On 11 March Robbert de Haan (CWI) received his PhD in mathematics at Leiden University with his thesis Algebraic Techniques for Low Communication Secure Protocols.
Internet communication is often encrypted with the aid of mathematical problems that are hard to solve. Another method to secure electronic communication is the use of a digital lock of which the digital key must be exchanged first. PhD student Robbert de Haan (CWI) researched models for a guaranteed safe communication between two people without the exchange of a digital key and without assumptions concerning the practical difficulty of solving certain mathematical problems.
In ancient times Julius Caesar used secret codes to make his messages illegible for spies. He upped every letter of the alphabet with three positions: A became D, Z became C, and so on. Usually, cryptographers research secure communication between two people through one channel that can be monitored by malevolent people. De Haan studied the use of multiple channels. A minority of these channels may be in the hands of adversaries that can intercept, replace or block the message. He proved the most efficient way to securely communicate along these channels and thus solved a fundamental cryptography problem that was introduced almost 20 years ago by Dole, Dwork, Naor and Yung.
Robbert de Haan is also active in multi-party computation - secure computations with input from multiple parties with mutual distrust. An example is electronic voting, where everybody wants to know the correct results but where individual votes have to remain anonymous. Current multi-party computation techniques need a large amount of data to perform calculations; there is an enormous communication overhead. This makes them less appropriate for calculations on large quantities of data, like corporate statistics that should be securely compared. De Haan developed advanced mathematical techniques to reduce the overhead for many of these calculations. His results can also be applied to make other cryptography protocols more efficient. They already played an unexpected but crucial role in a breakthrough in communication-efficient zero knowledge evidence techniques. This research was partly financed by the Bsik-BRICKS project PDCI.
More information: www.cwi.nl/en/Cryptology