Shyam MohanS4 – MCANO: 43College of Engineering,Trivandrum

OUTLINE• Basics of Cryptography• Basics of Quantum Computing• Need for Quantum Cryptography• Implementation of Quantum Cryptography• Quantum Key Distribution protocol BB84• BB84 with Eavesdropping• Research and Innovation• Conclusion• Interaction

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Basics of Cryptography• Cryptography is the coding and decoding of secret messages

• Cryptanalysis is the art of interpreting cipher text

• Key is only known to the sender and receiver

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Plain text like“Hello”

Cipher Text-.h7ib.v84%t9n

“Hello”ENCRYPTIONKEY KEY

DECRYPTION

Basics of Quantum Computing

• Quantum computers use quantum bits (QUBITS)• n bits can represent only one state from 2n possible states• n qubits can represent 2n quantum states simultaneously• A single qubit can represent 1 or 0 like a bit

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Need of Quantum Cryptography

• Bits in classical cryptography can be copied anonymously• Quantum computer can use Shor’s algorithm to break RSA encryptions• Commercial Quantum Computers by D-Wave • QuAIL (Quantum Artificial Intelligence Lab ) set up by NASA, Google, and

the Universities Space Research Association (USRA)• Unknown qubits cannot be accessed and copied like bits without changing

its values (Non-cloning quantum theorem)

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Implementation of Quantum Cryptography

• Implemented by using optical fiber cables which act as a quantum channel

• Or can be implemented aerially using laser and satellites

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Quantum Key Distribution protocol BB84

• BB84 - the security protocol for implementing Quantum Key Distribution(QKD)• It uses the idea of Photon polarization• Photons are used to represent single qubits (1,0)

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Steps in BB84 Protocol

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• Step 1 : Sender transmits a random sequence of 1’s and 0’s ( bits),which is converted into photon states by randomly using rectilinear and diagonal polarisation schemes .

• Step 2 : Receiver randomly interprets the photon states by randomly using his rectilinear and diagonal detectors

• Step 3 : Receiver sends information about sequence of detectors used randomly over a classical channel.

Steps in BB84 Protocol (contd..)

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• Step 4 : Sender in return tells the matching polarisation scheme guessed by receiver.

• Step 5 : Sender and receiver eliminates the unmatched interpretations and use the remaining binary equivalent as the key.

BB84 with Eavesdropping

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BB84 with Eavesdropping

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• Retained bit sequence (KEY) : 001110010100110• Confirms some randomly chosen bit values over classical channel like Internet or

telephone : 001110010100110

If no eavesdropping happened, the values will be same for both Alice and Bob. Then they drop the confirmed bits and uses the rest as

FINAL KEY: 01100101010Else if any mismatch occurs, eavesdropping is confirmed and current key generation is cancelled.

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Research and Developments• Tokyo Quantum Key Distribution Network deployed in October

2010

• Toshiba Quantum Key Distribution Network deployed exceeding 100 km in length

• Swiss Quantum Key Distribution Network in Geneva metropolitan area

• QC based voting machine developed by Id Quantique, is used in the Swiss canton of Geneva during the October 2007 parliamentary elections.

In a Nutshell• Quantum cryptography (or quantum key distribution) is a state-of-the-art

technique that exploits the properties of quantum mechanics to guarantee the secure exchange of secret keys.

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Interaction , Discussion , Analysis

What… ? Why? How ?

Who ?Can We…?

why can't ?Why not ?

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