By Jeff Hinson CS691, Summer 2009 Quantum Cryptography By Jeff Hinson CS691, Summer 2009

Brief History Idea born in late 60’s with Stephan Wiesner’s “Conjugate Coding” 1st successful quantum exchange: October 1989 Charles Bennet and Gilles Brassard expand idea to “Quantum Key Distribution Channel” Has been a growing topic, especially in the past decade CS691 Jeff Hinson Summer 2009

Quantum Channels Needed equipment: The idea: Fiber-optic cable photon cannons on each end filters for polarization The idea: Two computers: Alice and Bob Alice polarizes a photon using a filter, sends to Bob Bob receives photon, tries to read using a filter; guesses the polarization CS691 Jeff Hinson Summer 2009

Quantum Channels (cont.) Problem: unrealistic for regular use unreliable, Bob must guess Alice’s polarization normal internet connection still needed to verify accuracy of transmission on quantum channel Photon-reading is slow, especially over large distances (~10kb/s) Advantages: difficult to hack; can tell if someone is eavesdropping on the line... CS691 Jeff Hinson Summer 2009

Quantum Key Distribution Makes quantum channels more realistic The Idea: use a quantum channel to send photons from Alice to Bob Bob tells Alice what he thinks Alice’s polarizations were Alice confirms/denies. Wrong bits are discarded, remaining bits are the new key Key is used to encrypt/decrypt data send over a regular channel CS691 Jeff Hinson Summer 2009

Quantum Key Distribution (cont.) Cons still expensive slow connection over short distances Pros very secure; is difficult to guess the key can tell if someone is eavesdropping: measuring the photos will change their state if Bob gets X number of bits wrong, eavesdropping is assumed; key discarded and a new channel is used to distribute the key CS691 Jeff Hinson Summer 2009

Eavesdropping Intercepting/Resend Beam-splitting traditional approach; easily detectable ideas to read momentum without measuring; study still shows it to be detectable Beam-splitting Photons difficult to send one at a time; if multiple photons are sent, eavesdropper can split beam to read one and pass others on without being detected Is difficult to do, highly unreliable, and chance of detection still exists CS691 Jeff Hinson Summer 2009

In the News... Cambridge team found way to transmit up to 10mb/s over large distance (20km) on lower-cost components Spain plans to release 1st metropolitan quantum cryptography network by 2010 Austrian scientists made successful quantum connection over 90mi distance CS691 Jeff Hinson Summer 2009

Conclusions Quantum channel not likely to be used for regular connections anytime soon Quantum Key Distribution is a good idea, and is very quickly becoming realistic As scientific advancements are made, cost will decrease, and reliability and efficiency will increase It sounds like a lot of fun, and makes for good dinner conversation.... CS691 Jeff Hinson Summer 2009

Questions/Comments?