The blockchain is the long list containing every coin created and every coin sent. Put it differently, how much there is and who owns what. The name blockchain is quite literal, we’re making our list in the shape of a chain of blocks. Let’s see why it’s a great idea. More than that, it’s one of the biggest ideas of recent times.

Imagine a post-it note. This note is a small yellow square paper where we want to write the transactions made in our game. We decide that the papers should be big enough so that a reasonable number of transactions fit it, but not too big, so we don’t want a lot of space wasted if there are not enough numbers to write on it. This has an interesting side effect, instead of using a single big sheet of paper where we all write more information and therefore take longer, we use a several small ones. The way, if we have a disagreement with something written on one of them, we don’t have to write the whole huge list again, we just make that post-it into a ball, throw it in the bin, and try with a new one. But the previous ones we already agreed upon are good and set.

How can we ensure an order, that one paper came after the other? In other words: how can we always tell which one is the most recent paper? How can we be sure that nobody cheated changing the content of an old post-it, and just shuffled it back into the pile?

Our post-its are the blocks of our blockchain. And to secure it we have math on our side. We can use something called hashes.

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