At the time being, you are right. But you are wrong if you say that "quantum crypto only works over single lengths of fibre"... There exist proposals for quantum repeaters (see here), and it has been shown that the very techniques used for the repeaters can be used for cryptographic tasks (see here).
For practical quantum crypto systems,
which you can build now, you are right.
OTOH, there exist (theoretical) scemes which
allow for secure
transmission of quantum information over long
distances, using quantum repeaters.
Going to long distance means (in this context),
that the required resources increase only
polynomially with the distance (opposed to an
exponential increase if you do not use a quantum
repeater).
Theoretical means, that there is no experimental
implementation of a quantum repeater yet.
Nevertheless, it would be much easier to build it
than, say, a fault tolerant quantum computer.
Using these techniques, it is possible to build
secure switchable user-to-user channels, which
are secure even if all repeater stations or
switches are under the control of an allmighty
eavesdropper (Eve). As always, Eve can prevent you
from communicating, but if you can communicate,
you can be sure to communicate privatly.
If quantum cryptography was used for
direct communication, you would be right.
But, quantum cryptography should better
be (and often is) called quantum key
distribution. This means, using quantum
crypto, you do not distirbute messages, but keys
only, which (a) do not contain any usable
information, and (b) after having verified that
noone has listened in, are used for classical
one time pad cryptography.
DNA Computers are still classical computers. This means, while they may considerably speed up certain problems, the speed up is always a factor. Even though this factor may be pretty high, it will not really help you if, for example, you want to break RSA-like cryptography: I add some (~100) bits to the length my the crypto-key, and again, you won't be able to break my crypto.
So, if you want for example to factorize large nubers N using a DNA computer, you will have to prepare about sqrt(N) DNA pairs (*). If N is something like 10^200, you are in seriouse trouble! Like, the number of atoms in our universe is less than 10^90... At least, as long as no efficient classical algorithm for factorization has been found.
A qc, on the other hand, would "only" require 200^a qubits, where a is some (not too large) constant > 1.
Note that the situation gets even worse for the DNA computer, if N is of the order of 10^400.
(*) I am not really sure about the square root; there might be some other exponent than N^0.5, but this does not really change the argument...
This actually appears to be the first non-compliant usage of RFC 1149. RFC 1149 specifically indicates that "A band of duct tape is used to secure the datagram's edges."
Nope, you are wrong: the duct tape is only a informal suggestion. Otherwise the statement would be: "A band of duct tape MUST BE used to secure the datagram's edges"
Apart from the fact that this work is actually good work from a principal point of view, it appears to be actually useful. In order to explain why it is is useful, there are more than just a few words needed:
Quantum Cryptogrpaphy, or maybe better Quantum Key Distribution (QKD), is already much more advanced than many people think: there are already groups working on devices that might become really small and cheap in a few years from now.
These devices allow their users to establish a secure key, which might be used as a one-time pad. Secure means in this context, that any eavesdropping strategy allowed by the laws of physics can be detected, and, to some extend, corrected. The latter means that even tough an eavesdropper might have gained partial information on the key, Alice and Bob can amplify the security of that key by (essentially) discarding some of the key bits. This method also helps against the "noise-introduced-by-the-channel-cannot-be-disting uished-from-an-eavesdropper" - issue.
However, all those devices for practical QKD have two problems: Absorbtion and decoherence. Both scale exponentially with the length of the quantum channel used. This is the reason why with current technology it is difficult to go to distances between Alice and Bob which are larger than, say, 100 km.
In order to help against these difficulties (which prevent you from going to large distances in QKD), there are two solutions known (at least, to me): the first is of rather theoretical use: Quantum communication can be thought of as a (rather trivial) special case or quantum computation, and for quantum computation there are codes known (so-called concatenated codes) which allow you to to continue your quantum calculation with polynomial cost. This solution, while elegant from a theoretical point of view, has the disadvantage, that quantum communication becomes techically as difficult as fault-tolerant quantum computation.
The second is the so-called quantum repeater (see http://xxx.uni-augsburg.de/abs/quant-ph/9808065 and the references there in). The quantum repeater is based on entanglement purification and entanglement swapping. Now, the entanglement purification part has been thought to be the more difficult one, as it requires the so-called CNOT gate, which is really difficult to implement for qubits carried by photons. And exactly this part has (at least in theory) been solved by the Zeilinger-group.
