Quantum Key Distribution (QKD) Prashanta Kharel Applied Physics - PowerPoint PPT Presentation

Quantum Key Distribution (QKD) Prashanta Kharel Applied Physics Seminar November 2012 Friday, December 7, 12

Friday, December 7, 12

Messag Classical Key Distribution RSA Encryption Message: “SEAS” “01000101” e d • Relies on two distinct large prime numbers • factorization of prime • exponential problem Private Key Public Key • limited only by ! = ! ! ! ( mod ! n ) ! = ! ! ! ( mod ! n ) computational power Encode Decode “01000101” “SEAS” Friday, December 7, 12

M Quantum Key Distribution(QKD) Classical Channel • relies on fundamental quantum mechanics • unconditionally secure Bob Alice • eavesdropper can be Quantum Channel detected Eve Friday, December 7, 12

Messag BB84-Protocol RSA Encryption V- Polarized • Uses polarized light H-Polarized • Uncertainty principle for Calcite Crystal single photons Measure Measure V P = 1/2 d D H P=1/2 Diagonal Basis Rectilinear Basis Friday, December 7, 12

Messag BB84-Protocol How to share a H/V Basis D/d Basis H=0 D=0 secret key? V=1 d=1 0 1 1 0 1 1 0 0 1 0 1 Bits D R D R R R R D R D D Alice’s Random Basis Quantum Photon Alice Sends Channel D D R R R R D D R R D Bob’s Random Basis 0 0 1 0 1 1 0 1 1 Bits received by Bob D D R R R D D R D Bob Report Basis Alice confirms correct ones OK OK OK OK OK OK Public Channel 0 0 1 0 1 1 Shifted Key Correlated measurements Friday, December 7, 12

Messag Ekert’s Protocol Three Conjugate Basis: H/V, D/d, L/R Alice Random Photon Source Random Bob • Shifted key is smaller • More sensitive to eavesdropping Friday, December 7, 12

Messag Conclusion • 2009 Yamamoto, up to 105 km, 17 kbits/sec • 2012 Shields, up to 90 km, ~1Gbits/sec Future: • High Key Generation Rate • Noisy channel • QKD over longer distances Friday, December 7, 12

Messag Questions Friday, December 7, 12

Messag Sources • C. H. Bennett and G. Brassard, “Quantum cryptography: Public-key distribution and coin tossing,” in Proceedings of IEEE International Conference on Computers, Systems and Signal Processing, Bangalore, India, 1984, (IEEE Press, 1984), pp. 175–179; C.H. Bennett and G. Brassard, “Quantum public key distribution,” IBM Technical Disclosure Bulletin 28, 3153–3163 (1985). • N. Ilic, “The Ekert Protocol”, University of Waterloo • Y. Yamamoto et al., “Quantum key distribution over 40 dB channel loss using superconducting single photon detectors,” arXiv, 2009 • Zeeya Merali, “Quantum cryptography conquers noise problem,” Nature, 2012 Friday, December 7, 12