Kristoffer Opsahl

Kristoffer Opsahl

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My Alacritty, Zellij, and Helix Development Setup

My Alacritty, Zellij, and Helix Development Setup

This article is a public note-to-self where I'll go through the basic configuration I use to get new computers ready for programming in just a couple of minutes. It is centered around the following pieces of software: * Alacritty, a terminal. * Zellij, a terminal multiplexer. * Helix, a text-editor with

Breaking AES-ECB with an Encryption Oracle Attack

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Breaking AES-ECB with an Encryption Oracle Attack

This is a write-up of one of the challenges from this year's TG:Hack. I wrote about my participation in another post: 3rd Prize at TG:Hack. Background TG:Hack is a Capture-the-Flag competition where the objective is to identify and leverage security flaws in various entities. As

3rd Prize at TG:HACK

3rd Prize at TG:HACK

I recently participated in TG:Hack, which is Norway's largest Capture The Flag (CTF) competition. It is hosted at and is a part of Norway's largest LAN party: The Gathering. The competition runs over four days, and the goal is to leverage your knowledge of computers,

Java's Optional has a Problem

Java's Optional has a Problem

Java's Optional is over a decade old, and has been subject to intense debate since long before its release. With this in mind, I will argue a particular aspect of its design was a rather unfortunate mistake, and show how it can lead to bugs. I will moreover

From Zero to Hello World with Apache Kafka® in 2025

From Zero to Hello World with Apache Kafka® in 2025

This is a guide on how to run Apache Kafka® locally, and how to start using it. I found the resources I used myself to be needlessly and frustratingly complicated, as well as outdated. Thus my goal is to give a simple set of instructions that works almost everywhere, regardless

Core Concepts in Apache Kafka®

Core Concepts in Apache Kafka®

This post is intented to give a high-level description of the basic components of Apache Kafka® (Kafka) for someone that is entirely new to it, and that is sufficient to get building. For significantly more detail and nuance, refer to the official documentation. Records Records are the fundamental units of