Quantum Cryptography and QKD

1. Presented by:
Shahzad Ahmad
M.tech-2nd Year(CIS)
18LECM066

2.  What is Cryptography?
 History of Quantum Cryptography
 Quantum Cryptography
 Heisenberg Uncertainty principle
 Polarization of Photon
 Quantum Communication Block Diagram
 Quantum key Distribution Protocol
 Implementing Quantum Cryptography
 Advantages & Disadvantages
 Conclusion
 References
CONTENTS :

3. WHAT IS CRYPTOGRAPHY?
• Cryptography(derived from Greek word kryptós “hidden secret”
and graphein, "to write“) is the science of codes and ciphers.
Fig.1 Block Diagram Of Cryptography[1]

4. Fig. 2 -Block Diagram Of Cryptography[2]

5. OTP (ONE TIME PAD)
• One-time pad (OTP) is an encryption technique that cannot
be cracked if used correctly.
• The key used in a one-time pad is called a secret key.
• The problem raises how to get the key to the decrypting
party safely or how to keep both keys secure.
• One-time pads are “information theoretically secure".

6. Fig. 3-OTP Example
(William Stalling,Cryptography And Network Security,edition 4th)

7. • Quantum cryptography is an emerging technology in which
two parties can secure network communications by applying
the phenomenon of quantum physics.
• It uses photon and photon’s polarization which is their
quantized properties to encode the information .
• QKD is a promising technique that ensures unconditionally
secure distribution of a secret key, between two end points.
Quantum Cryptography :

8. • First proposed by Stephen Wiesner in 1969.
• Bennet and Brassard proposed the Quantum key distribution
Protocol in 1984.
• In 1991, Artur Ekert, developed a different approach to QKD
based on peculiar quantum correlations i.e. known as
quantum entanglement.
HISTORY OF QUANTUM CRYPTOGRAPHY :

9. • Quantum Cryptography is combination of OTP and QKD.
• QKD offers an information-theoretically secure solution to the
key exchange problem.
• Quantum cryptography is based on two important principles-
i. Heisenberg’s uncertainty principle
ii. Polarization of Photon
QUANTUM CRYPTOGRAPHY

10. • It could be used for cryptography was first devised by Stephen
Wiesner, a physicist in 1969.
• It state that the observer simultaneously cannot measure two
physical properties which are related with each other.
• With regards to this definition , two examples are referred-
i. For a particle P, two physical properties i.e. position and the
Momentum cannot be calculated simultaneously.
ii. The measurement of a photon cannot be done in rectilinear
basis and diagonal basis simultaneously.
HEISENBERG’S UNCERTANITY PRINCIPLE :

11. • The process of transforming unpolarized light into
polarized light is known as polarization.
Fig. 4- Polarization of Photon
(Resnick Halliday,Principles Of Physics,edition9th)
POLARIZATION OF PHOTON :

12. • The photon is polarized in one of the basis to represent a bit
known as a Qubit.
• In Polarization of Photons replica of qubits is not possible
according to the No Cloning Theorem.
• The use of Photons leads to the evolution of Quantum
Cryptography.

13. • Polarization of photon is done in rectilinear basis and diagonal
basis to represent binary bits .[4]
Polarizatio
n
Basis Binary
bit
0° Rectilinear 0
90° Rectilinear 1
45° Diagonal 0
135° Diagonal 1
Figure.5
Polarization of Photons To Represent Bits :

14. • A bit can be in the state 0 or 1 whereas a qubit can occur in the
state |0⟩ or |1⟩ .
• Superposition state is noted as: |ψ⟩=α|0⟩+β|1 ⟩
• The probability of obtaining |ψ⟩ in |0⟩ state is |α|2 and the
probability of obtaining |ψ⟩ in |1 ⟩ state is |β|2.
• The probability of getting result of a measurement is obtained by
squaring the coefficients.
The condition is |α|2 + |β|2 = 1
QUBITS AND QUANTUM STATES :

15. • The state can be written by stacking the two complex number
which is a two-dimensional complex unit vector.
CONTD….
𝛼
𝛽
|0⟩ =
1
0
where α=1, 𝛽=0 |1⟩ =
0
1
where α=0, 𝛽=1
Where, |ψ⟩ = cosθ |0⟩+ sinθ |1 ⟩=
𝑐𝑜𝑠θ
𝑠𝑖𝑛θ
Figure.6 [4]

16. • Notation 1 and 2 are state 0° and state 90° in rectilinear basis
respectively.
• Notation 3 and 4 are state 45°and state 135° in diagonal basis
respectively.
Notation Of Quantum State :
1
√2
( |0⟩ + |1⟩ ) = | / ⟩
1
√2
( |0⟩ - |1⟩ ) = | ⟩
1. |0⟩ = |−⟩
2. |1⟩ = | ⃓ ⟩
3.
4.

