## Thijs Laarhoven

#### Cryptographer at TNO

## Welcome

Welcome to my homepage! My name is Thijs Laarhoven, and I am currently a research scientist at TNO, the Dutch Organization for Applied Scientific Research. Before this, I was a postdoctoral researcher at the Eindhoven University of Technology, during which I also held a temporary visiting scientist position at the University of California, Berkeley, for the Spring 2020 semester. Before that, I was a postdoctoral researcher at IBM Research in Zurich, Switzerland. And before that, I completed my PhD at the Eindhoven University of Technology, in the Netherlands.

### Research

### Statistics

#### Citations

2264#### Publications

48#### Talks

60#### Chess title

FM## Resume

### Summary

Besides being able to work independently and setting my own agenda, one of my strengths is to find the right perspective for a complex task, and to see how techniques from other areas can be used to solve these problems efficiently. For instance, in my paper at Crypto 2015 I made a new connection between lattice algorithms and nearest neighbor searching, marking the beginning of a long line of new work on this topic.

### Experience

##### Dec 2021 - present

#### Research Scientist

At TNO, the Dutch Organization for Applied Scientific Research, I contribute to bringing digital security innovations from the lab into the field. This involves going beyond academic research, seeing how technologies can land in society and make a positive impact in government or industry settings, and demonstrating their added value through proof-of-concept demonstrations of the technology. Focus areas at TNO include the migration to quantum-safe cryptography, and finding ways to collaborate on privacy-sensitive distributed data with tools such as multiparty computation and (fully) homomorphic encryption.

##### Nov 2017 - Nov 2021

#### Postdoctoral Researcher

For my postdoc at the TU/e I studied topics related to lattices and nearest neighbor searching, in the context of lattice-based (post-quantum) cryptography, and for various applications that require finding similar items in large databases. For the period 2019-2021, this research was funded by a three-year personal NWO Veni innovational research grant of EUR 250.000, which supports outstanding researchers to pursue their line of research for three years at any Dutch university.

##### Jan 2020 - May 2020

#### Visiting Scientist

During Spring 2020 I was an invited visiting scientist to the research program titled "Lattices: Algorithms, Complexity, and Cryptography" at the Simons Institute for the Theory of Computing. During this program, researchers visited from all around the world to collaborate on open questions in lattice algorithms and lattice-based cryptography, and to discuss ideas and potential new approaches, until in March 2020 the world went into lockdown, and the program came to an early end.

##### Mar 2016 - Sep 2017

#### Postdoctoral Researcher

During my time at the IBM Research lab in Zurich, Switzerland, I studied methods to further improve lattice-based cryptographic solutions, as well as methods that attempt to break these schemes, to get a better understanding of the true security of these lattice-based schemes. I further continued my research on efficient nearest neighbor techniques, which resulted in a nice joint paper on practical and optimal time-space trade-offs.

##### Oct 2011 - Feb 2016

#### Doctoral Candidate

In my PhD research, I focused on obtaining a better understanding of, and finding improvements for, various lattice algorithms that lie at the foundation of
lattice-based cryptanalysis. Specifically, I focused on lattice sieving methods for the shortest vector problem, and I helped transform sieving from a mostly
irrelevant theoretical novelty (2011) to the main algorithm to consider when choosing parameters (2016). The time complexity 2^{0.292n + o(n)} from our
SODA 2016 paper currently still stands as the asymptotically fastest method for solving the shortest vector problem in high dimensions, while the
2^{0.265n + o(n)} from my PhD thesis was long the best quantum complexity for the shortest vector problem, until it was finally improved by Chailloux-Loyer
at AsiaCrypt 2021.

##### Oct 2010 - Jun 2011

#### Research Intern

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.

### Volunteering

##### Oct 2020 - Dec 2021

#### Lichess.org Team Member

Lichess is the second largest online chess site, and each day millions of games are played between users from all around the world. Lichess is free, open-source, ad-free, and exists as a non-profit organization funded solely through donations from users. As a team member I assisted with moderating the chat, finding cheaters, handling ban appeals, developing improved cheat detection tools, scouting and guiding new team members, and outlining the path towards the future for Lichess in terms of policies, governance, goals, vision, and more.

### Education

##### Oct 2011 - Feb 2016

#### PhD in Cryptography (cum laude)

The research in my PhD at the Eindhoven University of Technology (TU/e) 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, I showed 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.

##### Sep 2009 - Aug 2011

#### MSc in Applied Mathematics (cum laude)

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.

##### Sep 2006 - Aug 2009

#### BSc in Applied Mathematics (cum laude)

During the first three years of my studies I took various courses in both Applied Mathematics and 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.

### Skills

- Python
- C
- C++
- Object Pascal
- Java
- Haskell
- HTML
- PHP
- SQL
- CSS
- JavaScript
- Mathematica
- R
- Matlab
- Sage
- Microsoft Office
- LaTeX
- Git
- Dutch
- English
- French
- German