Bitcoin

Bitcoin is not trying to “issue coins.” It is trying to solve a harder problem: how can a group of mutually untrusted nodes agree on who spent what, without a central bookkeeper?

What Problem It Solves

The hard part of digital cash is not encryption. It is double-spending. If the same money can be copied and spent twice, it is no longer money, only data that can be resent.

In a centralized system, a clearing authority decides who spent first. In an open network, that authority does not exist. Nodes do not trust each other, messages may be delayed or lost, and forks may appear. At one moment, two transactions may both look valid.