Quantum physics, quantum computation and cryptography.
My research extends over most aspects of information processing in quantum-mechanical systems. It is a cross-disciplinary field bringing together theoretical and experimental quantum physics, computer science and information theory. Its scope ranges from deep fundamental issues in physics to prospective commercial exploitation by the computing and communications industries.
My work is mostly theoretical but its results also bear directly on issues of experimental implementation. One reason why it has attracted attention from industry and government agencies is that quantum cryptography can guarantee perfectly secure communication. Another is that projected quantum computers will be capable of efficiently solving some problems (including factorisation, which has a bearing on cryptanalysis) for which there is believed to be no efficient classical algorithm.
In this video from the Centre for Quantum Technologies at the National University of Singapore, Professor Ekert explains what it takes to keep our secrets secret.