3. Transactions

Let's take a closer look at how Bitcoin works. We are interested in it, in particular because it is the main cryptocurrency, far more important than all the others, and because it is the best way to understand what a blockchain is, with other blockchains being merely variants of Bitcoin's, which therefore needs to be understood in detail.

When Alice wants to make a payment in bitcoins to Bernard (for example, in exchange for a book), Alice's computer will perform a series of operations. These operations are performed automatically by the software (wallet) that she has installed on her computer or smartphone, which manages communications between her machine and the Bitcoin peer-to-peer network. The software will accept or reject the transaction by checking that it complies with the protocol and, in particular, that the account being debited actually holds the bitcoins...