Pseudonymisation

Pseudonymisation means replacing people’s identification data (such as name and surname) with meaningless identifiers - pseudonyms (e.g. numbers). The goal is to protect sensitive personal data by means of hiding the identities so to make it impossible to match the data with specific people. This way, the identities are replaced by substitute numbers - pseudonyms. A file that enables the data to be matched with specific people is separated from the sensitive data file. Therefore, only those who have both files can correctly match sensitive data with people.

Unlike anonymization, pseudonymization is a reversible process, i.e. it is possible to reconstruct the original file (to do so, it is necessary to have both its “halves” available).

What is the use of pseudonymization?

Pseudonymization is mainly used for personal data protection but can be used to protect any confidential information. By making it impossible to assign the data, e.g. medical records, to a specific person, is this information protected against both voluntary and involuntary publication by either authorised or unauthorised people.

What are the methods of pseudonymization?

One solution is to divide the data into two files, one of which contains only sensitive data and the other only their identification data. They are linked to each other by an identifier (typically a number) that can be used to put the two halves together. Another solution is to hide identification data by encryption so that only persons with the appropriate key can access it. The key is again separate from the pseudonymized file with sensitive data.