he just decrypts with one key and then re-encrypts with the other.
You can make it very impractical for an attacker to succeed, even so hard that no known human would have the resources to pull it off. But who knows - you still have no absolute guarantee.
The person you're talking to can always be an impersonator. It can be really improbable, but there is always some possibility. I'm not saying you should be paranoid, but just that every communication involves a degree of trust. Quantum magic won't make that required trust go away.
The 'man in the middle' attack always has a way to work. Always always always always. You can set up your encryption so that he would have to capture multiple channels, but there is always a way to do a 'man in the middle' attack.
"The amount of electricity" - would that be amps, volts, or watts?
"Less than the amount required to power a cell phone" - really now, and even if I scale up the process by a factor of 10, it will still take the same amount? AMAZING!
Because kids are starting to learn that Computer Science is not about computers.
Oh sure, I love computers and everything, but I realized early on in University that Computer Science is not about the parts I like. All the fun bits about computers show up in other careers, like real science.
That's exactly what conservative wackos say when a billionaire decides to stand up for "family values" and such.
If we accept that the likes of Bill Gates may use their influence in politics, then we cannot honestly use the abuse-of-power rhetoric against the conservative rich guys.
If we are to be fair, then there are two exclusive modes we can pick on this specific issue: 1) Freedom, or 2) Regulation.
Critics say that political freedom circumvents democracy by weighing votes with wealth, and brings us closer to a plutocracy.
There are problems with regulation, too.
But far more dangerous than either choice is if we decide to regulate political actions based on their content.
Historical experience tells us that this is how democracies turn into dictatorships. It is probably a symptom of bad things to come, rather than a cause.
You may recall that the Nazi party was elected partly because the average Joe was afraid of having his job stolen (out-sourced) by the evil rich people. [In their case, it was percieved that rich = Jew].
In light of that, possibly the best thing we can do is to have people stop feeling strongly about the rich. No jealousy, no hatred.
When your entire home directory is deleted - all your work, all your bookmarks, all your records, all your porn - does it really MATTER that the rest of your system is still intact?
This message brought to you by the Society For Capability-Based Security (SFCBS).
Just the other day, I accidentally handed my student card to a cashier at a gas station. She just rung it up without looking at it, and only noticed when it beeped an error message.
Slashdot Mirror
Most likely, a time travel path would be along a line of freefall (geodesic). ie. Imagine if you could fall through the ground, wobbling back and forth from one side of the planet to the other.
For any given initial velocity, there would only be certain periodic times when you *wouldn't* end up inside the planet. And the position on the planet where you come out would also be problematic. If you're not satisfied with those precise times and places, then you can adjust your velocity a tad, to get another set of options.
If you're in orbit then you have much less to worry about.
I'm not in a sheep's body though. (I think)
No. They're pretty much equal on this respect unfortunately...
Because it's new? Are you a luddite?
It's the same every time.
Duh.
If public channels are so guaranteed as you seem to think, then there is a way around MitM even without any quantum stuff.
I'm not talking about a statistical attack. I'm talking about something very basic and fundamental. What happens if you turn A=====B into A=====C-C=====B?
l e_attack#Impossibility_of_fixing_this_problem
I am saying - If the intended receiver can get any useful data EVER, then why can't an interceptor do exactly the same thing? If the sender can EVER get any data across the line, then why can't an interceptor do exactly the same?
Are you implying that the receiver has some unique ability that nobody else in the world can have? Is only this one specific receiver out of all the people in the world able to make an photon measuring apparatus? That is absurd.
An attacker simply has to act like the receiver to get the data, then act like the sender and resend the data.
He only has to measure once. The receiver never gets to see the photons that the original sender sent.
The attacker does not need to duplicate the photons (impossible!). All he needs to do is to send the data with exactly the same *method* as the original sender used.
As for shared secrets, MitM can intercept so that the sender and receiver each share a different secret with the MitM, and the MitM works to translate from one secret to the other. The sender and receiver may *think* they share a secret with each other, but they don't.
The wikipedia article fails to mention this, since it assumes that the man in the middle wishes to keep the secret intact. But he does not have to wish so.
As for using radio for the conventional channel, it still requires some sort of shared agreement - Which frequency do you operate on? And this is just an example of something that tries to make the MitM difficult. A very determined attacker can rig up something to get past this - for example, just put an interceptor into one party's radio.
