Academic C.V.

PhD research

2014-current: PhD student (part-time) at the Radboud university

Promotor: Bart Jacobs

Supervisor: Erik Poll

Papers

  • Koens, T., & Poll, E. (2020), Blockchain Utility in Use Cases: Observations, Red Flags, and Requirements, to appear
  • Koens, T., & Poll, E. (2020), Drivers and Impediments: Experts Opinions on Blockchain Adoption in the Netherlands, to appear
  • Koens, T., Van Aubel, P., & Poll, E. (2020). Blockchain adoption drivers: The rationality of irrational choices. Concurrency and Computation: Practice and Experience, e5843.
  • Koens, T., & Poll, E. (2019). Assessing interoperability solutions for distributed ledgers. Pervasive and Mobile Computing, 59, 101079.
  • Gündlach, R., Hoepman, J. H., van der Hofstad, R., Koens, T., & Meijer, S. (2019). Hydra: A Multiple Blockchain Protocol for Improving Transaction Throughput. arXiv preprint arXiv:1910.06682.
  • Morais, E., Koens, T., Van Wijk, C., & Koren, A. (2019). A survey on zero knowledge range proofs and applications. SN Applied Sciences, 1(8), 946.
  • Koens, T., & Poll, E. (2018, August). The drivers behind blockchain adoption: The rationality of irrational choices. In European Conference on Parallel Processing (pp. 535-546). Springer, Cham.
  • Koens, T., & Poll, E. (2018). What blockchain alternative do you need?. In Data Privacy Management, Cryptocurrencies and Blockchain Technology (pp. 113-129). Springer, Cham.

Articles

Students co-supervised (needs to be updated)

  • Job Douma (2020), Security Analysis of Trustchain. Research internship, (@Radboud University, together with Erik Poll)
  • (@Radboud University, together with Erik Poll)
  • Casper van Ginneken (2019), Settlement of Cross-Border Transactions through Central Bank Digital Currency. Master thesis, (@ING, together with Bert Bruggink)
  • … (@Radboud University, together with Egbert-Jan Sol)
  • … (@Radboud University, together with Marko van Eekelen)
  • Stijn Meijer (2018), …. Master thesis, (@Radboud University, together with Erik Verheul)
  • Stijn Meijer (2017), … Research internship, (@Radboud University, together with Bart Jacobs)

Teaching

<lectures provided>

Journals

<reviewed papers>

Extended drivers paper accepted

An extended version of our drivers paper has been accepted at Concurrency and Computation: Practice and Experience, Wiley, 2020.

In this extended version we evaluate three more use cases. These analysis suggests that, similar to our previous paper, blockchain may not be the best technological choice. As such, choosing blockchain as a technology in these use cases seems like an irrational choice.

Our drivers may explain the rationality behind this seemingly irrational choice.

Surveying Organizational Threats of Blockchain

In a recent study that I did on blockchain use cases, I found that most use cases focus on addressing a particular use case problem with blockchain. However, what consistently was lacking was a discussion of potential threats that are introduced when applying blockchain. From an empirical perspective, I also find that in practice blockchain advocates tend to focus on addressing the use case problem with blockchain, and the threats of blockchain are usually not mentioned.

Personally, I’m a huge fan of blockchain and distributed ledger technology. However, I believe these technologies should be applied where necessary; these technologies should not be applied where possible. Applying these technologies where it could be applied may introduce unnecessary threats.

Although several good surveys exist on the security and privacy threats of blockchain, see for example the work by Li et al. and Conti et al. , there is no survey of organizational risks.

In this white paper we survey potential organizational threats for use cases that adopt blockchain. We grouped the 22 threats in two categories, 1. Threats caused by human behavior, and 2. Threats caused by blockchain. Our survey complements the existing work on security and privacy threats of blockchain. These surveys can be used for the identification of blockchain risks in use case that (plan to) adopt blockchain.

Any feedback is again welcome either through Linkedin or email.

A Game of Material and Activity

Here’s a game I played with the black pieces (online) which show the importance of activity of one’s pieces, or, the consequences when there is a major lack of piece activity. In short, I sacrificed material to severely limit the activity of my opponent’s knight, bishop and rook. In the end, it all payed off, as almost all of his pieces were immobilized.

1.b4 d5

2.e3 Bf5

3.Bb2 Nd7

4.a3 Ngf6

5.Nf3 e6

6.Bb5 c6

7.Ba4 Be7

After Bb3 the idea of trapping the bishop came to mind. But first finishing development.

8.O-O O-O

9.h3 b5

10.Bb3 a5

11.bxa5 c5

Here we go. Sacrificing a pawn to immobilize the white squared bishop.

