Forward-Secure Hierarchical IBE with Applications to Broadcast Encryption

A forward-secure encryption scheme protects secret keys fr om exposure by evolving the keys with time. Forward security has several unique requirements in hierarchical identity-based encryption (HIBE) scheme: (1 ) users join dynamically; (2) encryption is joining-time-oblivious; (3) users evolv e secret keys autonomously. We define and construct a scalable pairing-based forward-se cure HIBE (fsHIBE) scheme satisfying all of the above requirements. We al so show how our fs-HIBE scheme can be used to realize a forward-secure publi c-key broadcast encryption scheme, which protects the secrecy of prior transm is ions in the broadcast encryption setting. We further generalize fs-HIBE into a co llusion-resistant multiple hierarchical ID-based encryption scheme, which can be u sed for secure communications with entities having multiple roles in role-ba sed access control. The security of our schemes is based on the bilinear Diffie-Hellm an assumption in the random oracle model.