At least someone else agrees with me:
http://en.wikipedia.org/wiki/Talk:Man_in_the_midd
Listen, if the intended receiver is able to pick up the signal, then a man in the middle can, too!
QC relies on two communications pathways - one conventional to say "keep/don't keep this bit", and the other uses quantum effects so that the bits can only be read once.
If you completely capture both communication lines, then you can impersonate the receiver, and then duplicate the signal and impersonate the sender.
I'm not talking about observing the bits that go down the line. I'm talking about impersonating both sides to each other. That is a man in the middle attack.
One way you can make MitM harder is to have many many communications pathways. For example, imagine if your protocol involved sending 20 streams that must all be XORed together to get the cleartext. An attacker must capture all the pathways to be successful.
The other way to make MitM harder is to have a big enough shared secret. You could have secret passwords, or even a secret protocol would work too. If the MitM can't guess the shared secret, then impersonation will fail.
Some people have proposed a way of quantum key generation via entangled particles. But remember that getting this shared secret to each other is also subject to MitM attacks. Someone can yoink those entangled particles, and throw in new ones. Then when you communicate later on, he just decrypts with one key and then re-encrypts with the other.
You can make it very impractical for an attacker to succeed, even so hard that no known human would have the resources to pull it off. But who knows - you still have no absolute guarantee.
The person you're talking to can always be an impersonator. It can be really improbable, but there is always some possibility. I'm not saying you should be paranoid, but just that every communication involves a degree of trust. Quantum magic won't make that required trust go away.
The 'man in the middle' attack always has a way to work. Always always always always. You can set up your encryption so that he would have to capture multiple channels, but there is always a way to do a 'man in the middle' attack.
"The amount of electricity" - would that be amps, volts, or watts?
"Less than the amount required to power a cell phone" - really now, and even if I scale up the process by a factor of 10, it will still take the same amount? AMAZING!
Because kids are starting to learn that Computer Science is not about computers.
Oh sure, I love computers and everything, but I realized early on in University that Computer Science is not about the parts I like. All the fun bits about computers show up in other careers, like real science.
The president's response at the time, to either style of report: "Oh, it's just some crazy named Bin Laden. As if terrorists could attack the USA."
Have you already forgotten the mindset of the US government before the tower-plane collisions?
That's exactly what conservative wackos say when a billionaire decides to stand up for "family values" and such.
If we accept that the likes of Bill Gates may use their influence in politics, then we cannot honestly use the abuse-of-power rhetoric against the conservative rich guys.
If we are to be fair, then there are two exclusive modes we can pick on this specific issue: 1) Freedom, or 2) Regulation.
Critics say that political freedom circumvents democracy by weighing votes with wealth, and brings us closer to a plutocracy.
There are problems with regulation, too.
But far more dangerous than either choice is if we decide to regulate political actions based on their content.
Historical experience tells us that this is how democracies turn into dictatorships. It is probably a symptom of bad things to come, rather than a cause.
You may recall that the Nazi party was elected partly because the average Joe was afraid of having his job stolen (out-sourced) by the evil rich people. [In their case, it was percieved that rich = Jew].
In light of that, possibly the best thing we can do is to have people stop feeling strongly about the rich. No jealousy, no hatred.
I thought we were supposed to be against companies lobbying the government to have their way? Then this is good!
But I support this kind of legislation. Releasing secret/private information is the only thing which might be called information theft.
(But once it's out in the open, how can you blame someone for obtaining it?)
When your entire home directory is deleted - all your work, all your bookmarks, all your records, all your porn - does it really MATTER that the rest of your system is still intact?
This message brought to you by the Society For Capability-Based Security (SFCBS).
http://slashdot.org/comments.pl?sid=108858&cid=927 4336
There was a slashdot story a while back about this. A guy from JP was answering questions.
For large values of 2.
They're planning to use such airships to launch ships into space, by slowly achieving orbital speed!
We still have the third dimension to exploit.
Tell us next time.
Just the other day, I accidentally handed my student card to a cashier at a gas station. She just rung it up without looking at it, and only noticed when it beeped an error message.
Do it now!
Do it hard!
Let's just ignore the chemical costs of making solar collectors.
They say they're getting 35 MeV electrons. This isn't enough to help out in modern high-energy particle experiments, but still could be useful. Maybe.