One of the most delicate matters that must be assessed in relation to compliance with privacy protection regulations concerns storing sensitive data within a blockchain. Choosing which information to actually store within a blockchain is therefore one of the fundamental decisions that needs to be made.

The data that is published on a blockchain is in fact accessible to all the nodes participating in the network. This is true both in public blockchains, where there are no restrictions on access to the ledger, and in permissioned blockchains, although in the latter case access to data is allowed only to known and trusted counterparts.

In the next section, we will examine what data must actually be stored within a blockchain.