Thoughts on quantum encryption

[kleptophobiac]

In order to generate the data stream, emitter and detector must be able to write and read the quantum states of photons.

Part of the professed security to the system is the inability to tap the system without alerting the sender and recipient. Why could a hacker use a receiver/transmitter pair and digitize the incoming photons, and record the data, and retransmit the photons that the real recipient expects? This would require the installation of the device on the fiber line, but that shouldn't be too terrible to do for anyone who is truly interested in eavesdropping. Fiber lines run unprotected for miles, and if there's no live traffic on the line when the break is introduced, nobody will notice.

Of course, the bits must then be decrypted to be useful, but I'm just pointing out that part of the system's advertised security could be destroyed using the same technology.

 

[Jennifer]

It wouldn't work. Because of the nature of optical fibre it's carrying more than one data stream, many many more infact. The trick would be to filter out the data that wasn't relevant. Or you'd spend the next 5000 years decrypting things you wouldn't need.

 

[BlindedByScience]

Fiber lines run unprotected for miles, and if there's no live traffic on the line when the break is introduced, nobody will notice.

Not true. Secure fiber optical cables have tap / intrusion detection that operates on a layer independant of the network traffic. Pretty basic physics involved and while it's not completely foolproof, it's damn good....

Also, keep in mind that for really secure systems, they are always kept busy. I've had friends that were in "the business" and they said they send news, music, text, anything - just total crap data - fully encrypted - all the time. The sensitive stuff in in there, too, but if you are just tapping into the hose, you've still got the "needle in the haystack" issue to deal with.

FWIW - B.B.S.

 

[MartinX]

In order to generate the data stream, emitter and detector must be able to write and read the quantum states of photons.

Part of the professed security to the system is the inability to tap the system without alerting the sender and recipient. Why could a hacker use a receiver/transmitter pair and digitize the incoming photons, and record the data, and retransmit the photons that the real recipient expects? This would require the installation of the device on the fiber line, but that shouldn't be too terrible to do for anyone who is truly interested in eavesdropping. Fiber lines run unprotected for miles, and if there's no live traffic on the line when the break is introduced, nobody will notice.

Of course, the bits must then be decrypted to be useful, but I'm just pointing out that part of the system's advertised security could be destroyed using the same technology.

I was under the impression that the point of quantum encryption was that the frequency/polarity of the physical photons was used as sort of part of the checksum/hash rather than just the message contents which previous systems use for validation, and because of the Heisenberg Uncertainty principle thing it was basically "impossible" to recreate/replicate that component undetectably after doing anything with the transmission.

I use the term "impossible" advisedly, because obviously nothing is over time.

Also, your mechanism assumes a single path/sequence transmission, which is by no means certain, to get a decryptable message you'd presumably have to capture masses of traffic and the amount of time involved in processing/decrypting it may well render any useful data obsolete.
It may well be doable, but the work effort may render it impotent (which is sort of the point of encryption in the first place).

I'm not a cryptographer, physicist or mathmatician though, so that's just my limited understanding of it, and may be totally wrong.

*Edit* is a an encrypted stream of photons even distinguishable from generic optical noise/traffic? I mean, assuming you captured a bunch of traffic invisibly, would you even be able to identify/separate the encrypted stream from the regular traffic easily.

*Edit2* Hey...waitaminute, this isn't "Networking and Security"...

 

[jared2027]

Part of the professed security to the system is the inability to tap the system without alerting the sender and recipient. Why could a hacker use a receiver/transmitter pair and digitize the incoming photons, and record the data, and retransmit the photons that the real recipient expects? This would require the installation of the device on the fiber line, but that shouldn't be too terrible to do for anyone who is truly interested in eavesdropping. Fiber lines run unprotected for miles, and if there's no live traffic on the line when the break is introduced, nobody will notice.

The reason the man-the-middle attack does not work is that he has no way of knowing if the bits he detected were in the correct position or not. He also cannot "forward" the photons in the same state that they were sent since any attempt to "look" at them causes interference. Even the intended receiver does not know which bits he got correct until he syncs with the sender. After he has established what bits are to be used as a key, the data is encrypted and sent over classic encryption channels.

Quantum encryption is simply used as a method to generate and distribute random bits to be used as a key. Think of it as a secure way of distributing one-time pads. Sure you can generate a lot of one-time pads and distribute them on a cd/dvd, but you must have a high level of assurance it will not get intercepted.

 

[kleptophobiac]

If the states of these photons are part of the key, and the key must be transmitted to another source, that means there is forced creation of photons in these states and the reception of the state data.

Why couldn't somebody interrupt the stream completely, and just retransmit whatever comes back. The uncertainty principle states that you cannot know momentum and position of any single particle at a given time, and shouldn't preclude retransmission of identical particles.

On a theoretical level, I don't see why interception of the key bits wouldn't be possible. Of course you'd have to dig up the fiber, and then actually have this theoretical device, and then install this theoretical device, then hope nobody noticed the line interruption (including the automatic monitors) -- in other words, it's not going to happen. Even if it did happen, the point has been made that there's a ton of extra data on these networks that serves no purpose other than to increase the size of the haystack.

I just don't understand why I can't read the bits, store the bits in RAM, and retransmit the bits using equipment similar to that which created them in the first place. If the state can be maniuplated or "modulated" to carry data, then it is possible anywhere along the data stream. It could probably be detected, maybe because of the transmission delay introduced by the extra "hop", but in terms of actual data received, I don't see why it wouldn't be possible to steal the key.

 

[jared2027]

If the states of these photons are part of the key, and the key must be transmitted to another source, that means there is forced creation of photons in these states and the reception of the state data.

Why couldn't somebody interrupt the stream completely, and just retransmit whatever comes back. The uncertainty principle states that you cannot know momentum and position of any single particle at a given time, and shouldn't preclude retransmission of identical particles.

On a theoretical level, I don't see why interception of the key bits wouldn't be possible. Of course you'd have to dig up the fiber, and then actually have this theoretical device, and then install this theoretical device, then hope nobody noticed the line interruption (including the automatic monitors) -- in other words, it's not going to happen. Even if it did happen, the point has been made that there's a ton of extra data on these networks that serves no purpose other than to increase the size of the haystack.

I just don't understand why I can't read the bits, store the bits in RAM, and retransmit the bits using equipment similar to that which created them in the first place. If the state can be maniuplated or "modulated" to carry data, then it is possible anywhere along the data stream. It could probably be detected, maybe because of the transmission delay introduced by the extra "hop", but in terms of actual data received, I don't see why it wouldn't be possible to steal the key.

I suggest reading this article which does a good job of describing how it works. The "Receiving Is the Key" & "Detecting Interlopers" sections are especially helpful.

 

[kleptophobiac]

Good link, thanks!