Presented By, Mohammad Anees SSE, Mukka

Contents Cryptography Photon Polarization Quantum Key Distribution BB84 Protocol Security of Quantum Cryptography Milestones Applications Advantages Disadvantages Conclusion References

Introduction Cryptography Transmitting information with access restricted to the intended recipient even if the message is intercepted by others. Quantum An indivisible elementary particle, usually a photon. Quantum Cryptography The use of quantum mechanics to guarantee secure communication.

Cryptography Two types of Cryptography Symmetric / Private Key Asymmetric / Public Key Two types of Encryption Transposition Substitution

Photon Polarization

Quantum Key Distribution BB84 protocol Charles H. Bennett and Gilles Brassard (1984) Alice sends Bob a string of encoded photons. Bob measures the string of encoded photons using random basis (rectilinear or diagonal). Alice and Bob publically compare the basis they encoded and measured in, and discard all results where they do not match. The result is the Shared Secret Key.

Channels

Sender-receiver of photons Suppose Alice uses 0 deg/90 deg polarizer sending photons to Bob. But she does not reveal which. Bob can determine photons by using filter aligned to the same basis. But if he uses 45 deg/135 deg polarizer to measure the photon he will not be able to determine any information about the initial polarization of the photon. The result of his measurement will be completely random.

Eavesdropper Eve If Eve uses the filter aligned with Alice’s she can recover the original polarization of the photon. If she uses the misaligned filter she will receive no information about the photon. Also she will influence the original photon and be unable to retransmit it with the original polarization. Bob will be able to deduce Eve’s presence.

Example of key distribution

Security of quantum key distribution Quantum cryptography obtains its fundamental security from the fact that each qubit is carried by a single photon, and each photon will be altered as soon as it is read. This makes impossible to intercept message without being detected.

Milestones World's first bank transfer using quantum cryptography in Vienna, Austria DARPA Quantum Cryptographic Network in Massachusetts, USA. Mar BB84 implementation along km fibre optic cable in Canary Islands. Oct Quantum Cryptography used in Geneva for Swiss elections. Oct World's first computer network protected by quantum cryptography implemented in Vienna Japanese researchers succeed in quantum cryptographic key distribution from single-photon emitter at 50 km

Applications Cryptography is of increasing importance in our technological age using : broadcast network communications Internet Banking cell phones which may transmit sensitive information related to finances, politics, business and private confidential matters.

ADVANTAGES Based on natural quantum laws Perfect for public communication Easy to detect an eavesdropper Security provided by QKD is future proofed

DISADVANTAGES Practical systems are limited by distance Photon emitters and detectors are far from perfect, causing errors Detecting eavesdropper in the presence of noise is difficult.

Conclusion Quantum cryptography is a major achievement in security engineering.

References Ekert, A What is quantum cryptography. Ford, J. Quantum cryptography tutorial. Wikipedia Quantum Key Distribution Protocols and Applications – Sheila Cobourne

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