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Title: Innovative eavesdropper attacks on quantum cryptographic systems
Author: Newton, Elizabeth
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2018
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Quantum cryptography aims to provide secure communications, no matter how powerful or resourceful an eavesdropper is. As long as the eavesdropper is constrained by the laws of physics, she can never break the underlying cryptographic system. One of the key applications in quantum cryptography is key distribution. This involves the creation and sharing of the cryptographic key, the element of the message which provides secrecy between the sender and the recipient. There are two main forms of quantum key distribution. The first uses discrete variables, where information is encoded onto discrete modes of light, such as the polarisation of single photons. The second uses continuous variables, where information is encoded onto an infinite dimensional space, such as the quadratures of coherent states of light, which generally consist of several photons. Here, an additional approach is examined. It falls under the category of continuous variable quantum key distribution, but instead of coherent states, such as those produced by lasers, it uses thermal states, produced by thermal sources of light. First, the experimental properties of thermal states are examined and compared to those of coherent states, then a simple key distribution model is constructed to test if thermal states are viable as a resource for secrecy. The initial results look promising. When using continuous variables for key distribution, information is encoded by using randomly generated quadratures with a Gaussian distribution. Several methods for discretising these quadratures into key bits are examined to see if they have security implications associated with them. It is found that a poor choice of discretisation method can leak information to an eavesdropper. Once the quantum transmission is complete for key distribution, some classical error correction needs to be performed. A new eavesdropping technique for an eavesdropper to attack one of these forms of error correction, cascade, is described. We find that more attention needs to be paid to the classical parts of quantum key distribution in order for it to succeed.
Supervisor: Varcoe, Benjamin T. H. ; Razavi, Mohsen Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available