This document outlines a presentation on quantum key distribution. The presentation covers an introduction to cryptography, classical cryptography techniques like the one-time pad, quantum cryptography concepts like photon polarization, and quantum key distribution protocols like BB84. Quantum key distribution allows two parties to detect an eavesdropper attempting to gain knowledge of an encrypted key by exploiting quantum effects. The document provides context and details for each topic that will be covered in the presentation.

1. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Quantum Key Distribution In Quantum
Cryptography
Shahrukh Ayaz Khan
Seminar Presentation
SSBT’s College of Engineering & Technology,
Bambhori, Jalgaon - 425 001, Maharashtra, India
October 6, 2015
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2. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Presentation Outline
1 Introduction
2 Classical Cryptography
3 Quantum Cryptography
4 Quantum Key Distribution
5 Pros and Cons
6 Conclusion
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3. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Outline
1 Introduction
2 Classical Cryptography
3 Quantum Cryptography
4 Quantum Key Distribution
5 Pros and Cons
6 Conclusion
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4. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
What is Cryptography?
Cryptography: the coding and decoding of secret
messages.
Cryptography is the art of rendering a message
unintelligible to any unauthorized party
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(Korean)
It is part of the broader field of cryptology, which also
includes cryptoanalysis, the art of code breaking
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5. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Need For Cryptography
Suppose Alice want to send a secret message to his friend
Bob over an insecure channel
we have to prevent Eve from Eavesdropping on
communication between Alice and Bob.
Figure: Meet Alice and Bob
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6. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Outline
1 Introduction
2 Classical Cryptography
3 Quantum Cryptography
4 Quantum Key Distribution
5 Pros and Cons
6 Conclusion
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7. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Cryptography
What is key?
Encryption is combine a message with some additional
information - known as the key and produce a
cryptogram.
Decryption is combine a cryptogram with some additional
information - known as the key and produce a message.
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8. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Types of Cryptosystems
Symmetric - use the same (secret) key to encrypt and
decrypt a message
Asymmetric - use one key (the public key) to encrypt a
message and a different key (the private key) to decrypt it.
Asymmetric cryptosystems are also called public key
cryptosystems.
Figure: Process of cryprography
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9. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
One-Time Pad
first proposed by Gilbert Vernam in 1926
This cryptosystem is thus provably secure in the sense of
information theory (Shannon 1949)
Actually, this is today the only provably secure
cryptosystem
Only problem is distributing the keys and it is Difficult to
implement
Figure: One time pad
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10. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Outline
1 Introduction
2 Classical Cryptography
3 Quantum Cryptography
4 Quantum Key Distribution
5 Pros and Cons
6 Conclusion
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11. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Need of Quantum Cryptography?
The problem of distributing the keys in the OTP is
overcomed in Quantum Key Distribution
Using quantum effects, we can distribute keys in perfect
secrecy!
The Result is Perfect Cryptosystem, QC = QKD + OTP
Classical Cryptography relies heavily on the complexity of
factoring integers.
Quantum Computers can use Shors Algorithm to
efficiently break todays cryptosystems
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12. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Quantum Elements
Quantum Mechanics depends on 2 major elements of quantum
mechanics: i.e heisenberg uncertainity principle and principle of
photon polarization.
Heisenberg uncertainty principle : states that certain pairs
of physical properties are related in such a way that
measuring one property prevents the observer from
simultaneously knowing the value for other.
Principle of photon polarization: tells that an
eavesdropper cannot copy unknown Qubits due to
non-cloning algorithm.
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13. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Overview of Quantum Cryptography
Unique property of quantum cryptography is the ability of
two communicating users to detect the presence of third
party trying to gain knowledge of the key.
By using quantum superposition/entanglement and
transmitting information in quantum states , a
communication system can be implemented which can
detect eavesdropping.
The polarization basis is the mapping we decide to use for
a particular state
Entangled pairs of photon are used that affects
randomness of measurements
Figure: Photon Polarization using BasesApril 10, 2015 Shahrukh Ayaz Khan Quantum Key Distributionl 13/26

14. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Outline
1 Introduction
2 Classical Cryptography
3 Quantum Cryptography
4 Quantum Key Distribution
5 Pros and Cons
6 Conclusion
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15. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Quantum Key Distribution
Quantum Key Distribution exploits the effects discussed in
order to thwart eavesdropping.
It enables two parties to produce a shared random bit
string known only to them, which can be used as a key for
encryption and decryption.
If an eavesdropper uses the wrong polarization basis to
measure the channel, the result of the measurement will
be random.
There are three main security protocols for QKD: BB84,
B92, and Entanglement-Based QKD.
We will only discuss BB84 here.
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16. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
BB84
BB84 was the first security protocol implementing
Quantum Key Distribution.
The key consists of bits that will be transmitted as
photons.
Each bit is encoded with a random polarization basis!
Alice and Bob talk on the telephone:
Alice chooses a subset of the bits (the test bits) and
reveals which basis she used to encode them to Bob.
Bob tells Alice which basis he used to decode the same
bits.
Where the same basis was used, Alice tells Bob what bits
he ought to have got.
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17. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
BB84 with no Eavesdropping
The test bits allow Alice and Bob to test whether the channel
is secure.
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18. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Cont..
Figure: Getting the Final Key
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19. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
BB84 with Eavesdropping
If an eavesdropper Eve tries to tap the channel, this will
automatically show up in Bobs measurements.
In those cases where Alice and Bob have used the same
basis, Bob is likely to obtain an incorrect measurement
As Eve intercepts Alices photons, she has to measure them
with a random basis and send new photons to Bob.
The photon states cannot be cloned (non-cloneability).
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20. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Outline
1 Introduction
2 Classical Cryptography
3 Quantum Cryptography
4 Quantum Key Distribution
5 Pros and Cons
6 Conclusion
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21. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Merits
Nearly Impossible to steal
Detect if someone is listening
Secure
Limitations
Price limits length,signal is absorbed, noise increased
Availability
Compete with traditional networks
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22. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Future Scope
Future applications are in the most secure communication lines
for bank-to-ATM transactions, financial information protection
over the internet, and military and government communications
including the use for ship-to-ship, ground-to-satellite, and
satellite-to-satellite communication.
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23. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Outline
1 Introduction
2 Classical Cryptography
3 Quantum Cryptography
4 Quantum Key Distribution
5 Pros and Cons
6 Conclusion
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24. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Conclusion
Quantum cryptography is a major achievement in security
engineering.
As it gets implemented, it will allow perfectly secure bank
transactions, secret discussions for government officials,
and well-guarded trade secrets for industry!
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25. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
References
1 N. Namekata, S. Mori, and S. Inoue, Quantum key
distribution over an installed multimode optical fiber local
area network, Optical Express, 2015.
2 A. Beresford and F. Stajano, Location privacy in pervasive
computing, IEEE Pervasive Computing, 2011.
3 K. G. Paterson, F. Piper, and R. Schack, Why quantum
cryptography?, Quantum physics, quant-ph/0406147,
June 2004.
4 Hidema Tanaka, Security Analysis of Generalized
Confidential Modulation for Quantum Communication
International Journal of Computer Networks &
Communications (IJCNC) Vol.5, No.5, September 2013
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26. Quantum Key
Distribution
Outline
Introduction
Classical
Cryptography
Quantum
Cryptography
Quantum Key
Distribution
Pros and Cons
Conclusion
Thank You...
ShahrukhA.Khan
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