Classical Cryptosystems In A Quantum Setting

I hereby declare that I am the sole author of this thesis. I authorize the University of Waterloo to lend this thesis to other institutions or individuals for the purpose of scholarly research. I further authorize the University of Waterloo to reproduce this thesis by photocopying or by other means, in total or in part, at the request of other institutions or individuals for the purpose of scholarly research. ii The University of Waterloo requires the signatures of all persons using or photocopying this thesis. Please sign below, and give address and date. iii Acknowledgements This thesis would not have been possible without much support and assistance. I would like to thank my supervisor, Michele Mosca, for sharing wisdom, experience, and guidance. Thank you to NSERC and the Department of Combinatorics and Optimisation at the University of Waterloo for their generous financial support. Thank you also to Phillip Kaye, Edlyn Teske, and Christof Zalka for many helpful conversations and suggestions.