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Quantum Cryptography Post Tenebras Lux! Grégoire Ribordy.

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Presentation on theme: "Quantum Cryptography Post Tenebras Lux! Grégoire Ribordy."— Presentation transcript:

1 Quantum Cryptography Post Tenebras Lux! Grégoire Ribordy

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

3 Cryptography Document Key Encryption Decryption Document Key Secure communication Key transmission Alice Bob Eve Key generation

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

5 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

6 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

7 Another look at Moores Law Trend of computer chip development hit a « quantum wall » Potential of quantum physics not yet exploited in industrial applications

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

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

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

11 Classical vs quantum communications Communication System Secure channel over dedicated optical fiber –Absolute security guaranteed by the laws of quantum physics "0" "1" Fragile !

12 Quantum communications Transmitting information with a single-photon Light PolarizationLinear States = "0" = "1"

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

14 Eavesdropping (2) Communication interception Use quantum physics to force spy to introduce errors in the communication "0" Eve BobAlice

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

16 Quantum Cryptography Protocole BB84 A better name: Quantum Key Distribution

17 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

18 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

19 Implementing the quantum channel Necessary components Channel Single-Photon Source Single-Photon Detector

20 Quantum Cryptography System Collaboration: id Quantique – UniGe Pilot tests in 2003

21 Field tests Optical fibers Distance: 67 km Genève – Lausanne

22 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

23 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

24 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

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

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

27 Post Tenebras Lux?

28 Thank you for your attention id Quantique SA Chemin de la Marbrerie, 3 CH-1227 Carouge / Geneva Switzerland Ph: Fax:


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