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The Blockchain An Introduction to Blockchain, Bitcoin ₿, and related concepts An example of a blockchain. Image by Martin Thoma. Bitcoin crossed $40,000 USD for the first time recently, so it’s again in the news. Bitcoin is just the most-known cryptocurrency. It is one application using a blockchain. In this article, I will walk you through some core concepts … Read More »

6 YAML Features most programmers don’t know Level-up your YAML knowledge to write cleaner YAML files YAML is a file format commonly used for data serialization. There are a plethora of projects using YAML files for configuration, such as Docker-compose, pre-commit, TravisCI, AWS Cloudformation, ESLint, Kubernetes, Ansible, and many more. Knowing the features of YAML helps you with all of them. Let’s cover the basics … Read More »

365 Main Dishes This is an article I had for quite a while as a draft. As part of my yearly cleanup, I've published it without finishing it. It might not be finished or have other problems. I don't want to spend a lot of thought into what I'm going to eat. I'm … Read More »

Online-Schule The following article proposes to build an online school. It is a thought I have for many years. It has become way more important recently. It is written in German 🇩🇪, but you can use deepl.com to translate it. Die Corona-Pandemie hat die Welt hart getroffen. Bei vielen meiner Kunden … Read More »

Full Disk Encryption 😇 Keep your data private, even if you lose your device Having an attacker with physical access to your device is one of the worst scenarios. If the data is not encrypted on the disk, then the attacker can simply disassemble your device, get the HDD/SDD, put it in his machine, and read the data. For this reason, encrypting your … Read More »

DOS via a billion laughs 😈 Consume arbitrary much RAM by repeated referencing Image by the author The billion laughs attack is known since 2003 (source). The attack uses the references in XML files to make a small source file be huge in memory if all references are expanded. It’s also known as a LOL bomb, XML bomb, or in a variation … Read More »

Effective Access Control 😇 Access control is the act of restricting access to a selected group of people or systems. That group is authorized to access the system. To check if a person is authorized to access, the person typically has to be authenticated. In this article, I focus on web services. Access to … Read More »

Software Composition Analysis (SCA) The job as a software developer is pretty crazy: You need to learn constantly about new technologies, understand topics within the domain you’re working, estimate how long it will take to build stuff you have never built before, explain issues to people who have absolutely no clue. On top … Read More »

Email Spoofing 😈 Learn what it is, how it works, and how to defend against it with SPF, DKIM, DMARC Email spoofing is the creation of emails with a forged sender address. Faking the senders’ address is often a part of a phishing attack. There are different ways to fool the victim of a phishing attack about who is the real sender: Using slightly different sender domains like [email protected] … Read More »

Pythons Scoping Rules The extraordinary short guide to Pythons crazy scoping rules It’s obvious that you cannot access a variable before it was declared. But if it was declared inside a loop, can you access it outside a loop? If it was declared in a function, can you access the variable outside of the function? This kind of “variable lifetime” is … Read More »