34,306 research outputs found
A Talk on Quantum Cryptography, or How Alice Outwits Eve
Alice and Bob wish to communicate without the archvillainess Eve
eavesdropping on their conversation. Alice, decides to take two college
courses, one in cryptography, the other in quantum mechanics. During the
courses, she discovers she can use what she has just learned to devise a
cryptographic communication system that automatically detects whether or not
Eve is up to her villainous eavesdropping. Some of the topics discussed are
Heisenberg's Uncertainty Principle, the Vernam cipher, the BB84 and B92
cryptographic protocols. The talk ends with a discussion of some of Eve's
possible eavesdropping strategies, opaque eavesdropping, translucent
eavesdropping, and translucent eavesdropping with entanglement.Comment: 31 pages, 8 figures. Revised version of a paper published in "Coding
Theory, and Cryptography: From Geheimscheimschreiber and Enigma to Quantum
Theory," (edited by David Joyner), Springer-Verlag, 1999 (pp. 144-174). To be
published with the permission of Springer-Verlag in an AMS PSAPM Short Course
volume entitled "Quantum Computation.
Coherent State Quantum Key Distribution with Entanglement Witnessing
An entanglement witness approach to quantum coherent state key distribution
and a system for its practical implementation are described. In this approach,
eavesdropping can be detected by a change in sign of either of two witness
functions, an entanglement witness S or an eavesdropping witness W. The effects
of loss and eavesdropping on system operation are evaluated as a function of
distance. Although the eavesdropping witness W does not directly witness
entanglement for the system, its behavior remains related to that of the true
entanglement witness S. Furthermore, W is easier to implement experimentally
than S. W crosses the axis at a finite distance, in a manner reminiscent of
entanglement sudden death. The distance at which this occurs changes measurably
when an eavesdropper is present. The distance dependance of the two witnesses
due to amplitude reduction and due to increased variance resulting from both
ordinary propagation losses and possible eavesdropping activity is provided.
Finally, the information content and secure key rate of a continuous variable
protocol using this witness approach are given
Optimal eavesdropping in cryptography with three-dimensional quantum states
We study optimal eavesdropping in quantum cryptography with three-dimensional
systems, and show that this scheme is more secure than protocols using
two-dimensional states. We generalize the according eavesdropping
transformation to arbitrary dimensions, and discuss the connection with optimal
quantum cloning.Comment: 4 pages, 2 figure
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