12.c3 c4

13.Bc2 Bxc2

But now white’s entire Queen side becomes passive. Look at the knight on b1, it literally can’t go anywhere. The dark-squared bishop on c1 and the rook on a1 are not active either. Ideally, I want a black knight on a4, a black pawn on e4, and a black knight on d3, and those white pieces will be burried alive.

14.Qxc2 e5

Nc5 immediately may have been better as a4 is white’s freeing move.

15.Qf5 e4

16.Nd4 Nc5

17.Ra2 Na4

18.Ba1 Rxa5

19.Nc6 Qc7

20.Nxa5 Qxa5

And that’s black rook for a white knight. However, that knight (and white’s Queen) are its only active pieces.

21.g4 Qd8

22.h4 Qd7

23.Qxd7 Nxd7

24.g5 Ne5

25.Kg2 Nd3

See my comment at move 13. Mission accomplished. I’m down in material (2 points), but white simply can’t use his Queen-side forces (11 points).

26.Kh3 f6

27.gxf6 Rxf6

28.f4 exf3

29.h5 f2

30.Kg4 g6

White resigned. None of his pieces (except for the king) can move.

Blindfolded timed chess game

Today (21-10-2019) I was challenged to a game of chess with the black pieces. Nothing special, as it happens 50% of the time. However, in this case I was blindfolded (literally) and the game was timed (9 minutes per person for the whole game).

My opponent told me his moves, and I told him mine. He moved both the white and black pieces, and handled the clock for both sides (pretty fair ;-)).

Here is how the game went:

  1. e4 c6
  2. Nf3 d5
  3. Nc3 Bg4
  4. Be2 e6
  5. 0-0 Nf6
  6. d4 dxe4
  7. Ne5 Bxe2
  8. Qxe2 Qxd4
  9. Bf4 Be7
  10. Rad1 Qb4 – The Silicon Monster even likes white position. White has a lead in development, and the black king will be stuck in the center.
  11. Rb1 too passive. 0-0
  12. f3 -trying to complicate matters, but now the position is lost. exf3
  13. Rxf3 Nbd7
  14. Nxd7 Nxd7
  15. Rh3 Bc5+ (I missed Qxf4, winning the bishop.)
  16. Be3 Rad8
  17. Qh5 Bxe3+
  18. Kh1 Bh6
  19. Re1 Nf6
  20. Qe2 Bd2
  21. Rf1 Bxc3
  22. bxc3 Qe7
  23. Rxf6 Qxf6 – 1 minute on the clock!
  24. Qh5 Qg6 – Missed a mated in one 🙂 Qf1++ Time pressure and being blindfolded don’t mix well.
  25. Qd1 A final trick Rxd1++ Black sees it, it’s just mate.

Not too bad. Next time, two boards blindfolded!

Single digit shoot

Yes! Two more goals achieved. Single digit body fat (8%) and finished a photo-shoot.

After months of following a strict diet, cardio at 05:30 in the morning, and fitness training 5 times a week I was ready for the gruesome last week of photo-shoot prepping. Dropping caloric intake to max 1700 kcal (which used to be 5500 kcal max at some point last year) and very low in carbohydrates, this became a mental challenge due to the complete lack of energy.

The cheat meal the evening before the shoot was divine.

Thanks to Kenneth Nwosu who is an awesome photographer. He is able to make you feel more relaxed during the shoot, provides great advice, and the results are incredible. Follow Kenneth or have a look at his collection on instagram, twitter, or his website.

Thanks to everyone else who supported me during these last few weeks. Photos are available upon request.

Prepping for the shoot was a great experience, one I wouldn’t recommend to anyone 🙂

Beating a computer at chess (max level)

Now and then I play a quick game of chess against on my mobile phone. We all know that computers are much better at the game nowadays. I’m impressed by the way modern chess computers play, and here’s another example. However, now and then I manage to beat the computer (AI Factory), which has an estimated elo rating of around 2000. Here’s a nice example of me winning a chess game against a computer at max level, within 20 moves:

“][Date “2019.04.11”][White “U”][Black “Cpu (12)”][PlyCount “37”][Result “1-0”]
1. e4 c5 2. Nf3 e6 3. d4 a6 4. d5 exd5 5. exd5 d6 6. c4 Bf5 7. Nc3 Nd7 8. Bd3 Ne7 9. O-O g6 10. Re1 Bxd3 11. Qxd3 Bg7 12. Bf4 Nb6 13. Ne4 Nb6c8 14. Bg5 O-O 15. Bf6 b5 16. Bxg7 Kxg7 17. Qc3+ Kh6 18. Nf3g5

Final position after Nf3-g5, in which black resigned. The black king is in trouble.