19 April 2010, Cambridge, UK
• Cambridge team achieve new record bit rate for quantum key distribution
The Cambridge Lab of Toshiba Research Europe today announced a major breakthrough
that will allow ultra-secure encryption of sensitive data sent by banks, hospitals
and government organisations.
They have succeeded in demonstrating continuous operation of quantum key distribution
(QKD) with a secure bit rate exceeding 1 Megabit/sec over 50 km of fibre
for the first time. Averaged over a 24 hour period, this is 100–1000 times
higher than anything reported previously for a 50 km link. It was achieved
using two innovations developed by the Cambridge team: a novel light detector for
high bit rates and a feedback system which maintains a high bit rate at all times
and requires no manual set-up or adjustment. The results will be reported in the
scientific journal, Applied Physics Letters.
Significantly, the breakthrough will enable the everyday use of “one-time pad”
encryption, the only known method that is theoretically perfectly secret. Although
ultra-secure, the application of one-time pad encryption has been restricted in
the past as it requires the transmission of very long secret keys — the same
length as the data itself. For this reason it has only been used for short messages
in situations requiring very high security, for example by the military and security
services. Today's bit rate breakthrough will extend the application of this ultra-secure
communication method for everyday use.
Dr Andrew Shields, who directs this work at Toshiba Research Europe commented, “Although
the feasibility of QKD with megabits per second has been shown in the lab, these
experiments lasted only minutes or even seconds at a time and required manual adjustments.
To the best of our knowledge this is the first time that continuous operation has
been demonstrated at high bit rates. Although much development work remains this
advance could allow unconditionally secure communication with significant bandwidths.”
As an example of the new capability afforded by this system, these higher bit rates
would allow real time encryption of video using the one-time pad. This is now possible
due to the much higher and continuous bit rates that can be delivered with the new
technology. Previously it had been possible to encrypt continuous voice data, but
not video images.
Toshiba now plans to install a QKD technology demonstrator at the National Institute
of Information and Communications Technology (NICT) in Tokyo. Co-ordinator of the
Tokyo QKD Network, Dr. Masahide Sasaki, commented “The secure key rate
of 1 Megabit/sec over 50 km has been a milestone for mission critical
applications. The next challenge would be to put this level of technology into metropolitan
network operation. Our Japan-EU collaboration is going to do this within the next
few years.”
Toshiba will be presented as one of the Cambridge University Guild of Benefactors
on 19th April, in recognition of the collaboration between Toshiba Cambridge and
the Cavendish Laboratory of the University on next generation QKD technology.
For further press information, photography, or to request an interview, please contact:
Owen Waters or Elizabeth Chadwick
Nelson Bostock Communications +44 (0)20 7229 4400
elizabeth.chadwick/owen.waters@nelsonbostock.com
For further information about the work of Toshiba CRL, go to
http://www.toshiba-europe.com/research/crl/.
About the field demonstration at the Tokyo QKD Network, go to the conference web
page; http://www.uqcc2010.org/.
TECHNICAL BACKGROUND
Cryptography, the science of information security, is essential to protect electronic
business communication and e-commerce, enabling, for example, confidentiality, identification
of users and validation of transactions. All of these applications rely upon digital
keys, which are shared between the legitimate users, but must be kept secret from
everyone else. Maintaining the ability to distribute keys securely is thus one of
the most important battlefields in the cryptography arms race. It is essential to
be able to distribute keys between users securely. Furthermore, in order to protect
the system from crypto-analysis or key theft it is important to change the keys
frequently.
Quantum Key Distribution (QKD) is an automated method for distributing secret keys
across an optical fibre. A unique feature of QKD is that its security is derived
from the fundamental laws of Quantum Physics and does not therefore rely upon assumptions
about the computing power of an eavesdropper. An added benefit is that the keys
distributed by QKD will be secure in the future as well as today.
QKD is based upon sending encoding single photons (particles of light) along the
fibre. The laws of Quantum Physics dictate that any attempt by an eavesdropper to
intercept and measure the photons alters their encoding. This means that eavesdropping
on quantum keys can be detected.
The Toshiba QKD system is based on one-way optical propagation and the BB84 protocol
using decoy pulses. This protocol has been proven to be unconditionally secure,
ie satisfying the most stringent security criterion.
Current QKD systems are limited by the semiconductor devices (avalanche photodiodes)
used to detect the single photons. One photon triggers an avalanche of millions
of electrons in this semiconductor device which can be sensed by electrical circuitry
in the QKD system. The problem in present systems is that some of these avalanche
electrons can be trapped in the device and later stimulate a second spurious detection
count. As these noise counts cause errors in the key, current detectors must be
operated with long dead times to allow the decay of any trapped electrons. This
has limited the clock rate of current QKD systems to around 10 MHz and thus
the average secure key bit rate to a few kbit/sec for a 50 km fibre. The Toshiba
team has devised a method to detect much weaker avalanches. This strongly reduces
the chance for an electron to be trapped, allowing the detector to be operated at
much faster rates beyond 2 GHz. As the detector is based on a compact and rugged
semiconductor device, it is suitable for real-world applications.
For further information about the work of the Quantum Information Group at Toshiba
Cambridge, go to http://www.quantum.toshiba.co.uk/
About Toshiba
Toshiba is a world leader and innovator in pioneering high technology, a diversified
manufacturer and marketer of advanced electronic and electrical products spanning
information & communications equipment and systems; digital consumer products; electronic
devices and components; power systems, including nuclear energy; industrial and
social infrastructure systems; and home appliances.
Toshiba was founded in 1875, and today operates a global network of more than 740
companies, with 198,000 employees worldwide and annual sales surpassing US$76 billion.
Visit Toshiba's web site at www.toshiba.co.jp/index.htm
About Toshiba Research Europe Ltd
Toshiba Corporation is fully committed to the research and development of future
technologies. This commitment has resulted in Toshiba having a record number of
world firsts, including the first laptop PC (1985), the first single chip MPEG4
videophone LSI (1998) and the first DVD player (Oct. 1996). Over the 3 years to
end March 2010, the Corporation anticipates a total global R&D expenditure of JPY1,290bn.
Toshiba Corporation established its first overseas research centre in 1991, with
the opening of Toshiba Cambridge Research Centre Ltd in the UK. This was renamed
Toshiba Research Europe Ltd (TREL) in August 1998, when a new telecommunications
laboratory in Bristol was launched. TREL now has two research laboratories in the
UK; the Cambridge Research Laboratory (CRL) in Cambridge, and Telecommunications
Research Laboratory (TRL) in Bristol.
Associated publication:
A. R. Dixon et al., Applied Physics Letters, 96, 161102 (2010)
Download preprint [preprint is open access]
