Universally Composable Identity-Based Encryption

The identity-based encryption (IBE) is one of the most important primitives in cryptography, and various security notions of IBE (e.g., IND-ID-CCA2, NM-ID-CCA2, IND-sID-CPA etc.) have been introduced and the relations among them have been clarified recently. This paper, for the first time, investigate the security of IBE in the universally composable (UC) framework. This paper first defines the UC-security of IBE, i.e., we define the ideal functionality of IBE, FIBE. We then show that UC-secure IBE is equivalent to conventionally-secure (IND-ID-CCA2-secure) IBE. This paper also introduces the UC-security of weaker security notions of IBE, which correspond to IND-ID-CPA IBE and IND-sID-CCA2. We finally prove that Boneh-Franklin’s suggestion on the construction of a secure signatures from an IND-ID-CPA IBE scheme is true in the UC framework.