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There is nothing wrong with considering a blockchain whenever you have data to store and handle. The important point to take note of is: blockchain is probably not the right tool for your problem, despite being an exciting technology. But how do you systematically think through the options and decide wither to use a blockchain or one of the many alternatives to blockchain?

Several groups have come up with their take on “When to use blockchain?” independently. This includes academic researchers, the Hyperledger consortium, and the National Institute of Standards and Technology (NIST) of the USA. Their answers are geared…


Let’s start with a disclaimer: This article will not explain blockchain to you, but rather help yo to understand the different aspects and levels of it so you can systematically approach the topic. Afterwards, you will be able to go out and find the right resources for your needs, rather than get lost in the sheer amount of information and the breadth of the topic.

Blockchain, depending on your perspective, promises or threatens to affect a wide range of people, institutions, and businesses. Or maybe you’re not buying into the hype. Should you be informed about blockchain nevertheless? And if…


Blockchain is blowing up. Fueled by a combination of VC capital, government interest and investment, and the internet hype machine, experts are bracing for a coming disruption.

And yet — we do not yet have a clear idea of what that disruption will look like. At this point, the blockchain disruption is (like other legendary objects of apprehension and anxiety) “unknowable, but certain”. “Unknowable” because we do not yet know exactly which implementations or variations of this technology will be the most important or impactful. Yet “certain” because it gives the power to the people rather than middlemen, potentially affecting…


Blockchain is often presented as a novel way to store data. The data storage is often explained as a distributed ledger. I think this emphasis of the ledger-ness is misleading and hides its potential. In a ledger, the emphasis is on accounting and bookkeeping (see e.g. this definition). In the following, I will outline how a blockchain do more, in particular store program state, a crucial component for the distributed execution of programs, smart contracts or chain code, and point to current implementations of this idea. …


We’ve heard a lot about Bitcoin and smart contracts lately. “Blockchain” more generally has been widely hailed as a “game changing” technology: Venture capital has poured 100s of million into start-ups providing services that either directly interface a certain blockchain (e.g. wallet services) and their interplay with the rest of the world (e.g. currency exchanges, payment services), or that pursue novel applications of blockchain-based solutions. As investment has grown, it has become apparent that blockchains can do so much store much more than just financial ledgers, and a number of industries are bracing for disruption.

And yet: only a very…


Distributed consensus finding between untrusted nodes is the key ingredient in blockchain systems. Whether mining “proof-of-work” or minting “proof-of-stake” algorithms are used, the consensus established algorithmically guarantees a consistent view of the data stored in the blockchain, e.g. who owns which bitcoins on the bitcoin blockchain. Consensus algorithms in itself are not a necessarily new, but their unique setting and the way they contribute to blockchain systems were a technical novelty when bitcoin arrived (learn more in my older posts, e.g. here and here). But beyond this “technical” layer of consensus, there are more layers of consensus directly involving humans…


Blockchain systems are run by honest participants, e.g. the miners in case of proof-of-work blockchains like Bitcoin. A rational but malicious participant, only caring about his own profits rather than the health of the network, can choose between participating honestly or attacking the network e.g. via a double-spending attack. How should he choose? Here’s the guide, a high-level summary of the research paper On the security and performance of proof of work blockchains by Arthur Gervais.

What does a participant stand to gain from either honest or dishonest behavior? In the case of honest mining, i.e. verifying blockchain data, the…


Any computer network can be attacked and blockchains running on distributed networks are no different. But the types of attacks blockchains are vulnerable to are somewhat different: in most cases, attackers must focus on manipulating the consensus process in order to hack or alter any information on a blockchain, rather than compromising anything like a password or firewall. In the following, I will explain the structure that hackers manipulate when trying to attack a blockchain secured by a proof-of-work consensus algorithm and will go over the most common types of attack: the 51% attack and double spending. …


Today, on the 7th of February, it has been 25 years since the signing of the Maastricht treaty, also known as the Treaty on European Union. It was signed by 10 states: Belgium, Denmark, France, Germany, Greece, Ireland, Italy, Luxembourg, Netherlands, Portugal, Spain, and United Kingdom.

Besides claims that the EU has its deficits politically, it also lacks identification and identity: Very few people within the EU strongly identify as members of a “european culture”. There is even a MOOC available on it.

Nevertheless, the EU helped in accomplishing peace for an unprecedented time now:


Blockchain technologies top the lists of 2017’s hot trends. Many companies already back their products with blockchain technologies. Competitors use different approaches to blockchain technologies, emphasizing different aspects and pitching them as features to their customers. In this post I will provide an overview of the role of one of those particular aspects of blockchain technologies — “consensus”.

Blockchains are diverse and can be approached from a variety of perspectives. For the sake of this article, I would like to define a blockchain as a public, decentralized database, that keeps public records in an append-only fashion. Moreover, once added into…

Chris Hammerschmidt

Founder at www.apta.tech · Machine Learning for your Software Systems · previously @uni.lu @tudelft

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