[wolverine876]

Kudos to Brave (for this and other privacy features):

Unlinkable subscription: If you sign up for Leo Premium, you’re issued unlinkable tokens that validate your subscription when using Leo. This means that Brave can never connect your purchase details with your usage of the product, an extra step that ensures your activity is private to you and only you. The email you used to create your account is unlinkable to your day-to-day use of Leo, making this a uniquely private credentialing experience.

[quinncom]

This is very cool, and something I’d like to integrate in my own apps. Does anybody know how this works exactly, not using foreign keys?

[luke-stanley]

I could guess, an "anonymous payment credential service" could do something like this: 1. User completes payment for the paid for service, 2. To track the payment entitlement, a random, unique ID is generated by the service for the user, that is not related to any of their data. 3. This ID is saved in a database as a valid payment key. 4. The database records IDs in shuffled batches, or with semi-random fuzzy / low resolution timestamps to prevent correlation between payment time and ID generation. 5. Each ID has an entitlement limit or usage stopping point, ensuring it's only valid for the subscribed period.

Another way might be Zero-Knowledge Proofs (ZKPs), but that might be more complex. They might even use their BAT crypto stuff for this somehow, I suppose. Whatever solution, would need a fundamental solution for how to avoid correlation, I think.