## Cryptology ePrint Archive: Report 2013/505

Improvement of One Anonymous Identity-Based Encryption

Zhengjun Cao and Lihua Liu

Abstract: In 2009, Seo et al. proposed an anonymous hierarchical identity-based encryption (IBE). The ciphertext consists of $(C_1, C_2, C_3, C_4)$, where $C_1$ is the blinded message, $C_4$ is the blinded identity, both $C_2$ and $C_3$ are used as decrypting helpers. To prove its security, the authors defined five games and introduced a strong simulator who is able to select different Setups for those games. In this paper, we optimize the IBE scheme by removing one decrypting helper and the strong simulator. We show its security under the $\ell$-computational Diffie-Hellman assumption with a normal simulator who only requires a unique Setup.

Category / Keywords: cryptographic protocols / Anonymous identity-based encryption; bilinear groups of composite order; doubly randomized key; strong simulator.