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Case Studies - Information, Communication and Electronics

Quantum Cryptography

Where we came in
A completely secure global data transmission network has long been a goal for governments and commercial organisations alike. Research and development work by QinetiQ's quantum cryptography experts and a team from Ludwig Maximillians University in Germany has put made that goal a step closer.

What we did
The two teams have been working on an unbreakable digital key using photons. The system is not designed to send messages, but rather to establish identical random numbers at the transmission and reception sites.

The security of the system lies in the fact that photons are quantum particles and therefore cannot be divided. Each encoded photon can, for all practical purposes, be received only by one individual receptor site. Anyone trying to covertly monitor the transmitted signal sets up disruption to some of the photons in the pulsed sequence that travels from transmitter to receiver. So their attempts at monitoring are always detectable.

We developed the process in which:


  • single photons are first polarised to transform them into binary 'bits'
  • a random sequence of these bits is then transmitted to the receiver
  • the received bits are used to build a large random number.


In theory, the received sequence should be identical to the one sent, but in reality there are unavoidable transmission losses. So the system relies on matching sent bits to received bits by cross-referencing the time of arrival and the time of transmission.

The receiver sends the transmitter the time the received pulses arrive, by phone or another conventional data link. This allows the sender to erase any bits in the sequence that were lost in transmission, and thus create two matching sequences.

A separate randomisation factor, via polarisation rotation of the pulses, guarantees absolute security of the transmission. So the sender and receiver end up with the same randomly-generated number, or cryptographic key. This is the basis for the encryption method that encodes data before transmission, and decodes it at the receiving site.
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The security of this communication method is guaranteed, as photons, being quantum particles, are indivisible The security of this communication method is guaranteed, as photons, being quantum particles, are indivisible.
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The results and benefits
The QinetiQ and Ludwig Maximillians University teams have successfully carried out an experiment by transmitting a digital key for deciphering coded information between two mountain tops in Germany - a distance of more than 23km.

Their success has validated the work done on our key-exchange encryption system. Such a system would be able to encode and decode data transmissions sent between orbiting satellites and earth-based ground stations.

A working global system would play a fundamental part in a transmission network for government-to-government, military and commercially-sensitive communications that is completely safe from the attentions of covert eavesdroppers.

Anything is possible - just ask
This is a prime example of how we are applying our knowledge and technological expertise to projects of global significance, to find solutions to problems.

We could do the same for you. Whatever your requirements or problems, we have the ideas, know how and solutions.
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