The document outlines the basics of quantum cryptography including: - The need for quantum cryptography due to limitations of classical cryptography in the face of quantum computers. - The BB84 quantum key distribution protocol which uses photon polarization to randomly generate and distribute encryption keys between two parties in a way that can detect eavesdropping. - How the BB84 protocol works including key generation and verification steps to detect if the transmitted quantum states were accessed or copied without authorization during transmission. - Examples of real-world deployments of quantum cryptography networks to securely distribute keys for applications such as voting machines.

1. Shyam Mohan
S4 – MCA
NO: 43
College of Engineering,
Trivandrum

2. 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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3. 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”
ENCRYPTION
KEY KEY
DECRYPTION

4. 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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5. 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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6. 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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7. 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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8. 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.

9. 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.

10. BB84 with Eavesdropping
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11. 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: 01100101010
Else 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.

13. 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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14. Interaction , Discussion , Analysis
What… ?
Why? How ?
Who ?
Can We…?
why can't ?
Why not ?

16. ALL