http://www.computerworld.com/printthis/2004/0,4814,96111,00.html
- Computerworld
Quantum cryptography gets practical
Opinion by Bob Gelfond, MagiQ Technologies Inc.
SEPTEMBER 30, 2004 (COMPUTERWORLD) - In theory and in labs, quantum
cryptography -- cryptography based on the laws of physics rather than
traditional, computational difficulty -- has been around for years.
Advancements in science and in the world's telecommunications
infrastructure, however, have led to the commercialization of this
technology and its practical application in industries where high-value
assets must be secure.
Protecting information today usually involves the use of a cryptographic
protocol where sensitive information is encrypted into a form that would be
unreadable by anyone without a key. For this system to work effectively,
the key must be absolutely random and kept secret from everyone except the
communicating parties. It must also be refreshed regularly to keep the
communications channel safe. The challenge resides in the techniques used
for the encryption and distribution of this key to its intended parties to
avoid any interception of the key or any eavesdropping by a third party.
Many organizations are advancing quantum technology and bringing it
outside academia. Research labs, private companies, international alliances
such as the European Union and agencies such as the Defense Advanced
Research Projects Agency are investing tens of millions of dollars in
quantum research, with projects specifically focused on the challenge of
key distribution.
The trouble with key distribution
Huge investment in the late 1990s through 2001 created a vast
telecommunications infrastructure resulting in millions of miles of optical
fiber laid across the country and throughout buildings to enable high-speed
communications. This revolution combined a heavy reliance on fiber-optic
infrastructure with the use of open network protocols such as Ethernet and
IP to help systems communicate.
Although this investment delivers increased productivity, dependence on
optical fiber compounds key distribution challenges because of the relative
ease with which optical taps can be used. With thousands of photons
representing each bit of data traveling over fiber, nonintrusive, low-cost
optical taps placed anywhere along the fiber can siphon off enough data
without degrading the signal to cause a security breach. The threat profile
is particularly high where clusters of telecommunications gear are found in
closets, the basements of parking garages or central offices. Data can be
tapped through monitoring jacks on this equipment with inexpensive handheld
devices. This enables data to be compromised without eavesdroppers
disclosing themselves to the communicating parties.
Another important aspect of this problem is the refresh rate of the keys.
Taking large systems off-line to refresh keys can cause considerable
headaches, such as halting business operations and creating other security
threats. Therefore, many traditional key-distribution systems refresh keys
less than once per year. Infrequent key refreshing is detrimental to the
security of a system because it makes brute-force attacks much easier and
can thereby provide an eavesdropper with full access to encrypted
information until the compromised key is refreshed.
Adding quantum physics to the key distribution equation
Companies are now in a position to use advancements in quantum
cryptography, such as quantum key distribution (QKD) systems, to secure
their most valued information. Two factors have made this possible: the
vast stretches of optical fiber (lit and dark) laid in metropolitan areas,
and the decreasing cost in recent years of components necessary for
producing QKD systems as a result of the over-investment in
telecommunications during the early 2000s.
Based on the laws of quantum mechanics, the keys generated and
disseminated using QKD systems have proved to be absolutely random and
secure. Keys are encoded on a photon-by-photon basis, and quantum mechanics
guarantees that the act of an eavesdropper intercepting a photon will
irretrievably change the information encoded on that photon. Therefore, the
eavesdropper can't copy or read the photon -- or the information encoded on
it -- without modifying it, which makes it possible to detect the security
breach. In addition to mitigating the threat of optical taps, QKD systems
are able to refresh keys at a rate of up to 10 times per second, further
increasing the level of security of the encrypted data.
Not for everyone
Quantum key distribution systems aren't intended for everyday use: You
won't find a QKD system in the home office anytime soon. One reason is that
a QKD system requires a dedicated fiber-optic line. Also, because the loss
of photons over longer distances, these systems have current distance
limitations of approximately 120 kilometers (nearly 75 miles) which is
common with optical
