[Wat09] Dual System Encryption: Realizing Fully Secure IBE and HIBE under Simple Assumptions

Authors: Brent Waters | Venue: Crypto 2009 | Source

Abstract

We present a new methodology for proving the security of identity-based encryption (IBE) and hierarchical identity-based encryption (HIBE) schemes. Prior to this work, the only constructions of these primitives without random oracles either had large parameter sizes or relied on complex complexity assumptions. Using our new technique, called dual system encryption, we give the first constructions of IBE and HIBE that are: (1) adaptively secure (no selective-ID restriction), (2) proven in the standard model, and (3) based on simple pairing-based assumptions. In a dual system encryption proof, ciphertexts and keys can each be normal or semi-functional. Semi-functional keys and ciphertexts are useless for actual decryption, but are used in the simulation. The proof proceeds in a sequence of games in which we gradually change all keys and then the challenge ciphertext to semi-functional, at which point the adversary has no information about the plaintext.