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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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Presented By, Mohammad Anees SSE, Mukka. Contents Cryptography Photon Polarization Quantum Key Distribution BB84 Protocol Security of Quantum Cryptography.

Presented By, Mohammad Anees SSE, Mukka. Contents Cryptography Photon Polarization Quantum Key Distribution BB84 Protocol Security of Quantum Cryptography.

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