1. Quantum Cryptography Post Tenebras Lux!
Grégoire Ribordy
Changer Logo  A Quantum Leap for Cryptography
Logo en bas ?

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

3. 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

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
13  31 = 403

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

7. 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

8. 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

9. 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)

10. 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

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 !
Mentionner Heisenberg
Limitation de la distance

12. Quantum communications
Transmitting information with a single-photon
Light Polarization
Linear 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
Alice
Bob
"0"
"0"
Eve

15. 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"

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

17. 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

18. 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

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 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

23. 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

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

26. Free-space QKD Satellites = secure relay
Experiments over horizontal links
23.4 km in the German Alps
Tokyo
Genève

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: