quantum cryptography beyond the buzz grégoire ribordy cern, may 3rd 2006
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Quantum CryptographyQuantum CryptographyBeyond the buzzBeyond the buzz
Grégoire RibordyCERN, May 3rd 2006
2www.idquantique.com
OutlineOutline
Quantum physics and information technology
The limits of classical cryptography
The principles of quantum cryptography
Practical systems and applications
Future directions
3www.idquantique.com
Moore’s law and quantum physicsMoore’s law and quantum physics
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Quantum Limit
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Classical and Quantum physicsClassical and Quantum physics
Classical physics … - 1900 Describes the macroscopic world
Deterministic
Intuitive
Quantum physics 1900 - … Description of the microscopic
world
Probabilistic Central role of the observer Not very intuitive
Quantum physics Novel information processing possibilities Quantum Information Theory (QIT)
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Generating random numbers with quantum physicsGenerating random numbers with quantum physics
High bit rate• 4 or 16 Mbits/s
Continuous monitoring
Main OS’s supported
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OutlineOutline
Quantum physics and information technology
The limits of classical cryptography
The principles of quantum cryptography
Practical systems and applications
Future directions
7www.idquantique.com
M essage
Public Key
ScrambledM essage
M essage
Private Key
Different Keys
Message
Secret Key
ScrambledMessage
Message
Secret Key
Identical keysKey Exchange ?!?
Introduction: Classical CryptographyIntroduction: Classical Cryptography
Secret Key Cryptography
Public Key Cryptography
Alice
Bob
Different keys Key exchange solved
Vulnerabilities!!!
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Key length
Co
mp
uti
ng
tim
e
Decryption(without key)
Security of public key cryptographySecurity of public key cryptography
EncryptionDecryption (with key)
Selected Key Length
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Vulnerabilities of public key cryptographyVulnerabilities of public key cryptography
Key length
Co
mp
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ng
tim
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Classical computer
Selected Key Length
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Vulnerabilities of public key cryptographyVulnerabilities of public key cryptography
Key length
Co
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tim
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Quantum computer
Classical computer
& Theoretical progress
Selected Key Length
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Where does Quantum Cryptography fit in?Where does Quantum Cryptography fit in?
Message
Secret Key
ScrambledMessage
Message
Secret Key
Alice
Bob
Quantum Cryptography is a key distribution technique!
Quantum Key Distribution is a better name!!!
Secret key exchange by quantum cryptography
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OutlineOutline
Quantum physics and information technology
The limits of classical cryptography
The principles of quantum cryptography
Practical systems and applications
Future directions
13www.idquantique.com
Physical implementation of a data channelPhysical implementation of a data channel
Fragile !"0"
"1""1"
Classical communication Quantum communication
Security guaranteed by the laws of quantum physics
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Quantum Cryptography: rules of the gameQuantum Cryptography: rules of the game
1. Details of the protocole publicly known
2. Goal: to produce a secret key or nothing
« Eve cannot do better than cutting the line »
Alice and Bob: to estimate Eve’s information on key
IAE small: Produce a key
IAE large:
k’
Eve
Quantum channel
Classical channel
QUANTUM KEY DISTRIBUTION
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Polarization of PhotonsPolarization of Photons
Direction of oscillation of the electric field associated to a lightwave
Polarization states
What can we do with it ?
50 %
E
50 %
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Irreversibility of MeasurementsIrreversibility of Measurements
Incoming photon polarized at 90
Incoming photon polarized at 45
50 %
Rotation of polarizer
50 %
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Quantum communicationsQuantum communications
Transmitting information with a single-photon
Use a quantum property to carry information
Liner States
= "0" = |0>
= "1" = |1>
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Eavesdropping (1)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)Eavesdropping (2)
Communication interception
Use quantum physics to force spy to introduce errors in the communication
?|0> |0>
Eve
BobAlice
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Quantum Cryptography ProtocoleQuantum 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
0
0
0
0
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Eavesdropping (3)Eavesdropping (3)
50% 50%
50%50%
50% 50% 50%50%
Bob
Eve
Ok Ok OkErrorError
Alice
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Key Distillation (ideal case)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)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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Information curvesInformation curves
0.40.0
Sh
an
no
n In
form
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0.1 0.2 0.30.0
0.2
0.4
0.6
0.8
1.0
QBER
)(1 QBERHI AB
IAEOpt. indiv. attack
Secret key rate
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The Principles of Quantum Cryptography: SummaryThe Principles of Quantum Cryptography: Summary
Quantum CommunicationQuantum CommunicationRaw key exchangeRaw key exchange
Integrity VerificationIntegrity VerificationKey DistillationKey Distillation
Key UseKey Use
Quantum Cryptography
Conventional SymmetricCryptography
Point-to-point optical link
Future-proof key exchangewith security guaranteed bythe laws of physics
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OutlineOutline
Quantum physics and information technology
The limits of classical cryptography
The principles of quantum cryptography
Practical systems and applications
Future directions
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Building a Quantum Key Distibution SystemBuilding a Quantum Key Distibution System
Necessary components
“System approach”
ChannelSingle-Photon Source
Single-Photon Detector
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Polarization CodingPolarization Coding
Typical system
LD 1
LD 2
LD 3
LD 4
QuantumChannel
Alice BobBasis 1
Basis 2
/2
PBS
PBS
"0"
"1""0"
Waveplates
BS
BS
BS F "1"
APD
APD
Public Channel
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InterferencesInterferences
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InterferometerInterferometer
Classical interference
Port 1
Port 2
E
1E
2E
0
0.5
1
0 2 4 6
Phase [radians]
Sortie 1
Sortie 2
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Phase encodingPhase encoding
Quantum optics: single-photon
A
B
A lic e
B o b
D 2
D 10
0.5
1
0 2 4 6
Phase [radians]
Output 1
Output 2
Base 1: A = 0;
Base 2: A =
Basis choice: B = 0;
Compatible: Alice A Di
Bob Di A(A-B = n)Bas
es Incompatible: Alice and Bob ??
(A-B = )
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Phase encoding (2)Phase encoding (2)
Stability of such system ???
In practice
A
B
A lic e
B o b
D 2
D 1
10 km
10 km ± /10 (100 nm)
A lice
A B
B o b
Time (ns)
LL
0
20
40
60
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CC
-3 -2 -1 0 1 2 3
CL + LC
+
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Auto-compensated set-upAuto-compensated set-up
Time multiplexing
A lice
B obA
B
A tt .S h o r t a rm
L o n g a rm
M F
S P
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Practical requirementsPractical requirements
Distance limitation < 100 km
Current range is sufficient for a vast majority of MAN/SAN applications
Point-to-point dark fiber• Amplifiers• Opto-electro-opto conversion
perturbation of the quantum state of the photon
Distance
Signal, Noise
pnoise
psignal
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Link Encryptors with QKDLink Encryptors with QKD
Network Appliance• Point-to-point link encryption
• Layer 2 device
• Network protocole independent
• Compatible with higher layer encryption
Specifications- Encryption: AES (128, 192, 256 bits)- Key rate as high as 100 keys / s- Distance < 100 km (60 miles)- Pair of dark fiber
Target ApplicationsMAN or SAN encryption
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« Swiss Quantum » Pilot Site« Swiss Quantum » Pilot Site
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OutlineOutline
Quantum physics and information technology
The limits of classical cryptography
The principles of quantum cryptography
Practical systems and applications
Future directions
38www.idquantique.com
Extending the key distribution distanceExtending the key distribution distance
Chaining links
Better components
Free space links to low-earth-orbit (LEO) satellites
Quantum relays and repeaters
Tokyo Geneva
A BB' A ' B" A" B'" A '"
Telco Infrastructure
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Compatibility with conventional optical networksCompatibility with conventional optical networks
Optical switching
WDM Links
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Thank you very much for your attentionThank you very much for your attention
id Quantique SA
Chemin de la Marbrerie, 3
CH-1227 Carouge
Switzerland
Ph: +41 22 301 83 71
Fax: +41 22 301 83 79
info@idquantique.com
www.idquantique.com
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Optical TapsOptical Taps
Optical taps are cheap and simple to use
« Tapping a fibre-optic cable without being detected, and making sense of the information you collect isn’t trivial but has certainly been done by intelligence agencies for the past seven or eight years. These days, it is within the range of a well funded attacker, probably even a really curious college physics major with access to a fibre optics lab and lots of time on his hands. »
John Pescatore, former NSA Analyst
The submarine « USS Carter » worth $4.1 bn will be able to tap and eavesdrop undersea cables.
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Key useKey use
The key produced by a quantum cryptography system is used with conventional symmetric encryption algorithms• One-time pad « unconditional security »
• Other symmetric algorithms (AES, Tripe-DES, etc.) enhanced security by frequent key change
Why is Quantum Cryptography not used to transmit data?1) Quantum Cryptography cannot guarantee that one particular bit will
actually be received.With a random key, it is not a problem. With data, it is.
2) Quantum Cryptography does not prevent eavesdropping, but reveals it a posteriori. Sending a key and verifying its secrecy allows to prevent information leakage.
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Device AuthenticationDevice Authentication
Initial key
Quantum Cryptography Session n: key material
Authentication keyEncryption/decryption key
Session nAuthentication key n
Au
the
ntic
atio
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refre
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