Hi, and welcome to my website! I am Thijs Laarhoven, a postdoctoral researcher at IBM Research in Zürich (Rüschlikon), Switzerland. Previously I was a PhD student at the Eindhoven University of Technology, studying the unrelated topics of collusion-resistant fingerprinting and group testing algorithms, lattice algorithms for solving hard lattice problems, and nearest-neighbor search techniques like locality-sensitive hashing (LSH) and our new method, locality-sensitive filtering (LSF).
Before that, I obtained the degrees of Bachelor of Science (2009) and Master of Science (2011) from the Eindhoven University of Technology, graduating with honors in Industrial and Applied Mathematics. On this website you can find information related to my research, such as a list of publications (with links to freely available copies of these papers), slides of all previous talks I have given, and information with respect to courses which I (co-)taught at the TU/e. The menu above will help you to find what you are looking for.
Below is a short résumé on my previous work experience and education.
Lattice-based cryptosystems are post-quantum cryptosystems based on hard problems on lattices, such as finding the shortest non-zero vector on a given lattice. To assess the actual hardness of breaking these cryptographic primitives, it is essential to obtain a better understanding of the state-of-the-art algorithms that solve these hard problems, and to be able to estimate their computational complexities. In my research I aimed to get a better understanding of, and find improvements for, various of these lattice algorithms, with the main focus on lattice sieving methods for the shortest vector problem.
To protect copyrighted content against piracy, fingerprints or watermarks are commonly embedded in the content, allowing the distributor of the content to trace a pirate copy to the responsible user. To combat this solution, several pirates may collude, and mix their watermarked copies into a new copy, with a fingerprint which is a mix of the individual pirates' fingerprints. With fingerprinting codes it is possible to find the pirates even if they collude. Various previous solutions were aimed at non-adaptive settings, and during my internship I studied adaptive solutions, leading to the invention of the (patented) dynamic Tardos scheme.
The research in my PhD focused on two topics: improving collusion-resistant fingerprinting schemes, and a new direction in lattice sieving algorithms by combining them with nearest neighbor search techniques. Besides the results in these two main topics, it was also shown how to improve upon the state-of-the-art for group testing and nearest neighbor searching. The resulting PhD thesis titled Search problems in cryptography: From fingerprinting to lattice sieving from December 2015 can be downloaded here.
I graduated in the group Coding Theory and Cryptology, which is part of the section Discrete Mathematics. In the second year of my Masters I did a final project combined with an internship at Irdeto BV. This internship concluded with writing a Masters thesis, titled Collusion-resistant traitor tracing schemes, which can be downloaded here.
During these three years of my studies I also took many courses in Computer Science. In the first year I obtained propaedeutic diplomas in both Mathematics and Computer Science, and later I also completed a so-called "minor" in Advanced Computer Science. The last part of these three years focused on discrete mathematics, which concluded with a final project and thesis about the Collatz conjecture. This thesis titled The 3n+1 conjecture can be downloaded here.