You mention you store anonymised IP's "Unlike some other vendors, our anonymization process is not reversible.", what is the methodology here?
The random component prevents that. And yes, there is a trust component. You have to trust that we discard these salts after 24h. We operate in Germany in a legal framework that allows you to sue us if we mislead you. So at a certain point, technology must make place for the legal system.
Because salt is rotated every few hours, never more than 24h, we can, with sufficient probability, determine that two requests are from the same visit/session. So have indication of new/unique visit in short window. Not days, but hours.
If you were to transmit a parameter that additionally attached Personal Data (email, User ID) to that session, then that becomes identifiable and is no longer anonymous. But that is strictly AT YOUR DISCRETION. And we NEVER share it with anyone but you. You will also need to inform your guest, that you associate personal data and ask for consent. But until you do, we cannot identify anyone after the salts cycle.
We mentioned "Unlike some other vendors" because we noticed that not everyone is (or was, at the time of our research) adding a random component. Without that component, salt if you like, you cannot guess the IP, but knowing the user IP and agent, you could find their historical traffic, hence attribute the traffic to an individual.
Our solution can't do it.
This practice has been used and documented in software engineering for now.
