## Cryptology ePrint Archive: Report 2009/084

Simulation without the Artificial Abort: Simplified Proof and Improved Concrete Security for Waters' IBE Scheme

Mihir Bellare and Thomas Ristenpart

Abstract: Waters' variant of the Boneh-Boyen IBE scheme is attractive because of its efficency, applications, and security attributes,but suffers from a relatively complex proof with poor concrete security. This is due in part to the proof's artificial abort'' step, which has then been inherited by numerous derivative works. It has often been asked whether this step is necessary. We show that it is not, providing a new proof that eliminates this step. The new proof is not only simpler than the original one but offers better concrete security for important ranges of the parameters. As a result, one can securely use smaller groups, resulting in significant efficiency improvements.

Category / Keywords: public-key cryptography / identity-based encryption

Publication Info: To appear at Eurocrypt 2009