Retrieving Original User ID From Its Pseudonym

Grettings, Matomo comunity,

We are really satisfied with Matomo and considering to use it in our projects. Therefore, there is a demand from our Chief Architect that is the possibility of retrieve the original User ID from its pseudonym for on-call purposes.

We are checking the following link At the “Replace User ID with a pseudonym” section, there is a information that says “The original User ID could still be identified if certain additional information is available (which only Matomo and your data processor has access to)”. Someone knows more detailed information about the process to retrieve the original User ID from its pseudonym?

Best Regards,
Lucas Moretto Rodrigues.

Hi @lmoretto
You can identify a user for example if you know that he visited some pages and/or performed some action at a certain date/time, then search in the visit logs, and get his pseudonymized ID.
As the pseudonymized ID is a kind of hash (with secret salt), then there is no other solution to find him, except if you know the salt and hash algorithm…