Stefano Mancini

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
  KCs theorem
• H(ab)gtH(ae) or H(ab)gtH(be)

4
Symmetric Individual Attacks
A
B
qubit
U
probe
E
E
5
Security against symmetric individual attacks
6
F
7








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Security conditions
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B92 protocol
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b1 implies perfect anticorrelations
b

usable bits

_____________________________
R
( transmitted qubits)( transmitted bits)

R 1/8

12
E91 protocol
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b
a
ab implies perfect correlations




usable bits
_____________________________
R
( transmitted qubits)( transmitted bits)
R 1/6




14
Security of E91 protocol


Equivalence between E91 BB84
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The ultimate security proof
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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!