# QUANTUM output of a vertical spin and if diagonal

QUANTUM CRYPTOGRAPHY
Vinayak Mitty
002-80-5522
University of
the Cumberlands

Introduction

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According to physics, Quantum is the minimum amount of any
physical entity involved in an interaction. Quantum refers to fundamental
behavior of smallest particles of matter. Quantum cryptography is a
cryptographic system that is built based on the knowledge of physics. This is a
robust type of cryptography which relies more on the concepts of physics than
on mathematics.

How
it Works

Quantum Cryptography uses photons to generate cryptographic
keys and transmit it to a receiver using suitable communication channel. A
photon is the smallest particle of light, which can spin in horizontal,
vertical and diagonal direction. It can spin also in all three directions at
the same time. The angle of movement or vibration of a photon is called
polarization of a photon. A polarizer is a filter that permits certain photons
with same oscillation and lets others pass through in changed state of
oscillation.

According to Heisenberg’s uncertainty principle, it is
impossible to measure the speed and position of a particle simultaneously with
high accuracy and its state will change when measured. In terms of
cryptography, if someone tries to intercept the transmitted photons, photons
pass through polarizer and the intended receiver gets a wrong photon, this
detects the interception. For example – if rectilinear polarization is used,
then a horizontal spin gives output of a vertical spin and if diagonal
polarization is used then left diagonal spin gives the output of right diagonal
spin, if there any interception, then the system wouldn’t give out the intended
output to the recipient thus detecting the interception.

For data transmission, each spin of photon is assigned a
binary value of 0 or 1. Below table gives an example of cryptographic key
generated using this method –

Polarization

X

X

+

+

X

+

+

+

X

X

Spin

/

|

|

|

Value

0

1

0

1

1

0

0

0

0

1

Note:

X is diagonal Polarization and + is rectilinear polarization;
and / represents left and right diagonal spin; | and ­­­­- represent vertical
and horizontal spin.

In this example, four polarization detectors – horizontal,
vertical, left diagonal and right diagonal are used to generate the key –
0101100001. This binary code can be converted to other formats such as string
and integer. This key is sent to the intended recipient using optical fiber
cables. The recipient applies random polarization and notes the applied
polarization, spin and value. Once the transmission is completed, the sender
and recipient communicate via a platform which need not be encrypted to verify
the message.

Quantum computing pose a great deal of threat to the encryption
methods that are used today, however, quantum cryptography could be the key to
strong and secure information security systems in the future. Many studies and
researches are being done on Quantum Key distribution (QKD) and ways to improve
it are being developed.

Differences

Cryptography

Quantum
Cryptography

Uses mathematical techniques to restrict
decryption

Uses
the concepts of quantum mechanics to avoid and detect interception

Fully supports Digital signature

Does not support digital
signature

Does not have this limitation

Has a
limitation on transmission distance – it cannot exceed 90-95 miles and optic
fiber supports even lesser transmission distance

It is not as strong as Quantum Cryptography in
detecting interference

Eavesdropping can be easily
detected

Conclusion

Quantum cryptography can revolutionize current cryptographic
systems and give us secure information systems. Research paper – Quantum
cryptography: public key distribution and coin tossing, by Charles Bennet and
Gilles Brassard provides a clear understanding of ‘What is Quantum
Cryptography’. The authors talk about properties of polarized photons, Quantum
key distribution and working of a quantum encryption system.