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The Impossibility of Keyless Communication in Quantum Cryptography

✍ Scribed by Daniel Greenberger; Mark Hillary

Publisher
John Wiley and Sons
Year
2000
Tongue
English
Weight
100 KB
Volume
48
Category
Article
ISSN
0015-8208

No coin nor oath required. For personal study only.

✦ Synopsis

We define a keyless communication as a message sent from one party (Alice) to another (Bob), such that the message is totally secure. This means that if a third party (Eve) is trying to eavesdrop, she will receive only random bits. She cannot understand the content of the message, even if she is able to intercept it in such away that Alice and Bob do not know it has been intercepted. For such a totally secure message, Alice and Bob do not need to set up any key beforehand, as it can add no further security.

Starting with a system that we felt sure met such criteria, we were shocked to find out that it could be broken in at least two ways, by a semi-classical method and by a quantum method, such that Eve could read a message and Alice and Bob would not know it. Alice and Bob can counter such eavesdropping, but only by sending out test messages. This will enable them to ascertain that Eve is on the line, but then she can still occasionally pick up snippets of their conversation. In that case, in order to be totally secure, it is better to establish an unbreakable key beforehand.

We postulate and give plausibility arguments that in general it is impossible to establish keyless communication between two parties.

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