Quantum cryptography is a way to share secret
digital keys
A system that allows
electronic messages to be sent with complete secrecy could be on the
verge of expanding beyond niche applications.
A team of British scientists has discovered a way to build
communications networks with quantum cryptography at a larger scale
than ever before.
Quantum cryptography has the potential to transform the way
sensitive data is protected.
Details appear in
Nature journal.
The system is based on a communication system, where information
is carried by individual photons - single particles of light.
Once these single photons of light are observed, they change.
That is, they cannot be intercepted by an "eavesdropper" without
leaving a detectable trace.
Quantum key distribution
- QKD is a method to share secret digital keys - random
combinations of 0s and 1s - securely on a communication network
- Those keys can then be used to encrypt or authenticate data
to stop other people reading or altering it
- Once two parties have swapped a key that they know to be
safe they can be sure that the messages they are sending each
other are secure
Secret communication
Until now, implementing a quantum
cryptography network had required a new fibre and an elaborate
photon detector for each additional user that was added to the
network, at considerable expense.
The team says they have now extended the way to send uncrackable
codes - referred to as "quantum key distribution" (QKD) - beyond
very niche applications.
Andrew Shields of Toshiba's Cambridge Research Laboratory and
colleagues, have demonstrated that up to 64 users can share a fibre
link and detector.
The network works on standard fibres that allows information from
multiple users to be combined and transmitted on a single fibre.
Encoding information on individual photons of light has the
"unique virtue that it allows the secrecy of the communication to be
tested", said Dr Shields.
"Now we can connect multiple users up to one single fibre and
allow them to share a connection to a quantum network.
"The advantage of that is we can now build quantum networks with
many more users than has been possible in the past, which also
reduces the cost per user," he told BBC News.
Existing optic fibres can be used to
carry quantum codes
The team said their work could make QKD more practical and was
now closer to being a widespread technology that could be used by
businesses, banks and government organisations.
Mobile cryptography
Hannes Huebel of Stockholm University, Sweden, said the new work
was a breakthrough finding that demonstrated that QKD could soon be
used more widely.
He said in the next decade people could even have a laser in
their smartphones which would allow them to send encrypted
information to others.
This is already one step closer to happening as
this week a team from the
University of Bristol, say they have developed a way of sending
secret quantum messages on handheld devices.
The team, writing in a paper published on Arxiv.org, report:
"This opens the way for quantum enhanced secure communications
between companies and members of the general public equipped with
handheld mobile devices, via telecom-fibre tethering."
Dr Huevel explained that at the moment the technology was still
mainly lab-based with highly specialised people operating the
technology.
"The aim is to go away from this to make it much user friendly
and cheaper. This new research is one step closer, it's the last
step between the end user and a proper network," Dr Huebel added.
'Middleman attacks'
Some however disagree that total security can be achieved with
quantum cryptography.
Karl Svozil, a theoretical physicist at the Vienna University of
Technology, Austria, said the protocol used in the current work was
not secure against all eavesdropping methods and required that the
classical channel must be uncompromised for quantum cryptography to
work.
If there were active "middleman attacks", there could be "active
eavesdropping", he said.
"The condition of quantum cryptography relies on certain rules
that need to be obeyed - only then is it unconditionally safe. The
newly proposed protocol is 'breakable' by middlemen attacks."
The quantum access network
- Each bit of the secret key is encoded on a single
particle of light (photon)
- Quantum theory dictates that single photons cannot be
intercepted without changing their encoding, this means an
eavesdropper will always leave a trace
- The signals from multiple users can be combined and
transmitted on a single fibre
- The receiver can be used to form a secret key with each
transmitter
- Can detect up to one billion photons per second allowing
up to 64 users on one link
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