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Quantum Computing and Communications: An Engineering Approach by Ferenc Balazs, Sandor Imre

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10

Quantum-based Key Distribution

Quantum key distribution is one of the most discussed topics of quantum computing. The motivation behind this can be traced back to implementation issues. Namely while construction of a quantum computer is fairly difficult at this moment because we are not able to isolate sufficiently the system from the environment, optical fibers or even the open air proved to be appropriate channels for distribution of cryptographic keys if photons are exploited as quantum bits.

As we have discussed in Chapter 9.1 when we were introducing cryptography in connection with code breaking, secure communications between parties can be provided in two essentially different ways. Both are common in using so-called keys to encrypt plain text messages. Symmetric key cryptography (see Section 9.2) applies the same keys at both communication edges. This approach is theoretically secure. From a practical point of view all the technical problems can be solved efficiently (see Sections 9.2.1 and 9.2.2) only sharing the common key represents a real challenge. Either we design a strongly centralized1 network architecture, e.g. cellular mobile systems, or the parties have to meet regularly to exchange the keys. Public key cryptography (see Section 9.3) is advantageous in a distributed environment because it applies different keys making key exchange obsolete. Unfortunately we have to face the issue that its secureness has never been proven; only a belief shores up our hope that ...

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