The adventures of Alice, Bob & Eve in the Quantumland

1. The adventures of Alice, Bob & Eve in the Quantumland Stefano Mancini University of Camerino, Italy

2. Outline (part 3) • Security of BB84 against symmetric individual attacks • Other QKD protocols and their security • The ultimate security proof

3. The problem of security • Show that exists a nonzero (positive) bound for tolerable QBER • Such a bound should come from the conditions of KC’s theorem H(a:b)>H(a:e) or H(a:b)>H(b:e)

4. Symmetric Individual Attacks A B qubit U probe E E

5. Security against symmetric individual attacks

6. F

7. ˜ ˜ ˜ ˜ ˜ ˜ ˜ ˜

9. Security conditions

10. B92 protocol

11. b=1 implies perfect anticorrelations b’ # usable bits _____________________________ R= (# transmitted qubits)+(# transmitted bits) R= 1/8

12. E91 protocol

13. a’ b a’=b’ implies perfect correlations # usable bits _____________________________ R= (# transmitted qubits)+(# transmitted bits) R= 1/6

14. Security of E91 protocol | | Equivalence between E91 & BB84

15. The ultimate security proof

17. Experimental Quantum Cryptography • First demonstration on a table at IBM labs over a distance of 30 cm (1989) • Experiments with fibres (over a distance of 30-50 Km, 1996-2004) using faint laser pulses or entangled photons • Experiments in free space (over a distance of few Km) • Quantum Cryptography Devices already available in the market!