Rita Pizzi

Department of Information TechnologyUniversità degli Studi di Milano

Rita Pizzi

Department of Information TechnologyUniversità degli Studi di Milano

PROTOTYPE OF A QUANTUM

CRYPTOGRAPHY SYSTEM FOR THE END USER

QUANTUM INFORMATIONQUANTUM INFORMATION

The quantum computer does non exist yetBut a real world application based on quantum

information exists:QUANTUM CRYPTOGRAPHY

It allows the secure transmission of data, independent from algorithms and computing power of the attacker

It is possible to detect any intrusion immediately

Nowadays optical fiber systems exist that reach distances of 100 km

Methods to increase distances and usability are underway (quantum repeaters for optical fibers / satellite

transmissions)

QUANTUM CRYPTOGRAPHY TODAYQUANTUM CRYPTOGRAPHY TODAY

Quantum cryptography performances captured the interest of banks, big companies and institutions.

Systems already on sale: • MagiQ Technologies New York • idQuantique Geneve• SmartQuantum York

• QinetiQ UK (defence)• Toshiba Corp Tokio • National Institute of Standards and

Technology (US government agency )

are acquiring this technology

QUANTUM CRYPTOGRAPHY TODAY QUANTUM CRYPTOGRAPHY TODAY

Today the cost of a system is around 100.000 $

Less expensive applications are interesting, affordable for the end user:

ATM terminals, online internet transactions

We developed our prototype to this purpose

A compact and cheap system that could be embedded in a smartphone

THE BB84 PROTOCOL(Bennet Brassard 1984)THE BB84 PROTOCOL(Bennet Brassard 1984)

In quantum physics the act of observation modifies in an

unpredictable way the observed system

Thus any external action in the system will corrupt the flow of information,

revealing the intrusion

The BB84 protocol is based on the polarization properties of the photons

THE BB84 PROTOCOL (Bennet Brassard 1984)

THE BB84 PROTOCOL (Bennet Brassard 1984)

Alice chooses rendomly a sequence of 1 and 0 bits, turns them into photons, applies to each bit

one of the possible polarizations, then sends them to Bob.

Bob chooses randomly a polarization to examine each of the received photons, turns them into bits

and records the results of his observations.

THE BB84 PROTOCOL (Bennet Brassard 1984)

THE BB84 PROTOCOL (Bennet Brassard 1984)

Now Bob sends to Alice on a public channel (e.g. Internet) his polarization sequence (but NOT the

result of his measures)

Alice selects the positions in the sequence that Bob sent correctly and sends them back to Bob on

the public channel

THE BB84 PROTOCOL (Bennet Brassard 1984)

THE BB84 PROTOCOL (Bennet Brassard 1984)

Both Alice and Bob share now an identical sequence of bits, i.e. they possess a shared key

that is definitely secret.

BB84 – THE INTRUSIONBB84 – THE INTRUSION

In this kind of transaction an intrinsic error rate exists, that can be minimized by means of error correction and

privacy amplification techniques

If an eardropper E interposes to intercept the sequence of bits, for the quantum physics laws he corrupts the sequence and sends back to Bob a sequence with a

much higher error rate

This reveals immediately the presence of the intruder and the transaction can be stopped without damage

OUR SYSTEMOUR SYSTEMOur system is based on two

custom cards: the transmitter and the receiver.

TRANSMITTERIt is an electronic circuit that

drives four high-performances LEDs

The LEDS are endowed with polarizing filters and their

intensity is suitably attenuated.

Random logical signals are generated that turn on the

four LEDs in sequence

OUR SYSTEMOUR SYSTEMRECEIVER

The receiving circuit must re-establish a sequence of data

starting from the received photons.

Four high-sensitivity photodiodes turn the photons

(passed through four polarizing filters) into

electrical signals, then into bits.

This is made possible by a logic state analyzer that

detects the voltage peaks coming from the

photodiodes.

THE FIRMWARETHE FIRMWARE

A C-written software drives the whole process on two separated PCs.

In the first PC the software, using the BlumBlumShub pseudorandom number generator, generates the sequence of bits and synchronizes it

This is acquired by the transmitter through the parallel port.

THE FIRMWARETHE FIRMWARE

On the second PC the software reads the signals reconstructed by the logic state

analyzer and syncronizes them

We also simulated the comparison on public channel between sequences generated by

transmitter and receiver

At the end of simulation we obtain the secure key.

FUTURE DEVELOPMENTSFUTURE DEVELOPMENTS

At the moment our system is a prototype on optical bench

In the future it can be adapted to work on optical fibers or directly on ATM terminals.

The system performances are improvablewith more effective components and with

more powerful software algorithms

FUTURE DEVELOPMENTSFUTURE DEVELOPMENTS

We are acquiring avalanche photodiodes that will ensure single-photon performances

The software random number generator will be substituted by a portable and

affordable hardware generator (IdQuantique o custom)

Robust algorithms of error correction and privacy amplification will be developed.