1. The privacy in the era of
quantum computers
Dr. Nicolò Leone
nicolo.leone@unitn.it
21/03/23
NanoScience
Laboratory

2. Quantum
computers are
great!!!
Solve different kinds of
classically unsolvable problems.

3. Any
downside?
The title of the presentation has
spoiled it…

4. Based on Public key cryptography system
Sharing of information

5. Based on
assumption
The considered problem is
hard to be solved by
classical computers
Public key
cryptography Public
Private
Connected by the
algorithm
Es: the public key =
product of the two
prime numbers
Alice Bob
Alice

6. Based on
assumption
The considered problem is
hard to be solved by
classical computers
Public key
cryptography
Encrypted with Alice Public key
Alice Bob

7. Based on
assumption
The considered problem is
hard to be solved by
classical computers
Public key
cryptography Alice decrypts the message using his private key.
Factorisation of large prime numbers.
Solved in exponential time
Alice Bob

8. Quantum
computing

9. Solve factorisation
problems
Quantum
Computers
Can solve other
crypto. problems?
Algorithm
Only a few
Future
Not enough qubit
Time
Polynomial
Security
Cannot simply take a
longer key
https://newsroom.ibm.com/media-quantum-innovation?keywords=quantum&l=100

10. Time is
passing.
The company are approaching the
number of necessary qubits.
https://newsroom.ibm.com/media-quantum-innovation?keywords=quantum&l=100

11. Post-quantum cryptography
Find problems that are still difficult to be
solved by quantum computers
Quantum cryptography
Using quantum physics to beat quantum
physics.

12. PRO
Post-quantum
cryptography
CONS
Security
Assumptions
Demanding
Dedicated hardware
Deployment
Software
Cost
Cheap

13. PRO
Quantum cryptography
Quantum key distribution
CONS
Deployment
Hardware
Cost
Expensive
Security
Quantum mechanics
Demanding
Dedicated hardware
https://www.qticompany.com/products/

14. BB84
First protocol proposed by
Bennett and Bressard in
1984
Quantum key
distribution
The key is not transmitted
Alice Bob

15. Quantum channel
Channel in which we inject
the quantum light
Quantum key
distribution
Alice Bob

16. Polarization
Direction of oscillation of
the electronic field
Quantum key
distribution
0 1
B1
B2
B1
B2
Alice Bob

17. Input randomness
It is necessary to randomly
select the base and the
digit to send
Quantum key
distribution
0 1
B1
B2
B1
B2
Alice Bob

18. Input randomness
Bob needs to select its
measurement basis also
randomly.
Quantum key
distribution
0 1
B1
B2
B1
B2
Alice Bob

19. Quantum collapse
Bob projects the
wavefunction of the
photon.
Quantum key
distribution
ℙ(V) = 1

20. Quantum collapse
Bob projects the
wavefunction of the
photon.
Quantum key
distribution
ℙ(V) = 1
ℙ(V) = 0.5
ℙ(H) = 0.5

21. Now let’s enter in
the protocol
Quantum key
distribution
#1 #2 #3 #4 #5 #6 #7 #8 #9 #10
Alice Base B1 B2 B1 B1 B2 B1 B1 B2 B2 B1
Alice Digit 0 1 1 0 0 1 0 1 1 0
Bob Base B1 B1 B1 B2 B1 B1 B2 B2 B2 B2
Bob Result 0 X 1 X X 1 X 1 1 X
Alice Bob

22. Now let’s enter in
the protocol
Quantum key
distribution
#1 #2 #3 #4 #5 #6 #7 #8 #9 #10
Alice Base B1 B2 B1 B1 B2 B1 B1 B2 B2 B1
Alice Digit 0 1 1 0 0 1 0 1 1 0
Bob Base B1 B1 B1 B2 B1 B1 B2 B2 B2 B2
Bob Result 0 X 1 X X 1 X 1 1 X
Alice Bob

23. Basis
announcement
They keep the runs in
which the basis are the
same.
Quantum key
distribution
Alice and Bob announce the basis
used.
Alice Bob

24. The key creation
Bob and Alice have
obtained the same key
Quantum key
distribution
#1 #2 #3 #4 #5 #6 #7 #8 #9 #10
Alice Base B1 B1 B1 B2 B2
Alice Digit 0 1 1 1 1
Bob Base B1 B1 B1 B2 B2
Bob Result 0 1 1 1 1
Alice Bob

25. The appearance of
Eve
Now an Eavesdropper
appears and try to steal
the key.
Quantum key
distribution
Alice Bob
Eve

26. The appearance of
Eve
Now an Eavesdropper
appears and try to steal
the key.
Quantum key
distribution
Alice Bob
Eve

27. Eve performs an
intercept and
resend attack
Eve chooses the right
base.
Quantum key
distribution

28. Eve performs an
intercept and
resend attack
Eve chooses the wrong
base. Eve introduces
errors in the sequence.
Quantum key
distribution

29. Eve action
Errors are introduced in
the sequence.
Quantum key
distribution
#1 #2 #3 #4 #5 #6 #7 #8 #9 #10
Alice Base B1 B2 B1 B1 B2 B1 B1 B2 B2 B1
Alice Digit 0 1 1 0 0 1 0 1 1 0
Bob Base B1 B1 B1 B2 B1 B1 B2 B2 B2 B2
Bob Result 1 X 1 X X 1 X 0 0 X
Alice Bob

30. Error estimation
Alice and Bob share a
piece of their key.
Quantum key
distribution
Error estimation, by comparing a
piece of the key.
Alice Bob

31. Error estimation
All the errors are treated
as due to Eve.
Quantum key
distribution
Errors < Threshold_value
Alice Bob

32. One-time pad
A method that is 100%
secure.
Quantum key
distribution Encrypted message
B = 01000010
01000010 +
01100001 =
00100011
Key = 01100001
#
00100011 +
01100001 =
01000010
Key = 01100001
# = 00100011
B
Alice Bob

33. One-time pad
Never reuse the same key!
Quantum key
distribution
V
V
From: http://www.cryptosmith.com/archives/70
=
=
=
V
V
From: http://www.cryptosmith.com/archives/70
=
=

34. Secure forever!
It is theoretically the most secure approach that can be
implemented.
The attacks are unfeasible
It is better to try to compromise Alice or Bob
Cost reduction
A As the research proceeds the cost of the QKD will
decrease
Quantum-key
distribution

35. Actually testing a new prototype of bidirectional QKD system
Now

36. Find out more SPEQK Team info@speqk.com

37. |ψ⟩ =
1
2
(|Thank⟩ + |you⟩)