Cryptography is the art of secrecy. Nearly as old as the art of writing itself, it concerns itself with one of the most fundamental problems faced by any society whose success crucially depends on knowledge and information.
Traditional cryptography is concerned with the secure and reliable transmission of messages. With the advent of widespread electronic communication and the internet, however, new cryptographic tasks have become increasingly important. We would like to construct secure protocols for electronic voting, online auctions, contract signing and many other applications where the protocol participants themselves do not trust each other. Unfortunately, it is impossible to implement such protocols with unconditional security, even using quantum mechanics. Classically, such primitives can be implemented under the unproven assumption that factoring large numbers is difficult. Hence, at least once a quantum computer is built that makes it easy to factor numbers, such protocols will be broken.
Stephanie Wehner's thesis "Cryptography in a quantum world" proposes a new model for implementing such protocols where we make the realistic assumption that storing quantum states is difficult. That is, we will experience small amounts of noise when we try to store a quantum state. It is proven that such protocols can indeed be implemented securely under this assumption.
On 27 February 2008 Wehner received her PhD at the University of Amsterdam. Her research was carried out at CWI and supervised by Harry Buhrman, head of the Quantum Computing and Advanced Systems Research Group. Stephanie Wehner accepted a position at the prestigious California Institute of Technology (CALTECH).
More information about this research project can be found on the homepage of Stephanie Wehner: http://homepages.cwi.nl/~wehner/.