SHA-256 is a cryptographic hash function that takes an input of a random size and produces an output of a fixed size. Hash functions are powerful because they are ‘one-way’. What this is means is, it is possible for anyone to use a hash function to produce an output when given an input. However, it is impossible to use the output of the hash function to reconstruct its given input. This powerful feature of the SHA-256 hash function makes it ideal for application within the Bitcoin network.