The Computer Journal
Almost-Tight Identity Based Encryption Against Selective Opening Attack
Junqing Gong, Xiaolei Dong, Zhenfu Cao, Jie Chen
Abstract
The paper presents an identity based encryption (IBE) under selective opening attacks (SOA) whose security is almost-tightly related to a set of computational assumptions in composite-order bilinear groups. Our result is a combination of Bellare, Waters and Yilek's method [TCC, 2011] for constructing (not tightly) SOA secure IBE and Hofheinz, Koch and Striecks’ technique [PKC, 2015] on building almost-tightly secure IBE in the multi-ciphertext setting. In the paper, we first tune Bellare et al.’s generic construction for SOA secure IBE to show that a one-bit IBE achieving ciphertext indistinguishability under chosen plaintext attack in the multi-ciphertext setting (with one-sided public openability) tightly implies a multi-bit IBE secure under the selective opening attack. Next, we almost tightly reduce such a one-bit IBE to static assumptions in the composite-order bilinear groups employing the technique of Hofheinz et al. This yields the first SOA secure IBE with almost-tight reduction.