quantum cryptography post tenebras lux! grégoire ribordy
TRANSCRIPT
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Quantum CryptographyPost 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
0101110100011011
Document
KeyEncryption
Decryption0101110100011011
Document
KeySecure communication
Key transmission
AliceBob
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
La Poste
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
Key length
Co
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tim
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EncryptionDecryption
Key length
Co
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tim
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Decryption(without key)
Key length
Co
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Theoretical progress
Key length
Co
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tim
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Quantum computer
Classical computer
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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
1
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1970 1980 1990 2000 2010 2020
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Quantum Limit
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Quantum Physics and Cryptography
0101110100011011
Document
KeyEncryption
Decryption0101110100011011
Document
KeySecure communication
AliceBob
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
0101110100011011
Document
KeyEncryption
Decryption0101110100011011
Document
KeySecure communication
Key transmission
AliceBob
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""1" Fragile !
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Quantum communications Transmitting information with a single-photon
E
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%
50%
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Eavesdropping (2) Communication interception
Use quantum physics to force spy to introduce errors in the communication
?"0" "0"
Eve
BobAlice
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Polarization measurement Using polarizing filters to measure polarization states
and
and
and ?
= "0"
= "1"
= "0"
= "1"Base 1 Base 2
But• probabilistic
• modification
Heisenberg’s Uncertainty Relations
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Quantum Cryptography Protocole BB84
A better name: Quantum Key Distribution
A lice 's B it S e q u e n c e
0 1 0 - 0 1 1 1 1 - 1 0
- 1 - - 0 1 - - 1 - 1 0
B o b 's B a s e s
B o b 's R e s u lts
K e y
A lice
B o b
P o la riz e r s
H o r iz o n ta l - Ve rtic a l
D ia g o n a l ( -4 5 , + 4 5 )
H /V B a s is
4 5 B a s is
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Key Distillation (ideal case)
Alice BobQuantum channel
Qubits
Transmission
Basis
Reconciliation
QBERestimate
QBER =0 : no eavesdropping
> 0 : eavesdropping
Sifted key
Reveals rather than prevents eavesdropping
A better name: quantum key distributionquantum key distribution
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Key Distillation (realistic case)
Alice BobQuantum channel
Public channel
(losses)
Qubits
Transmission
Basis
Reconciliation
QBERestimate
Error
correctionPrivacy
amplification
Sifted key
Raw key
Key Key
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Implementing the quantum channel Necessary components
ChannelSingle-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 QKD Hardware
Optical Fiber(classical channel)
Computernetwork A
Computernetwork B
Key exchange
Quantum channel
Encryption
Decryption
Classical channel
Traffic Network A to B
Traffic Network B to A
Encryptedtraffic
Encryptedtraffic
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
01100111010101000110010
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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
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CH-1227 Carouge / Geneva
Switzerland
Ph: +41 22 301 83 71
Fax: +41 22 301 83 79
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