A Framework for Identity-Based Encryption with Almost Tight Security

We show a framework for constructing identity-based encryption (IBE) schemes that are (almost) tightly secure in the multi-challenge and multi-instance setting. In particular, we formalize a new notion called broadcast encoding, analogously to encoding notions by Attrapadung (Eurocrypt ’14) and Wee (TCC ’14). We then show that it can be converted into such an IBE. By instantiating the framework using several encoding schemes (new or known ones), we obtain the following: • We obtain (almost) tightly secure IBE in the multi-challenge, multi-instance setting, both in composite and prime-order groups. The latter resolves the open problem posed by Hofheinz et al (PKC ’15). • We obtain the first (almost) tightly secure IBE with sub-linear size public parameters (master public keys). In particular, we can set the size of the public parameters to constant at the cost of longer ciphertexts. This gives a partial solution to the open problem posed by Chen and Wee (Crypto ’13). By ap...

• Type: Journal
• Year: 2015
• Where: ASIACRYPT
• Authors: Nuttapong Attrapadung, Goichiro Hanaoka, Shota Yamada 0001
• Keywords: ASIACRYPT 2015, Cryptology