The University of Bristol has been developing a free-space, low cost, test-bed quantum cryptography system for the past five years, and the work in this thesis is 'concerned with the algorithms and protocols used in this system. The use scenario is that a hand-held, Alice, device can be used in conjunction with a fixed terminal, Bob, to expand an existing store of shared secret key bits between the two parties. This requires that both devices are compact and low-cost, but with the hand-held Alice device being more so, as there will be a high of ratio of these to Bob devices. To both satisfy the cost constraint and allow rapid prototyping, the physical setup uses off-the-shelf optical and electrical components. The first part· of the work in this thesis analyses the security and performance implications of implementation imperfections. In order to produce a secret key string, novel data processing and reconciliation algorithms are described, optimisation for the scenario where the Alice device has less computational power than that of Bob. Specifically, clock-period recovery, elimination of the background noise by temporal gating, and synchronisation, with low-density parity-check (LDPC) codes being used for the error correction ·stage. In light of recent results on the security of quantum cryptography systems, estimates are calculated that show that the hardware needs to be further improved in order to expand the key store in a convenient period of time. Several improved models are simulated that explore the modifications required to bring the key expansion times into an acceptable range.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:654561 |
| Date | January 2010 |
| Creators | Godfrey, Mark |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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