Disclosed are a method and system for providing cached data. The present embodiment provides a method and system for providing cached data, configured to, when it is impossible to identify a payload of a TS packet due to values scrambled as a conditional access system (CAS) is applied to a stream in a cache server, generate and provide cached data extracted for as long as a necessary section for a scrambled service stream without a descrambling process, on the basis of auxiliary information received in advance periodically or aperiodically from a set-top box or auxiliary information extracted in advance by the server itself.