Cryptography Reference
In-Depth Information
chapter 1
Quantum Cryptography
A. Ekert
University of Cambridge
Contents
1.1 Classical Origins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Le Chiffre Indechiffrable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Not So Unbreakable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Truly Unbreakable? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.5 Key Distribution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.6 Local Realism and Eavesdropping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.7 Quantum Key Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.7.1 Entanglement-Based Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.7.2 Prepare and Measure Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.8 Security Proofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.9 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Few persons can be made to believe that it is not quite an easy thing to
invent a method of secret writing which shall baffle investigation. Yet it
may be roundly asserted that human ingenuity cannot concoct a cipher
which human ingenuity cannot resolve
...
— Edgar Alan Poe, “A Few Words on Secret Writing,” 1841
Abstract
Quantum cryptography offers new methods of secure communication. Un-
like traditional classical cryptography, which employs various mathematical
techniques to restrict eavesdroppers from learning the contents of encrypted
messages, quantum cryptography is focused on the physics of information.
The process of sending and storing information is always carried out by phys-
ical means, for example photons in optical fibers or electrons in electric cur-
rent. Eavesdropping can be viewed as measurements on a physical object — in
