Improvements on Sun 's Conditional Access System in Pay-TV Broadcasting Systems

摘要

A conditional access system (CAS) proposed by Sun has a critical security weakness in its inability to preserve backward secrecy; a former subscriber can still access programs despite his or her change in status. This weakness in Sun 's CAS originates because 1) no change is made to a group key after a new member arrives, and 2) updates of group keys are done in an insecure manner. We show how simple protocol changes can fix these weaknesses and thus render Sun 's CAS capable of preserving backward secrecy.