Patterns — restrict
Encrypt, aggregate and decrypt at different places.
Anonymous Reputation-based Blacklisting
Get rid of troublemakers without even knowing who they are.
Attribute Based Credentials
Attribute Based Credentials (ABC) are a form of authentication mechanism that allows to flexibly and selectively authenticate different attributes about an entity without revealing additional information about the entity (zero-knowledge property).
Encryption with user-managed keys
Use encryption in such a way that the service provider cannot decrypt the user's information because the user manages the keys.
Trustworthy Privacy Plug-in
Aggregate usage records at the user side in a trustworthy manner.