David Kirkpatrick

June 11, 2008

Quantum cryptography

Move over one-time pad, there’s a new kid on the cryptographic block — quantum cryptography. This is one amazing application for the weirdness that is quantum mechanics and quantum effects. And one cool way to transmit secret messages.

Today’s KurzweilAI.net newsletter had a link to a Scientific American story on space-based quantum codes used for cryptography.

Over at Bad Astronomy, Phil Plait wrote about this on Monday. He offers a cool short-version explanation of the quantum mechanics involved, and his comment section has even more detail provided by BABlog readers.

Here’s the KurzweilAI  short:

Space Station Could Beam Secret Quantum Codes by 2014
ScientificAmerican.com, June 9, 2008

University of Vienna researchers hope to send an experiment to the International SpaceStation (ISS) by the middle of the next decade that would pave the way for transcontinental transmission of secret messages encoded using quantum entanglement.


(European Space Agency

In addition to potential use for secure communications, the “Space-QUEST” project would give researchers a chance to test the theory that entanglement should be unlimited in range.

 
Read Original Article>>

 

Here’s an excerpt from the Scientific American link found above at “Read Original Article”:

Researchers hope to send an experiment to the International Space Station (ISS) by the middle of the next decade that would pave the way for transcontinental transmission of secret messages encoded using the mysterious quantum property of entanglement.

When two particles such as photons are born from the same event, they emerge entangled, meaning they can communicate instantaneously no matter how far apart they are. Transmitting entangled pairs of photons reliably is the backbone of so-called quantum key distribution—procedures for converting those pairs into potentially unbreakable codes. Quantum cryptography, as it is known, could appeal to banks, covert government agencies and the military, and was tested in a 2007 Swiss election

Here’s some of Phil Plait’s commentary at Bad Astronomy:

So some European scientists came up with the idea of using the International Space Station (I know! Using ISS for science! Wow!) to test this out. They can create a small setup with a laser which can create entangled photons. The entangled photons are then sent simultaneously to two different ground stations, widely separated on the surface of the Earth, so that both have a copy of the entangled photons. In addition, two quantum keys are created based on the photons; this is essentially a code based on the state of the photons — like winning a bet is based on which way a coin lands. The two keys are different, and one each is sent to the two ground stations. So both stations have a pair of entangled photons (identical to the other station’s) and a different key.

Each key is actually a long chain of 1s and 0s. The two keys are then compared on the ISS to create what’s called a bitwise XOR — for example, if two coins both land heads then the XOR operation yields a 0, but if they land differently (one heads and one tails) then it yields a 1 — it’s just telling you whether they are the same or different. So for each place in the key, the two numbers are compared, and if they’re the same (both 1s or both 0s) then a 0 is written down. If they are different then a 1 is put there. When this is done, you get a third string of 1s and 0s, representing a comparison of the two keys.

Still with me? Yeah, me neither, but we’re almost done. So now the ISS has this long number string which represents whether the keys are alike or different. It then transmits this to one of the two stations on Earth.

So? What does this mean? This means that now the two ground stations can create a code between them based on their keys, a code that is known only to them and no one else. Furthermore, this code cannot be cracked by anyone, anywhere, because it’s based on entangled photons that cannot be known to anyone else! Because of entanglement, they know what the other station has because they can look at their key and figure it out. But no one else can.

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