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Quantum Cryptography Post Tenebras Lux! Grégoire Ribordy

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Outline Introduction: Cryptography Quantum Information Processing Quantum cryptography protocole Practical system Applications and outlook

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Cryptography Document Key Encryption Decryption Document Key Secure communication Key transmission Alice Bob Eve 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 = 403

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Computational complexity Complexity of a computer program… P(n) = n + n 2 + n 3 +…+n k E(n) = exp (n) = n + n 2 + n 3 + n 4 … + n In cryptography

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Another look at Moores 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 Document Key Encryption Decryption Document Key Secure communication Alice Bob Eve Key generation Public key cryptography cracking Key transmission

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Quantum Random Number Generator Physical randomness source Commercially available Applications –Cryptography –Numerical simulations –Statistics

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Quantum Physics and Cryptography Document Key Encryption Decryption Document Key Secure communication Key transmission Alice Bob Eve Key generation Public key cryptography cracking

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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 !

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Quantum communications Transmitting information with a single-photon Light PolarizationLinear 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 "0" Eve BobAlice

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Polarization measurement Using polarizing filters to measure polarization states and ? = "0" = "1" = "0" = "1" Base 1Base 2 But probabilistic modification Heisenbergs Uncertainty Relations

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Quantum Cryptography Protocole BB84 A better name: Quantum Key Distribution

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Key Distillation (ideal case) AliceBob Quantum channel Qubits Transmission Basis Reconciliation QBER estimate QBER = 0 : no eavesdropping > 0 : eavesdropping Sifted key Reveals rather than prevents eavesdropping quantum key distribution A better name: quantum key distribution

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Key Distillation (realistic case) AliceBob Quantum channel Public channel (losses) Qubits Transmission Basis Reconciliation QBER estimate Error correction Privacy amplification Sifted key Raw 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 QKD Hardware Optical Fiber (classical channel) Computer network A Computer network B Key exchange Quantum channel Encryption Decryption Classical channel Traffic Network A to B Traffic Network B to A Encrypted traffic Encrypted traffic Optical Fiber (quantum channel) Main features - Encryption - Transparent - High-bit rate (1 Gbit/s) - Remote monitoring - Automated key management

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Applications Advantages –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 Teleportation –Quantum version of a fax –Recently at Unige: teleportation of a photon over 2km Rudimentary quantum repeater Quantum Repeater

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Free-space QKD Satellites = secure relay Experiments over horizontal links –23.4 km in the German Alps GenèveTokyo

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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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