Quantum CryptographyBrief HistoryQuantum ChannelsQuantum Channels (cont.)Quantum Key DistributionQuantum Key Distribution (cont.)EavesdroppingIn the News...ConclusionsQuestions/Comments?Quantum CryptographyQuantum CryptographyBy Jeff HinsonCS691, Summer 2009Brief HistoryBrief HistoryIdea born in late 60’s with Stephan Wiesner’s “Conjugate Coding”1st successful quantum exchange: October 1989Charles Bennet and Gilles Brassard expand idea to “Quantum Key Distribution Channel”Has been a growing topic, especially in the past decadeCS691 Jeff Hinson Summer 2009Quantum ChannelsQuantum ChannelsNeeded equipment:◦Fiber-optic cable◦photon cannons on each end◦filters for polarizationThe 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 polarizationCS691 Jeff Hinson Summer 2009Quantum Channels (cont.)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 2009Quantum Key DistributionQuantum Key DistributionMakes quantum channels more realisticThe 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 channelCS691 Jeff Hinson Summer 2009Quantum Key Distribution Quantum Key Distribution (cont.)(cont.)Cons◦still expensive◦slow connection over short distancesPros◦very secure; is difficult to guess the key◦can tell if someone is eavesdropping:measuring the photos will change their stateif Bob gets X number of bits wrong, eavesdropping is assumed; key discarded and a new channel is used to distribute the keyCS691 Jeff Hinson Summer 2009EavesdroppingEavesdroppingIntercepting/Resend◦traditional approach; easily detectable◦ideas to read momentum without measuring; study still shows it to be detectableBeam-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 existsCS691 Jeff Hinson Summer 2009In the News...In the News...Cambridge team found way to transmit up to 10mb/s over large distance (20km) on lower-cost componentsSpain plans to release 1st metropolitan quantum cryptography network by 2010Austrian scientists made successful quantum connection over 90mi distanceCS691 Jeff Hinson Summer 2009ConclusionsConclusionsQuantum channel not likely to be used for regular connections anytime soonQuantum Key Distribution is a good idea, and is very quickly becoming realisticAs scientific advancements are made, cost will decrease, and reliability and efficiency will increaseIt sounds like a lot of fun, and makes for good dinner conversation....CS691 Jeff Hinson Summer
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