Encryption and hashing are fundamental to the blockchain technology. In short, hashing is a one-way transformation of data to an unreadable piece of data (which is knows as the hash value). With encryption you can have a two-way transformation: You encrypt data with a certain key, so it becomes unreadable. With this key, you can always decrypt this unreadable piece of data to the original value.

What this means is that all transactions on a blockchain are immutable. You cannot change these transactions once they are recorded on a blockchain. You cannot delete this data, since that would ‘break the chain’ in a sense, rendering the complete blockchain useless.