Hi There! 👋

My name is Arjen and I am the Manager of Product Development and Chief Lecturer at Hogeschool NOVI. I work on creating the most modern and relevant educational products that we can offer. Through stategic partnerships and attracting the most talented content developers we offer world class education to our students.

In my work as Chief Lecturer for Cybersecurity I focus on teaching students all there is to know about the technical side of Cyber Security. My main areas of expertise are Reverse Engineering, Infrastructure Security and Web Application Security.

Next to my work I am active as an Independent Hacker. I assist my customers in their journey to increase their security posture. I do this through advice, seminars and security assessments. I toot on the fediverse as @credmp@fosstodon.org.

I organize the Dutch meetup for Hack The Box, for which I am the ambassador in The Netherlands. Each month, on the 3rd Wednesday, members of the Dutch cyber security community get together and have presentations, demos and discussion on wide ranging topics. Through this collaboration I have become an Ambassador for Hack The Box.

Find my longer form writings in the Writing Category.

The views on this site are my own.

The cyber cafe podcast

Last week I was a guest on the Cyber Cafe podcast by rootsec. It was a fun discussion on education and the current xz backdoor story. It is in the Dutch language. It is available on youtube and included below:

April 9, 2024 - 1 min Arjen Wiersma

Microsoft Teams (v2) on Linux

This post is just a small note for those of you who also run Microsoft Teams on Linux through their browser and now receive a note “your browser does not meet the requirements for the new Teams”. It turns out that the client is looking at the user-agent string to determine which browsers it accepts, and which not. So, if you have the message, install an user-agent switcher and select a common browser on a common OS (from the MS perspective) and you will suddenly meet the requirements....

April 1, 2024 - 1 min Arjen Wiersma

My computing environment

This is a longer form article. I is relevant as of February 18th 2023. If the circumstances of my environment changes I will try to update this article to reflect the situation. You can find the full source code of my dotfiles on Github. I like consistency and simplicity. I do not like to use many different tools to do different things, I rather spend my time learning to use a few tools very well then to follow the hype on the latest trend of tools for something we have been doing forever....

February 18, 2024 - 7 min Arjen Wiersma

Heading to the finish line

It has been a little while. I have been swamped with work and the work on my thesis, leaving no room to finish the Advent of Code or much of anything else. Yesterday I gave my practice presentation for my thesis. This means I am one more step closer to the finish line. During the day there were many interactions with fellow students. One of the topics has been the templates to use at Open Universiteit....

February 17, 2024 - 1 min Arjen Wiersma

Advent of Code 2023 day 9

The weekend generally is a place to find hard puzzles again, this time not so much. A simple quest to find the next number in a sequence with a fully written out algorithm to follow. They key here is to use recursion. package main import ( "fmt" "time" "arjenwiersma.nl/aoc/internal/aoc" ) func NextStep(in []int) int { allZero := true for _, v := range in { if v != 0 { allZero = false } } if allZero { return 0 } var diffs []int for i := 1; i < len(in); i++ { diffs = append(diffs, in[i]-in[i-1]) } p := NextStep(diffs) return in[len(in)-1] + p } func main() { content := aoc....

December 9, 2023 - 1 min Arjen Wiersma

Advent of Code 2023 day 8

Somewhat suspicious of 2 easy days we end up at Day 8. A simple map to follow again, from one key follow the instructions until we hit ZZZ. Part 2 had us do it for several keys at once, with the goal to find the spot where they all converge. This can take forever, erhm, a long time. So there has to be a math type solution to this problem. It turns out to be a Least Common Multiple problem....

December 9, 2023 - 2 min Arjen Wiersma

Advent of Code 2023 day 7

Today we learned about CamelCards, a game of poker meant to play on the back of a camel. The most interesting part here was the parsing of the cards and figuring out how to properly rank them. Part 2 turned out to be as easy as tracking Jokers. package main import ( "fmt" "sort" "strconv" "strings" "time" "arjenwiersma.nl/aoc/internal/aoc" ) type Card struct { bid int hand []int jokers int } func (c *Card) strongerThen(o *Card) bool { for i, v := range c....

December 9, 2023 - 3 min Arjen Wiersma

Advent of Code 2023 day 6

Day 6 turned out to be the easiest day in the range so far. A simple implementation of the algorithm was more than sufficient. I later learned that it was a quadratic function. On the subreddit Deatranger999 said: If you hold down the button for x seconds, then you will beat the distance if the quadratic x^2 - t x + d is at most 0, where t is the total time of the race and d is the distance you’d like to beat....

December 9, 2023 - 2 min Arjen Wiersma

Advent of Code 2023 day 5

Today was an interesting problem. We are basically given a map to follow based on a number, possibly transforming the number at each step. With a single number this is quite simple, just apply the rules and step through each set of transformations. The problem becomes tricky when it turns out we have to deal with enormous ranges of numbers. On the subreddit some people reported their implementation to take hours and use 20GB of memory....

December 9, 2023 - 3 min Arjen Wiersma

Advent of Code 2023 Day 4

The difficulty is going up and down. This day was quite easy in comparison to yesterday. Today it was about parsing some numbers and finding a set of winning numbers. As I am doing these puzzles in Go I found out that there is no default set type. There is an implementation by HashiCorp named go-set that fills this void. I did not use an external package (I try to avoid them while doing AoC), but I am very tempted to pull that package in....

December 4, 2023 - 2 min Arjen Wiersma