Paper 2019/1485

Implementation of a Strongly Robust Identity-Based Encryption Scheme over Type-3 Pairings

Hiroshi Okano and Keita Emura and Takuya Ishibashi and Toshihiro Ohigashi and Tatsuya Suzuki

Abstract

Identity-based encryption (IBE) is a powerful mechanism for maintaining security. However, systems based on IBE are unpopular when compared with those of the public-key encryption (PKE). In our opinion, one of the reasons is a gap between theory and practice. For example, a generic transformation of weakly/strongly robust IBE from any IBE has been proposed by Abdalla et al., no robust IBE scheme is explicitly given. This means that, theoretically, anyone can construct a weakly/strongly robust IBE scheme by employing this transformation. However, this seems not easily applicable to non-cryptographers. In this paper, we first introduce the Gentry IBE scheme constructed over Type-3 pairings by employing the transformation proposed by Abe et al., and second we explicitly give strongly/weakly robust Gentry IBE schemes by employing the Abdalla et al. transformation. Finally, we show its implementation result and show that we can add strong robustness to the Gentry IBE scheme with a very few additional costs. We employ the mcl library to support a Barreto-Naehrig curve defined over the 462-bit prime. The encryption requires about 5 ms, whereas the decryption requires about 9 ms.

Note: An extended abstract appears in the Seventh International Symposium on Computing and Networking (CANDAR 2019). After publishing the conference version, the mcl library v1.00 (released on September 30, 2019) supports functions for computing multi-scalar multiplications (mclBnG1_mulVec, mclBnG2_mulVec, and mclBnGT_powVec) that were not employed in our implementation. In this version, we employ these functions and re-implement IBE schemes (Section 5). In addition to this, we found that our previous encodings do not work well (See Appendix), and thus we employ the KEM/DEM framework. Moreover, we add an application of robust IBEs to searchable encryption (Section 6).