Quantum cryptography
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Quantum Cryptography. By Jeff Hinson CS691, Summer 2009. Brief History. Idea born in late 60’s with Stephan Wiesner’s “Conjugate Coding” 1 st successful quantum exchange: October 1989 Charles Bennet and Gilles Brassard expand idea to “Quantum Key Distribution Channel”

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Quantum Cryptography

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Quantum cryptography

Quantum Cryptography

By Jeff Hinson

CS691, Summer 2009


Brief history

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

CS691Jeff HinsonSummer 2009


Quantum channels

Quantum Channels

  • Needed equipment:

    • 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

CS691Jeff HinsonSummer 2009


Quantum 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...

CS691Jeff HinsonSummer 2009


Quantum key distribution

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

CS691Jeff HinsonSummer 2009


Quantum key distribution cont

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

CS691Jeff HinsonSummer 2009


Eavesdropping

Eavesdropping

  • Intercepting/Resend

    • 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

CS691Jeff HinsonSummer 2009


In the news

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

CS691Jeff HinsonSummer 2009


Conclusions

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....

CS691Jeff HinsonSummer 2009


Questions comments

Questions/Comments?


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