If we want to chain several pieces of information in a way that would make any attempt to modify any of the in-betweens impossible (or at least very noticeable), there’s a neat math trick we can use called *hashing*.

Hashing is a mathemagical way to produce a number (or a string of characters) that is derived from another data, and could ** only** come from that piece of data. We can use that for our line of post-it notes with transactions.

For example, a very simplified version of hashing would be to use the formula “+2”. If we have the number 1, and we apply the hashing +2, we get 3. In this case, 3 would be the hash of 1. It sound simple (hopefully) but then anyone that knows the three pieces of information (the input, the hashing formula, and the result), can verify that 1 is the real number we hashed, and not 5 for example. The hash of 5 using our +2 formula would be 7, not 3.

We are going to use hashing in a way or another a lot while creating our cryptocurrency, because they’re very useful. And the first way we’re going to use them is to link our blocks together.