Uncrackable beams of light

Tue Sep 9 22:09:19 EDT 2003

<http://www.economist.com/science/tq/PrinterFriendly.cfm?Story_ID=2020013>

The Economist

MONITOR

Uncrackable beams of light
Sep 4th 2003
>From The Economist print edition

Quantum cryptography±hailed by theoreticians as the ultimate of uncrackable
codes±is finally going commercial

IN THE 1992 film 1Ž4Sneakers1Ž2, the ostensible research topic of one of
the main characters was something called 1Ž4setec astronomy1Ž2. This was an
anagram of the words 1Ž4too many secrets1Ž2. The research was supposed to
be about developing a method for decoding all existing encryption codes.
Well, if that were ever the case, it certainly isn't any more±thanks to a
start-up in Somerville, Massachusetts, called Magi Q.

Magi Qis in the final stages of testing a system for quantum cryptography,
which it plans to release commercially within the next few months.
Encryption engineers have long waxed lyrical about quantum cryptography,
but this is among the very first commercial implementations. The advantage
of quantum cryptography schemes is that the code they generate are simply
not±even in theory±breakable.

The scheme devised by Magi Q, called Navajo, does not use quantum effects
to transmit the secret data. Instead, it is the keys used to encrypt the
data that rely on quantum theory. If these keys are changed frequently (up
to 1,000 times a second in Navajo's case), the risk that an eavesdropper
without the key would be able to decrypt the data can be proved
mathematically to be zero. Of course, given the key, the task would become
a trivial one.

Navajo transmits the changing key sequence over a secure fibre-optic link
as a stream of polarised photons (indivisible particles of light). Because
the polarisation reflects the amount of electro-magnetic radiation allowed
to radiate at an angle to a light beam's direction, it can be considered to
be a measure of the angular dependence of the light.

Should an eavesdropper tap into the secure fibre-optic line, he would
disrupt this stream of polarised photons by the very act of observing
them±and the tampering could be instantly detected. By changing the key
frequently, Navajo could turn an off-the-shelf encryption scheme such as
AES (Advanced Encryption System) into something that was essentially
uncrackable.

As in all good encryption schemes, Navajo employs an element of redundancy.
The sender has two random-number generators. The first is used to generate
a random stream of zeros and ones±part of which will form the key. The
second random-number generator chooses which 1Ž4polarisation basis1Ž2 the
sender will use to transmit a given bit of the key. The sender uses two
different polarisation bases, which are at right-angles to one another.
Only by measuring in the correct polarisation basis can a receiver see
which bit was sent±otherwise the result is meaningless.

For each bit, the receiver arbitrarily chooses which polarisation basis to
use. The sender and receiver then talk over an open channel and find out
which bits they measured using the same basis. These bits (about half of
the total) then constitute the key. If someone has been eavesdropping, some
of these bits will have been disrupted. In that case the receiver will be
unable to decode the message, and will thus conclude that someone is
listening in.

This much is standard quantum cryptography. What is harder is building the
hardware that can do it quickly and cheaply enough to be commercially
viable. Magi Qis in a race with a Swiss company called ID Quantique to be
the first to do so, and currently appears to be in the lead.

Of course, if the quantum signal could be transmitted wirelessly, it would
liberate users from the cost and constraints of a fibre-optic line. Bob
Gelfond, Magi Q's founder and chief executive, is coy about the
possibility. He admits that his firm is working on the idea, but is not
saying anything at the moment.

For the time being, Navajo requires a dedicated fibre-optic link, which
only large corporations or governments are likely to have. And it currently
works only at distances of up to 50 kilometres. Any longer than that and
random interference degrades the stream of photons and makes them unusable.
But within these constraints, Navajo is fairly cheap. Magi Qplans to sell
it for $50,000 a set.

Given the glut of unused optical fibre buried beneath the streets of the
world, Magi Qis optimistic about Navajo's prospects. Andrew Hammond, a
vice-president at the company, reckons the market could potentially be
worth more than $1 billion a year, with much of the business coming from
firms with valuable intellectual property, such as drugmakers and aircraft
companies.

-- 
-----------------
R. A. Hettinga <mailto: rah at ibuc.com>
The Internet Bearer Underwriting Corporation <http://www.ibuc.com/>
44 Farquhar Street, Boston, MA 02131 USA
"... however it may deserve respect for its usefulness and antiquity,
[predicting the end of the world] has not been found agreeable to
experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire'

---------------------------------------------------------------------
The Cryptography Mailing List
Unsubscribe by sending "unsubscribe cryptography" to majordomo at metzdowd.com