4. Proof of work

Let's take a look at the competition that takes place every 10 minutes between the main nodes to be designated the winner of 6.25 bitcoins.

A cryptographic hash function is a function h which, to any sequence of symbols S (e.g. numbers and letters), associates another (shorter) sequence of symbols h(S) = R, and above all, which is such that it is impossible in practice for any possible value R of the function h to find an S such that h(S) = R (practical impossibility of inversion). The value R is called the "hash" of file S, or the "fingerprint" of file S. If h is a good hash function, the h(S) values produced by someone trying various values for S are as unpredictable as if they were drawn at random with a lottery wheel. What's more, changing a single symbol of S produces a result that bears no apparent relation to the result before the change. The function used...