Quantum Crytography Ppt

7/30/2019 Quantum Crytography Ppt

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SAVITA RANA

5508426

I.T 6th SEM


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Cryptographyis the science of keeping privateinformation from unauthorized access, ofensuring data integrity and authentication, andother tasks.


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The process

Sender Plaintext

Cryptotext

Decryption

PlaintextRecipient

Message encryption

Key

Key ready for use

Secure key distribution

Encryption

Securetransmission

Hard Problem for conventional

encryption


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Encryption algorithm and related keys are kept secret.

Breaking the system is hard due to large numbers of possible

keys. The fundamental difficulty is key distribution to parties who want

to exchange messages.


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MODERN CRYPTOGRAPHY Public Key Cryptography(PKC) is the modern

cryptography.

In 1970s PKC emerged. Each user has two mutually inverse keys,

Encryption key is published.

Decryption key is kept secret.Anybody can send message to Bob but Bob can

only read.


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Better named Quantum key distribution.

Two physically separated parties can create and share

random secret keys.Allows them to verify that key has not been

intercepted


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Basic Idea


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History of QKD Stephen Wiesner in early 1970s wrote paper conjugate

coding

Paper by Charles Bennett and Gilles Brassard in 1984 is

the basis for QKD protocol BB84. The prototypedeveloped in 1991.

Another QKD protocol was developed by Artur Ekertin 1991.


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Heisenberg Uncertainty Principle Certain pairs of physical properties are related to each

other in such a way that measuring one propertyprevents the observer from knowing the value of theother. When measuring the polarization of photon,thechoice of what direction to measure effects allsubsequent measurements.


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Photon Polarization

Vertical filter

Tilted filter at

the angle

The probability of a photon appearing after the second

filter depends on the angle and becomes 0 at= 90 degrees.

The first filter randomizes the measurements of thesecond filter.


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Binary information Each photon carries one qubit of information.

Polarization can be used to represent a 0 or 1.

In quantum computation this is called qubit.


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Contribution of Quantum cryptographyMain contribution are:

It solved the key distribution problem.

Unconditionally secure key distribution methodwas proposed by the Charles Bennett and GillesBrassard in 1984. The method is called BB84.

Once key is securely received it can be used to

encrypt the messages transmitted by conventionalchannels.


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Quantum Key DistributionAlice communicates with Bob via a communication

channel sending him a photons.

Then they discuss results using public channel.

After getting an encryption key Bob can encrypt hismessages and send them by any public channel.


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APPLICATION OF QUANTUM

CRYPTOGRAPHYQuantum cryptography systems are used by some

government agencies, large banks,telecommunications companies and othercorporations who handle sensitive or military data.


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Commercial Quantum Cryptography Provider

Id Quantique, Geneva Switzerland

Optical fiber based systemTens of kilometers distances.

MagiQ Technologies, NY CityOptical fiber glass

Up to 100 kilometer distances


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NEC Tokyo, 150 kilometers

QinetiQ Famborough, EnglandThrough the air 10 kilometers

Supplied system to BBN in Cambridge Mass.


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Thank you

Quantum Crytography Ppt

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