What does this mean? Well, it means that quantum communication scaleable to large distances (with ploynomial overhead) might become available in the not-so-far future. At least one of the obstacles on the way to this goal semms to have vanished.
Slashdot Mirror
At the time being, you are right. But you are wrong if you say that "quantum crypto only works over single lengths of fibre"... There exist proposals for quantum repeaters (see here), and it has been shown that the very techniques used for the repeaters can be used for cryptographic tasks (see here).
Going to long distance means (in this context), that the required resources increase only polynomially with the distance (opposed to an exponential increase if you do not use a quantum repeater).
Theoretical means, that there is no experimental implementation of a quantum repeater yet. Nevertheless, it would be much easier to build it than, say, a fault tolerant quantum computer.
Using these techniques, it is possible to build secure switchable user-to-user channels, which are secure even if all repeater stations or switches are under the control of an allmighty eavesdropper (Eve). As always, Eve can prevent you from communicating, but if you can communicate, you can be sure to communicate privatly.
For more details, see e. g. quant-ph/0111066.
IAmHansemann
Hans.
DNA Computers are still classical computers. This means, while they may considerably speed up certain problems, the speed up is always a factor. Even though this factor may be pretty high, it will not really help you if, for example, you want to break RSA-like cryptography: I add some (~100) bits to the length my the crypto-key, and again, you won't be able to break my crypto.
So, if you want for example to factorize large nubers N using a DNA computer, you will have to prepare about sqrt(N) DNA pairs (*). If N is something like 10^200, you are in seriouse trouble! Like, the number of atoms in our universe is less than 10^90... At least, as long as no efficient classical algorithm for factorization has been found.
A qc, on the other hand, would "only" require 200^a qubits, where a is some (not too large) constant > 1.
Note that the situation gets even worse for the DNA computer, if N is of the order of 10^400.
(*) I am not really sure about the square root; there might be some other exponent than N^0.5, but this does not really change the argument...
Nope, you are wrong: the duct tape is only a informal suggestion. Otherwise the statement would be: "A band of duct tape MUST BE used to secure the datagram's edges"
SCNR :-)
Quantum Cryptogrpaphy, or maybe better Quantum Key Distribution (QKD), is already much more advanced than many people think: there are already groups working on devices that might become really small and cheap in a few years from now.
These devices allow their users to establish a secure key, which might be used as a one-time pad. Secure means in this context, that any eavesdropping strategy allowed by the laws of physics can be detected, and, to some extend, corrected. The latter means that even tough an eavesdropper might have gained partial information on the key, Alice and Bob can amplify the security of that key by (essentially) discarding some of the key bits. This method also helps against the "noise-introduced-by-the-channel-cannot-be-disting uished-from-an-eavesdropper" - issue.
However, all those devices for practical QKD have two problems: Absorbtion and decoherence. Both scale exponentially with the length of the quantum channel used. This is the reason why with current technology it is difficult to go to distances between Alice and Bob which are larger than, say, 100 km.
In order to help against these difficulties (which prevent you from going to large distances in QKD), there are two solutions known (at least, to me): the first is of rather theoretical use: Quantum communication can be thought of as a (rather trivial) special case or quantum computation, and for quantum computation there are codes known (so-called concatenated codes) which allow you to to continue your quantum calculation with polynomial cost. This solution, while elegant from a theoretical point of view, has the disadvantage, that quantum communication becomes techically as difficult as fault-tolerant quantum computation.
The second is the so-called quantum repeater (see http://xxx.uni-augsburg.de/abs/quant-ph/9808065 and the references there in). The quantum repeater is based on entanglement purification and entanglement swapping. Now, the entanglement purification part has been thought to be the more difficult one, as it requires the so-called CNOT gate, which is really difficult to implement for qubits carried by photons. And exactly this part has (at least in theory) been solved by the Zeilinger-group.
What does this mean? Well, it means that quantum communication scaleable to large distances (with ploynomial overhead) might become available in the not-so-far future. At least one of the obstacles on the way to this goal semms to have vanished.