Blockchain is a digital concept to store data. This data comes in blocks, so imagine blocks of digital data. These blocks are chained together, and this makes their data immutable. When a block of data is chained to the other blocks, its data can never be changed again. It will be publicly available to anyone who wants to see it ever again, in exactly the way it was once added to the blockchain. That is quite revolutionary, because it allows us to keep track records of pretty much anything we can think of (to name some: property rights, identities, money balances, medical records), without being at risk of someone tampering with those records. If I buy a house right now and add a photo of the property rights to a blockchain, I will always and forever be able to prove that I owned those rights at that point. Nobody can change that piece of information once it is on a blockchain . So — Blockchain is a way to save data and make it immutable. That sounds great, but the big question of course is: how does that work?

Step 1 — Transaction data

Alright, let’s start off with an example: the Bitcoin blockchain. The Bitcoin blockchain is the oldest blockchain in existence. The blocks on the Bitcoin blockchain consist of approximately 1 MB of data each. At the time of writing it counts about 525,000 blocks, meaning roughly a total of 525,000 MB has been stored on this blockchain. The data on the Bitcoin blockchain exclusively exists out of transaction data in regard to Bitcoin transactions. It is a giant track record of all the Bitcoin transactions that have ever occurred, all the way back to the very first Bitcoin transaction. In this article we will assume that a blockchain stores transaction data, just like the Bitcoin blockchain.

Step 2 — Chaining the blocks (with a hash)

Three blocks, all containing some transaction data. Not quite special yet. You can compare it to some stand-alone word documents that simply describe what transactions have occurred and how these have impacted certain balances. Document 1 would then chronologically describe the first transactions that have occurred up to 1 MB, whereafter the next transactions would be described in document 2 up to another MB, and so on. These documents are the blocks of data. These blocks are now being linked (aka chained) together. To do this, every block gets a unique (digital) signature that corresponds to exactly the string of data in that block. If anything inside a block changes, even just a single digit change, the block will get a new signature. How this works? This happens through hashing and will be thoroughly explained later in step 3.

Let’s say block 1 registers two transactions, transaction 1 and transaction 2. Imagine that these transactions make up a total of 1 MB (in reality this would be much more transactions). This block of data now gets a signature for this specific string.

Step 3 — How the signature (hash) is created

So, let’s picture a block again; block 1. Block 1 is a record of only one transaction. Thomas sends 100 Bitcoin to David. This specific string of data now requires a signature. In blockchain, this signature is created by a hash function. A cryptographic hash function is a very complicated formula that takes any string of input and turns it into a unique 64-digit string of output. You could for example insert the word ‘Jinglebells’ into (there are other variants of hashing algorithms as well, but we use this one for this example), and you will see that the output for this specific string of data.

Step 4 — When does the signature qualify, and who signs a block?

A signature doesn’t always qualify. A block will only be accepted on the blockchain if its digital signature starts with — for example — a consecutive number of zeroes. For example; only blocks with a signature starting with at least ten consecutive zeroes qualify to be added to the blockchain. However, as explained in chapter 3, every string of data has only one unique hash bound to it. What if the signature (hash) of a block doesn’t start with ten zeroes? Well, in order to find the block a signature that meets the requirements, the string of data of a block needs to be changed repeatedly until that specific string of data leads to a signature starting with ten zeroes. Because the transaction data and metadata (block number, timestamp, et cetera) need to stay the way they are, a small specific piece of data is added to every block that has no purpose except for being changed repeatedly in order to find an eligible signature. This piece of data is called the nonce of a block. The nonce is a completely random string of numbers (note: pictures show other digits as well, but a nonce can only be numbers). To summarize what was just explained, a block now contains; 1) transaction data, 2) the signature of the previous block, and 3) a nonce.

Step 5 — How does this make the blockchain immutable?

As discussed previously in step 3, altering a block will unchain it from the subsequent blocks. In order for an altered block to be accepted by the rest of the network, it needs to be chained to the subsequent blocks again. See where this is going? It was previously explained that this requires every block that comes after it to get a new signature. And that signature needs to meet the requirements! Giving all of these blocks a new signature will be very costly and time-consuming, although it doesn’t seem impossible.

Step 6 — How is the blockchain governed? Who determines the rules?

The Bitcoin blockchain follows a governance model of democracy, and therefore updates its’ record of transactions (and thus the Bitcoin balances) according to what the majority of its’ users say is the truth. The blockchain protocol does this automatically by always following the record of the longest blockchain that it has, because it assumes that this chain is represented by the majority. After all, it requires the majority of the computational power to create the longest version of the blockchain. This is also how an altered block is automatically rejected by the majority of the network. The majority of the network rejects an altered block automatically because it is no longer chained to the longest chain.

Final step, step 7 — Where does this leave cryptocurrencies?

Cryptocurrencies are basically an altered form of Bitcoin. Most cryptocurrencies are built upon their own blockchain protocol that may have different rules from the Bitcoin blockchain. Bitcoin is supposed to be a currency, meaning it is explicitly supposed to function as money. Monero is a cryptocurrency with the same function, but its blockchain protocol has implemented some extra rules that make it a more private currency (transactions are much harder to trace). Cryptocurrencies can however be given any kind of value, depending on their issuer. They could be referred to as ‘tokens’. These tokens can give the owners the right to ‘something’, varying from a gaming license or access to social media to downright electricity or water, you name it. Any sort of value can be attached to a ‘cryptocurrency’ token. All these cryptocurrency transactions are registered on various blockchains and can be exchanged online through cryptocurrency exchanges such as Binance. It is the new money of the internet. A good example of an industry that might be affected is the stock market industry. There is a good chance that company shares and other property rights will be registered as tokens on a blockchain in the future. But blockchains are not just limited to registering materialistic value in the form of tokens. Blockchains also have the potential to safely register data in the form of medical records, identities, history records, tax records and much, much more. This is why the technology is so huge, and I haven’t even mentioned decentralization yet (another big aspect of blockchain).