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**Quantum Cryptography Post Tenebras Lux!**

Grégoire Ribordy Changer Logo A Quantum Leap for Cryptography Logo en bas ?

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**Outline Introduction: Cryptography Quantum Information Processing**

Quantum cryptography protocole Practical system Applications and outlook

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**Cryptography Eve Bob Alice Key transmission**

Document Document Secure communication Bob Key Key Decryption Encryption Alice Key transmission Logo en bas: sans slogan; slogan à droite Key generation

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**Secret key cryptography**

Encryption and decryption key identical Problem: Key exchange The longer the key, the higher the security One-time pad

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**Public key cryptography**

Encryption key Decryption key (public) (private) One way function Key distribution problem solved? Caution: vulnerable Mathematical progress: Security is based on mathematical assumptions Technological progress: Computers become more powerful 13 31 = 403

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**Computational complexity**

Complexity of a computer program… P(n) = n + n2 + n3+…+nk E(n) = exp (n) = n + n2 + n3 + n4 … + n In cryptography

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**Another look at Moore’s Law**

Trend of computer chip development hit a « quantum wall » Potential of quantum physics not yet exploited in industrial applications

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**Quantum Physics and Cryptography**

Public key cryptography cracking Eve Document Document Secure communication Bob Key Key Decryption Encryption Alice Key transmission Logo en bas: sans slogan; slogan à droite Key generation

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**Quantum Random Number Generator**

Physical randomness source Commercially available Applications Cryptography Numerical simulations Statistics Concurrence: logiciel QRNG (actuellement – 2e gén – application: SSL – contact avec fabriquant cartes crypto)

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**Quantum Physics and Cryptography**

Public key cryptography cracking Eve Document Document Secure communication Bob Key Key Decryption Encryption Alice Key transmission Logo en bas: sans slogan; slogan à droite Key generation

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**Classical vs quantum communications**

Communication System Secure channel over dedicated optical fiber Absolute security guaranteed by the laws of quantum physics "0" "1" Fragile ! Mentionner Heisenberg Limitation de la distance

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**Quantum communications**

Transmitting information with a single-photon Light Polarization Linear States = "0" = "1"

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Eavesdropping (1) A single-photon constitutes an elementary quantum system It cannot be split Semi-transparent mirror 50%

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**Eavesdropping (2) Communication interception**

Use quantum physics to force spy to introduce errors in the communication Alice Bob "0" "0" Eve

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**Polarization measurement**

Using polarizing filters to measure polarization states and and probabilistic modification But and ? Heisenberg’s Uncertainty Relations = "0" = "0" Base 1 Base 2 = "1" = "1"

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**Quantum Cryptography Protocole**

BB84 A better name: Quantum Key Distribution

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**Key Distillation (ideal case)**

Transmission Qubits Alice Bob Quantum channel Sifted key Reconciliation Basis QBER estimate 0 : no eavesdropping Reveals rather than prevents eavesdropping A better name: quantum key distribution QBER = > 0 : eavesdropping

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**Key Distillation (realistic case)**

Transmission Qubits Alice Bob Quantum channel (losses) Raw key Public channel Reconciliation Basis Sifted key QBER estimate correction Error amplification Privacy Key Key

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**Implementing the quantum channel**

Necessary components Channel Single-Photon Source Single-Photon Detector

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**Quantum Cryptography System**

Collaboration: id Quantique – UniGe Pilot tests in 2003

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Field tests Optical fibers Distance: 67 km Genève – Lausanne

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**Deployment Computer network A Computer network B Optical Fiber**

(classical channel) Optical Fiber (quantum channel) QKD Hardware QKD Hardware Traffic Network A to B Encrypted traffic Encryption Main features Encryption Transparent High-bit rate (1 Gbit/s) Remote monitoring Automated key management Classical channel Decryption Encrypted traffic Traffic Network B to A Quantum channel Key exchange

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**Applications Advantages Constraints**

Automated key management Long term security Constraints Optical fiber Distance < 100 km High-security applications in a metropolitan area network Financial sector, e-government Storage, disaster recovery

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**Extending the distance**

Secure relays Improved components Photon counting detectors Photonic crystal fibers: 0.2 dB/km 0.02 dB/km Quantum repeater Free-space links to satellites

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**Quantum Repeater Quantum Teleportation Rudimentary quantum repeater**

Quantum version of a fax Recently at Unige: teleportation of a photon over 2km Rudimentary quantum repeater

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**Free-space QKD Satellites = secure relay**

Experiments over horizontal links 23.4 km in the German Alps Tokyo Genève

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Post Tenebras Lux?

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**Thank you for your attention**

id Quantique SA Chemin de la Marbrerie, 3 CH-1227 Carouge / Geneva Switzerland Ph: Fax:

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