When someone says that they “own” a certain number of bitcoins, what that means is that they are capable of signing a valid transaction that sends that number of bitcoins to someone else. Let’s take a closer look at how that actually works. A bitcoin transaction has inputs and outputs. A new transaction identifies the outputs of previous transactions, which serve as the new transaction’s inputs. Outputs are “locked” with a script made up of data and opcodes. In order to spend an output, the spending transaction supplies an “unlocking” script that is concatenated to the output script and evaluated according to ... (full story)