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Quantum Quantum CryptographyCryptography

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OverviewOverview

Classical CryptographyClassical Cryptography

Quantum Random Number GenerationQuantum Random Number Generation

Quantum CryptographyQuantum Cryptography Using EntanglementUsing Entanglement Using UncertaintyUsing Uncertainty

DevicesDevices Single-Photon EmitterSingle-Photon Emitter Single-Photon DetectorSingle-Photon Detector

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Classical CryptographyClassical Cryptography

Computational securityComputational security Practical; widely usedPractical; widely used Examples: AES, DES, RC-4, RSA, DH…Examples: AES, DES, RC-4, RSA, DH…

Unconditional securityUnconditional security Breaking is impossibleBreaking is impossible Not practical for most applicationsNot practical for most applications Example: One-time padExample: One-time pad Problem: Key DistributionProblem: Key Distribution

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Insecure communication channelInsecure communication channel

One-time padOne-time pad

0000 1111 0000 1111…0000 1111 0000 1111…Plaintext:Plaintext:

0110 0010 0110 1110…0110 0010 0110 1110…RandomRandom Key: Key:

0110 1101 0110 0001…0110 1101 0110 0001…Ciphertext:Ciphertext:

AliceAlice EncryptioEncryptionn

DecryptioDecryptionn

BobBob

EveEve

KeyKey KeyKey??

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Q. Random Number Q. Random Number GeneratorGenerator

TrueTrue Random Numbers are critical! Random Numbers are critical!Quantum processes are fundamentally randomQuantum processes are fundamentally random

Semi-transparent mirrorSemi-transparent mirrorPhoton sourcePhoton source

11

00

Single-photon detectorSingle-photon detector

Single-photon detectorSingle-photon detector

~50%~50%

~50%~50%2”2”

idQuantique - QuantisidQuantique - Quantis

UnbiasingUnbiasing0100111011…0100111011…

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Quantum CryptographyQuantum Cryptography

Quantum Key DistributionQuantum Key Distribution

Uses laws of quantum mechanicsUses laws of quantum mechanics

Provides unconditional securityProvides unconditional security

One of two fundamentalsOne of two fundamentals UncertaintyUncertainty EntanglementEntanglement

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Using EntanglementUsing Entanglement

Create pairs of entangled photonsCreate pairs of entangled photons

Transmit them to Alice and BobTransmit them to Alice and Bob

Alice and Bob get ‘complementary’ Alice and Bob get ‘complementary’ photonsphotons

Difficult to keep states entangled for Difficult to keep states entangled for long time/distanceslong time/distances

No commercial application yetNo commercial application yet

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Using UncertaintyUsing Uncertainty

Measuring a quantum system Measuring a quantum system disturbs itdisturbs it Alice sends individual quantaAlice sends individual quanta If Eve makes measurements, Bob can’t; If Eve makes measurements, Bob can’t;

that’s tamper-evidentthat’s tamper-evident Eve can’t reproduce the originalEve can’t reproduce the original Neither Eve nor Bob can ever detect the Neither Eve nor Bob can ever detect the

entire stateentire state

Devices by idQuantique and MagiQDevices by idQuantique and MagiQ

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Using Uncertainty – Using Uncertainty – PrinciplesPrinciples

Practical approach uses photonsPractical approach uses photons Photons can be transmitted over long Photons can be transmitted over long

distancesdistances Photons exhibit the required quantum Photons exhibit the required quantum

mechanical propertiesmechanical properties

Quantum properties exploitedQuantum properties exploited Photons can not be divided or duplicatedPhotons can not be divided or duplicated Single measurement is not sufficient to Single measurement is not sufficient to

describe state fullydescribe state fully

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Polarized Photons and Polarized Photons and FiltersFilters

Source: id Quantix – Vectis…Source: id Quantix – Vectis…

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BB84 ProtocolBB84 Protocol

Source: id Quantix – Vectis…Source: id Quantix – Vectis…

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Using Uncertainty – Reality Using Uncertainty – Reality

Photon polarization is transformed Photon polarization is transformed through fiberthrough fiber Autocompensation – Faraday Autocompensation – Faraday

orthoconjugationorthoconjugation

No good single-photon emitterNo good single-photon emitter

No good single-photon detectorNo good single-photon detector

Quantum Error CorrectionQuantum Error Correction

Privacy AmplificationPrivacy Amplification

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Faraday orthoconjugationFaraday orthoconjugation

Source: Risk – BethuneSource: Risk – Bethune

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Single-Photon DetectorSingle-Photon Detector

Avalanche Photodiode (APD)Avalanche Photodiode (APD)

InGaAs APD used in ‘Geiger’ modeInGaAs APD used in ‘Geiger’ mode Reverse biased just below breakdown Reverse biased just below breakdown

idleidle Reverse biased just above breakdown Reverse biased just above breakdown

for 1nsfor 1ns Kept cool (e.g. 140K) to prevent Kept cool (e.g. 140K) to prevent

thermally-induced avalanchethermally-induced avalanche

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Single-Photon EmitterSingle-Photon Emitter

‘‘Approximated’ by attenuating a Approximated’ by attenuating a train of laser pulsestrain of laser pulses If attenuating to average power If attenuating to average power

matching a single photonmatching a single photon37% 0 photon – no information37% 0 photon – no information

37% 1 photon37% 1 photon

26% 2+ photons – security risk!26% 2+ photons – security risk!

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Single-Photon Emitter Single-Photon Emitter (Cont.)(Cont.)

Practical systems attenuate to 0.1 Practical systems attenuate to 0.1 photonphoton

89.5% 0 photon89.5% 0 photon

10% 1 photon10% 1 photon

0.5% 2+ photons0.5% 2+ photons

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BibliographyBibliographyRisk, W. P.; Bethune, D. S. – “Quantum Cryptography – Risk, W. P.; Bethune, D. S. – “Quantum Cryptography – Using Autocompensating Fiber-Optic Interferometers.” Using Autocompensating Fiber-Optic Interferometers.” Optics and Photonics NewsOptics and Photonics News. July 2002, pp 26-32. July 2002, pp 26-32id Quantique – “Quantis-OEM Datasheet.” v1.3, July 2004, id Quantique – “Quantis-OEM Datasheet.” v1.3, July 2004, http://www.idquantique.comhttp://www.idquantique.comid Quantique – “White Paper – Random Numbers Generation id Quantique – “White Paper – Random Numbers Generation using Quantum.” Version 2.0, August 2004, using Quantum.” Version 2.0, August 2004, http://www.idquantique.comhttp://www.idquantique.comid Quantique – “White Paper – Understanding Quantum id Quantique – “White Paper – Understanding Quantum Cryptography.” Version 1.0, April 2005, Cryptography.” Version 1.0, April 2005, http://www.idquantique.comhttp://www.idquantique.comWikipedia community – “Quantum Cryptography.” Wikipedia community – “Quantum Cryptography.” Wikipedia – The Free Encyclopedia. Wikipedia – The Free Encyclopedia. Viewed on April 12, Viewed on April 12, 2006. http://en.wikipedia.org/wiki/Quantum_cryptography2006. http://en.wikipedia.org/wiki/Quantum_cryptography