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Quantum Encryption
Cryptography’s Holy Grail
by Samantha Matthews
Conventional Encryption
 Data transmission is asynchronous.
 Data are sent in groups of photons and
translated by the receiving computer.
 The encryption key is sent embedded in
the data stream and can be intercepted in
transit without either party’s knowledge.
Quantum Encryption
 Data transmission is synchronous.
 Data are sent in weak pulses of photons.
 The physical behavior of the particles
themselves gives the receiver the encryption
key.
 If a third party interrupts the data stream, the
encryption key is rendered useless and both
parties are alerted.
 The encryption key isn’t in the message, it is
the message.
Why Quantum Encryption Works
 Subatomic particles can exist in multiple
states until something interacts with
them and changes those states.
 Heisenberg’s Uncertainty Principle
px1/2*h/2
We can know the location or linear
momentum of a particle, but not both.
 Think of Schrödinger's cat, a quantum
mechanical outgrowth of this principle.
Why Quantum Encryption Works,
Part 2
 It makes use of quantum entanglement,
the interdependency of the physical
states of quantum particles.
 Changing the state of one particle
(through observation) changes the state
of other particles around it.
How Quantum Encryption Works
on the Sender’s End
 A laser separates individual photons and sends them
to an instrument called a modulator.
 The modulator sends the photons to other network
nodes via fiber-optic cable.
 The photons are encoded by sending them at different
time intervals.
Chip Elliot, an engineer for BBN Technologies, next to a quantum cryptograph.
How Quantum Encryption Works
on the Receiver’s End
 The receiver accepts the photons and examines their
modulation. If it matches the original one, the
encryption key is saved and used to decode data sent
over the network through conventional methods, such
as the Internet.
Martin Jasper of Boston University examines a single photon detector module.
Why Quantum Encryption Is
Needed
 Many researchers are currently trying to
develop quantum computers, which are
believed to be capable of exponentially
greater computing power than today’s
supercomputers.
 If quantum computers become a reality
before quantum encryption does,
modern encryption methods could
become obsolete.
Applications of Quantum
Encryption
 Governmental and intelligence
operations
 Financial and business transactions
 Personal encryption (files, e-mail)
 Many things no one’s thought of yet
More Information
 I found these websites useful.
 http://www.cs.caltech.edu/~westside/quantumintro.html
 http://www.qubit.org/library/intros/crypt.html
 http://www.upscale.utoronto.ca/GeneralInterest/Harriso
n/QuantTeleport/QuantTeleport.html
 I found very useful an article from the Oct. 4, 2004 St.
Louis Post-Dispatch; a somewhat earlier version can
be found at
http://www.nashuatelegraph.com/apps/pbcs.dll/article?
AID=/20040926/BUSINESS01/209260303