Quantum encryption BB84

Transcript

1. Quantum Cryptography: Public key distribution and coin tossing Charles Bennett & Gilles Brassard International conference on Computers, Systems & Signal Processing Bangalore, India December 10-12, 1984
2. science -> tbhfodd physics -> qgxtjdr micro-photoluminescence? one-time-pad: 1 0 0 1 1 1 0
3. transmission probability: absorption probability: Polarised photons: Vertical Horizontal 45 degree cos2 ( a - b ) sin2 ( a - b )
4. How does it work? Bob Alice 1001010 1101001 RDDRD RDRRR Rectilinear basis: 0o : binary 0 90o : binary 1 Diagonal basis: 45o : binary 0 135o : binary 1 45,90,13 5,0.... Bob's filters DRDDR RDRDR 1 001 0 100 1 011 Bob's bits Alice's bits Alice's bases encoded photons
5. 0 1 1 0 1 1 0 0 1 0 1 1 0 0 1 D R D R R R R R D D R D D D R R D D R R D D R D R D D D D R 1 1 1 0 0 0 1 1 1 0 1 R D R D D R R D D D R Ok Ok Ok Ok Ok OK 1 1 1 0 0 1 Alice's Bits Alice's Bases Alice's Photons Bob's Bases Bob's Bits Bob's announces bases of received bits Random reveal: Resulting one-time-pad:
6. Why is it secure? No passive eavesdropping: you cannot split a photon. All Bob's information carrying bits will agree with Alice's
7. Evil Eve the eavesdropper Bob Alice 45,90,135 ,0.... Bob's filters DRDDRR DRDR 1 0010 1001 011 Bob's bits encoded photons Eve RRRRRR RRRR 50/50 disagreement Eve's random filters Alice and Bob can check for eavesdropping by publicly comparing some random subset of the received photons
8. Coin tossing: 50/50 chance game between "distrustful" parties Alice chooses one basis, Bob must guess
9. 0 1 1 0 1 1 0 0 1 0 1 1 0 0 1 R R R R R R R R R R R R R R R R D D R R D D R D R D D D D R 0 1 0 0 1 1 0 1 1 0 1 1 0 1 1 0 0 1 0 1 1 0 0 1 Alice's Bits Alice's Bases Alice's Photons Bob's Bases Bob's R basis Bob's D basis
10. Single photons Why? Because Alice must know how many photons she is sending to Bob!
11. Quantum dots! Creates anti-bunched light. Test with autocorrelation measurement.
12. Perfect Real Simulated curves Hanbury-Brown Twiss Experiment