Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

陳君翰 BB84 0718

1,186 views

Published on

Published in: Technology
  • Be the first to comment

  • Be the first to like this

陳君翰 BB84 0718

  1. 1. Quantum Cryptography:Public key distributionand coin tossing<br />Charles H.Bennett Gilles Brassard<br />International Conference on Computers, Systems & Signal Processing,1984<br />Speaker:陳君翰<br />Quantum Information Security Lab<br />Professor: Tzonelih Hwang<br />
  2. 2. Outline<br />Background<br />Introduction<br />BB84 Protocol<br />Conclusion<br />
  3. 3. Background<br />Quantum Cryptography: Public key Distribution<br />Charles H. Bennett, Gilles Brassard<br />International Conference on Computers, Systems & Signal Processing,1984<br />First Quantum key distribution protocol<br />
  4. 4. Introduction<br />Quantum cryptosystem:Base on property of quantum:1.The uncertainty of measurement2.Nocloning theory<br />
  5. 5. BB84 Protocol<br />Bit:0<br />Bit:1<br /><ul><li>Definition</li></ul>R Base<br />0 °<br />90 °<br />D Base<br />45 °<br />-45 °<br />Quantum channel: with the property of quantum.<br />Classical channel: authentic channel<br />
  6. 6. BB84 Protocol concept<br />QB(T)<br />B’<br />Alice<br />T’=<br />T=<br />B’=<br />B=<br />B’’=Correct bases of B’<br />Randomly choose half of B’’ to discuss with Alice<br />Bob<br />[P(B’’(1)),V(B’’(1))]………….[P(B’’(N/4)),V(B’’(N/4))]<br />Verify<br />ok or eavesdroppers exist<br />
  7. 7. Case 1:No eavesdroppers<br />1 0 1 0 1 1 1 1<br />D R D R D R D R<br />Alice<br />1 0 1 0 1 1 1 1D DDDR RRR1 2 3 4 5 6 7 8 <br />1 0 1 101 0 1D RD R D R D R1 2 3 4 5 6 7 8 <br />1 0 1 1 0 1 0 1D R D R D R D R1 2 3 4 5 6 7 8 <br />1 0 1 0 1 1 1 1D DDDR RRR1 2 3 4 5 6 7 8<br />1,3,6,8<br />Position 1,3,6,8 <br />are the same base<br />Randomly choose numbers to discuss with Alice<br />Bob<br />(6,1),(8,1)<br />ok<br />
  8. 8. Case 2:Have eavesdroppers<br />Assume use D base<br />1 0 1 0 1 1 1 1<br />D R D R D R D R<br />Alice<br />1 0 1 0 1 1 1 1D DDDR RRR1 2 3 4 5 6 7 8 <br />1 0 1 111 10D RD R D R D R1 2 3 4 5 6 7 8 <br />1 0 1 1 1 1 1 0D R D R D R D R1 2 3 4 5 6 7 8<br />1 0 1 0 1 1 1 1D DDDR RRR1 2 3 4 5 6 7 8<br />1 0 1 0 1 1 1 1D DDDR RRR1 2 3 4 5 6 7 8<br />1 0 1 1 1 1 1 0D R D R D R D R1 2 3 4 5 6 7 8<br />1,3,6,8<br />Bob<br />Eve<br />(6,1),(8,0)<br />Eavesdropper exist!<br />
  9. 9. Analysis BB84 Protocol<br />Probability of eavesdropper :<br />1 bit:<br />N bit:<br />When N ↑,it’s easier to detect eavesdroppers exist or not.<br />
  10. 10. Analysis BB84 Protocol Cont.<br />Qubit efficient:<br />N bits<br />B’<br />Alice<br />Correct bases of B’<br />(R,R) <br />(D,D) <br />(R,D)<br />(D,R)<br />N/2 bits<br />(R,R) <br />(D,D) <br />(R,D)<br />(D,R)<br />Discussion<br />Security/Not security<br />Bob<br />N/4 bits<br />to discuss<br />N/4 bits<br />as key<br />
  11. 11. Qubit efficiency:<br />Utilization is only 25%! <br />
  12. 12. Conclusion<br />Advantages:<br />Without exchanging information initially.<br />Eavesdroppers can be detected.<br />Disadvantages:<br />Low utilization<br />Photons may be lost in transmitting<br />
  13. 13. Thank you<br />

×