One approach to resolving this issue is to first find out who the user is, and then check which sections this user is authorized to access. Some users, in the context of certain types of resources, may find this unacceptable from the privacy point of view: they may not feel comfortable communicating who they are every time that they need to access an on-line resource!

Another approach would be to verify that the user has the appropriate credentials for accessing the resource in such a way that no other information about this user is revealed. The fact that this is at all possible may sound paradoxical. In this talk, I will explain (some of) the theory of zero-knowledge proof systems that makes this possible in principle. I will then describe my work on developing highly practical methods for authentication without identification.

This talk will be based on joint work with Jan Camenisch.