Toshiba creates hack-proof system

Computer hacking could become a thing of the past with an advance in nano-engineered LED technology, its developers claimed this week.

Toshiba Research Europe said its LED, which emits just one photon of light at a time, can offer electronic encryption that is impossible to break. When the LED was first revealed last year, it could work at only low frequencies, so only a small quantity of encoded information could be transmitted at a time. Recent work means it can now transmit at 200MHz, and it will soon be taken up to gigahertz levels, making the technology a viable encryption tool.

However clever the hacker is, the system would be 100 per cent secure, claimed Toshiba researcher Dr Andrew Shields. He said his method is ‘the first electrically driven single-photon source’.

Electronic transactions generally exploit cryptographic methods to encode data according to a unique ‘key’, which each legitimate user must have. If this key is intercepted, a criminal can muscle in. But by encoding data as the polarisation or phase of single photons – quantum cryptography – cryptographers can produce an ‘unhackable’ code.

Unlike a normal signal, photons tapped off by a hacker will not be received at the other end, alerting genuine users to the presence of an intruder. Nor can a hacker retransmit the photons once tapped since they are disturbed by measurement and will ‘read’ differently at the other end.

The increase in capability means that the system can transmit crypto keys complex enough to be uncrackable in themselves, whereas before it could only have carried simple keys.

Developed in conjunction with the University of Cambridge, the LED uses an indium arsenide ‘quantum dot’ semiconductor embedded in a gallium arsenide structure. At 15nm wide and 5nm high, the dot is so small that a maximum of two photons can pass through at a time when current is applied.

As they have different wavelengths, one of the photons can be blocked with a filter, though the engineers can generally control the current pulses to make just one at a time.

The latest version of the LED exploits the combination of negatively charged electrons and what quantum physicists call ‘holes’. These are positively charged ‘particles’ in the quantum dot semiconductor (technically the absence of an electron).

Applying pulses of current to the quantum dot makes it emit one or two pairs of electrons and ‘holes’ that recombine to emit photons.

The speed at which these particles combine defines the frequency at which the photons can be emitted. The successful test at 200MHz has given the researchers the confidence to go ahead with higher frequency tests involving setting the quantum dot in an optical cavity.

An optical cavity consists of facing mirrors that further aid photon recombination by bouncing particles around a confined space. Shields says the technology could be viable in three years.

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