In the previous part of our blockchain technology beginner's guide we explained what a hash sum is. You can read the article here. It's worth revisiting - it might make it easier to understand today's guide, in which I will try to explain what exactly blockchain is.
Blockchain is a way of saving and storing data invented by mathematicians. To explain how it works, I will use a metaphor. Imagine that a big property developer was commissioned to build a new residential district in the suburbs of Warsaw. It's going to consist of 30 identical buildings with 30 identical apartments. This would create a gigantic chain of apartment blocks.
There is a rule that says that residents cannot move into a building until the keys to all of the apartments in the previous building are given to their owners. Before each new resident in a given building gets their apartment, they are introduced to the person who moved in to the apartment next to theirs. During the introduction the new resident takes a selfie with their neighbor. On this neighbor is holding a picture, which he took when he met another neighbor, who moved in before them. This way the newest resident will get to meet all of the people who moved into the building before them.
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- Blockchain creators used a similar model. They linked users with identical rights to create a vast, distributed network. An apartment is therefore a piece of information saved in a file of a given volume, just like every building contains a set number of apartments. The file is a block connected to others in a chain, just like buildings are connected in a neighborhood - says Andrzej Horoszczak, founder and CEO of Billon.
Each participant in a blockchain knows all the information saved in it, just like each resident knows all the residents introduced to them before. A photo taken during their first meeting with their neighbor is a hash sum that verifies whether a given person is in fact the owner of the apartment. If anybody tried to manipulate some of the information - or take over someone's apartment - the fraud will immediately be visible because the neighbors have photographs that prove the apartment belongs to somebody else. Of course, new information can be added to the blockchain, just like a new person can move into the neighborhood. But they will receive an empty apartment in a new building in a new neighborhood, because the architecture of blockchain is so designed, that no information in the previous block can be modified and new information creates a new block.
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In practice each blockchain participant has a special folder on their computer where information files are saved chronologically as hash sums. Each new information added is a new file with a hash sum added to the folders of all of the blockchain participants at the end of the chain. Everyone can look at the older files any time to see what was saved - and change it, for instance by adding a comma. But then the file will gain a new hash sum and it will be saved as a new file at the end of all of the blockchain participants’ chain.
Can a blockchain be manipulated? In theory - yes. But that would require convincing the majority (in some kinds of blockchain - all) of the network's participants to confirm something that's inconsistent with the truth. If a network consists of hundreds, thousands, or even millions of users, it's virtually unlikely to happen.
That's all for today. In the next parts of our guide you will find out, among other things, how blockchain can be used to build distributed databases.
