Enhancing privacy of federated identity management protocols: anonymous credentials in WS-security

Federated Identity Management (FIM) allows for securely provisioning certified user identities and attributes to relying parties. It establishes higher security and data quality compared to user-asserted attributes and provides for stronger user privacy protection than technologies based upon user-side attribute certificates. Therefore, industry pursues the deployment of FIM solutions as one cornerstone of the WS-Security framework. Current research proposes even more powerful methods for security and privacy protection in identity management with so called anonymous credential systems. Being based on new, yet well-researched, signature schemes and cryptographic zero-knowledge proofs, these systems have the potential to improve the capabilities of FIM by superior privacy protection, user control, and multiple use of single credentials. Unfortunately, anonymous credential systems and their semantics being based upon zero-knowledge proofs are incompatible with the XML Signature Standard which is the basis for the WS-Security and most FIM frameworks. We put forth a general construction for integrating anonymous credential systems with the XML Signature Standard and FIM protocols. We apply this method to the WS-Security protocol framework and thus obtain a very flexible WS-Federation Active Requestor Profile with strong user control and superior privacy protection.