17. PROBABILITY OF A PHOTON :
1. Probability of a photon transmitted and
produced in same basis and same state
2. Probability of a photon transmitted and
produced in same basis but different stat
3. Probability of a photon transmitted and
produced in different basis
4. Probability of a photon transmitted in
one basis and produced at an angle
Figure.7 [4] Figure.8 [4]
Figure.9 [4] Figure.10 [4]

18. • Message is send through the public channel while key is send
through quantum channel.
Figure.11 Quantum Communication [5]
QUANTUM COMMUNICATION:

19. QUANTUM KEY DISTRIBUTION PROTOCOLS:
• It is a secure communication method which implements a crypto-
graphic protocol involving components of quantum mechanics.
• QKD can detect any eavesdropping.
• QKD is only used to produce and distribute a key, not to transmit
any message data.
• QKD Protocols are various type-
i. BB84 Protocol
ii. B92 Protocol
iii. Six state Protocol

20. • BB84 was the first security protocol implementing Quantum Key
Distribution.
• This protocol depended on Heisenberg Uncertainty principle.
• It uses the idea of photon polarization.
• Communicating parties uses two communication channels –
i. classical channel and
ii. a quantum channel
• Qubits transmitted on the quantum channel and the conventional
messages transmitted on classical channel.
BB84 PROTOCOL :

21. Figure.12 BB84 Protocol[5]
CONTD….

22. • It is a modified protocol of BB84 with two states.
• A photon polarization of 0° in the rectilinear basis is used to
represent binary 0 and 45° in the diagonal basis is binary 1.
B92 PROTOCOL :
Figure.13 [5]

23. SIX-STATE PROTOCOL (SSP) :
• SSP uses six states on three orthogonal basis to encode the
bits which are required for communication between entities.
• The probability of using one of the basis equals 1/3.
Figure.14[5]

24. Implementing Quantum Cryptography :
• BBN, Harvard, and Boston University built the DARPA quantum
network , the world's first network that delivers end-to-end
network security via high-speed quantum key distribution.
• This network is suitable for deployment in metro-size areas via
standard telecom fiber.
• The DARPA security model is the cryptographic virtual private
network (VNP).

25. DISADVANTAGES ::
• While traveling through the channel (i.e. optical fiber or air)there is
possibility of change in polarization of photon due to various
causes.
• Need of dedicated channel is must between source and
destinations which implies high cost.
ADVANTAGES :
• Used to detect eavesdropping in QKD (Quantum Key Distribution).
• Virtually unhackable.

26. CONCLUSION:
:
• Quantum Cryptography has the potential to make a valuable
contribution to the network security among government,
businesses and academic sectors.
• Prominent technology wherein two entities can communicate
securely with the sights of quantum physics.
• QKD offers unconditionally secure communication based on
quantum mechanics .
• Integration of Quantum Cryptography in Wireless Networks
has great prospective in terms of better network security.

27. REFERENCES :
[1] Roger A. Grimes, “Cryptography Apocalypse: Preparing for the Day When
Quantum Computing Breaks Today’s Crypto”,Wiley-2020
[2] Jintai Ding ,Rainer Steinwandt, “Post-Quantum Cryptography”: 10th
International Conference, Springer, May 2019
[3] Mahdi H. Al Hasani,Kais A. Al Naimee, “Impact security enhancement in
chaotic quantum cryptography”,Elsevier, June 2019
[4] Laszlo Gyongyosi, Laszlo Bacsardi, “A Survey on Quantum Key
Distribution”:IEEE Infocommunication Journal Vol. XI,2019
[5] V. Padamvathi , B. Vishnu Vardhan , A.V.N. Krishna, " Quantum Cryptography
and Quantum Key Distribution Protocols: A Survey “,IEEE 6th International
Conference on Advance Computing , Feb 2016.
[6] C.H.Bennett, and G. Brassard, " Quantum Cryptography: Public key
distribution and coin tossing ",Theoretical Computer Science, Elseiver, vol.
560, 2014.

28. [7] R.Goel , M.Garuba , A.Girma, " Research Directions in Quantum
Cryptography", IEEE fourth International Conference on Information
Technology, April 2007.
[8] M.S. Sharbaf , " Quantum Cryptography: “A New Generation of Information
Technology Security System " ,IEEE Sixth International Conference on
Information Technology, April 2009.