Providing granted rights with anonymous certificates

The electronic media of today requires users to authenticate or provide identifying properties which is usually done with login credentials or to present digitally signed certificates. Certificates are issued by a trusted certificate authority, which knows the content of a certificate and the identity of the owner. To provide a maximum level of privacy the identity of the owner must be separated from the certificate. Neither the service shall be able to determine the identity of the owner nor shall the certificate authority track the certificate throughout its use. The certificate authority may issue certificates with a known content for a pseudonymous identity that cannot be linked to the real identity of the owner. Hence the content is to be openly signed whereas the pseudonym is signed blindly. Both items have to be interweaved to ensure that the content is valid for this pseudonym only as well as to prevent from forging a certificate. After unblinding the pseudonym the certificate can be presented for use. Now the service can validate the content and the user can prove his ownership of the pseudonym in the certificate. Even with collaboration between the service and the certificate authority it is impossible to map the presented certificate to a certain identity. Thus, our approach allows a fully anonymous use of services.