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An affordable Quantum Cryptography system
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Transcript of An affordable Quantum Cryptography system
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
Some cities (Durban, Madrid, London) are going to be completely cabled to apply quantum cryptography
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 for 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 randomly 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.