Content and Key Management to Trace Traitors in Broadcasting Services

Abstract

Traitor tracing encryption schemes are a type of broadcasting encryption and have been developed for broadcasting services. There are multiple distinct decryption keys for each encryption key, and each service subscriber is given a unique decryption key. Any subscriber that redistributes his or her decryption key to a third party or who uses it to make a pirate receiver ($\mathcal{PR}$) can be identified using the schemes. However, almost all previous schemes are effective against only those $\mathcal{PR}$s with only one decryption key. We first discuss an attack (content comparison attack) against the above encryption schemes. The attack involves multiple distinct decryption keys and content-data comparison mechanism. We have developed a content and key management method (CKM) that makes traitor tracing schemes secure against the content comparison attack. Its use makes it impossible for $\mathcal{PR}$s to distinguish ordinary content data from test data and makes traitor tracing schemes effective against all $\mathcal{PR}$s. The CKM makes the broadcasting services secure.