Quantum encryption

Factual Questions
1

I do not understand this article: http://www.msnbc.com/news/835606.asp
It says it talks about data encryption but actually talks about data transmission.

The way I understand things: Encryption is the process by which, using a process or program which is assumed to be in the public domain and a key (data), you transform data into another data which does not readily reveal the original information. To reveal the original information you use a decyphering process and a decyphering key. All this has zero to do with data transmission.

Data transmission through a data channel, whether encrypted or not, is a totally different issue which deals with getting the information reliably from point A to B. Issues here are noise which distorts the data and whether the channel can be tapped by others who would then have access to the info.

The article in question seems to say data transmitted through a quantum channel would be safe because if a third party accesses the channel then the information is destroyed. Fine, that may be a secure transmission channel but it is not encryption.

Encryption is often used before transmission in channels which may not be secure but encryption and transmission remain totaly separate issues and that is why I do not understand the article. Can someone explain the article? Or is it just the writing of a reporter who doesn’t understand the topic?

2

We just had a lecture on quantum encryption in physics the other day. As best as I can tell, you’re right. The way quantum encryption works is you use quantum transmission to transmit the encryption key. The “No-Cloning Theorem” basically says you can make a signal which can only be read once, so if the person you’re transmitting to isn’t reading it, you know someone else is. After you have securely transmitted the key, you use whatever means you feel like to transmit your regular encrypted message. It doesn’t make the data themselves more secure, only the key.

3

I think you are trying to make a distinction that in the quantum world makes no sense. Any message has to be encoded to be transmitted. Ascii is a code. A public code. A one time pad is generally considered as an encryption device even though it is invariably used for transmission. Think of quantum encryption as a one-time pad consisting of entangled particles. You use one to encrypt and send the other to decrypt. A fraction of the bits are not used to encrypt but tested to ensure that no one has eavesdropped. But that is a detail. But you cannot use it to encrypt data for your own computer since the entanglement will end eventually. Of course you could still use the random sequence of bits to construct an actual one-time pad, so quantum encryption is still possible.