Efficient Strictly CCA-Secure Proxy Re-Encryption Scheme

摘要

プロキシが、アリス宛の暗号文Cをボブ宛の暗号文C'に変換できるような暗号方式を、プロキシ再暗号 化方式という.最近、花岡らは、（標準モデルにおいて）厳密な意味でCCA安全なー方向プロキシ再暗号化方式を初 めて構成した.しかし、再暗号化後の暗号文のサイズが大きい.本論文では、ランダムオラクルモデルの下で、より効率的なプロキシ再暗号化方式を構成し、DBDHI仮定の下でその安全性を証明する.%In proxy re-encryption (PRE) schemes, the proxy re-encrypts a ciphertext C for Alice into C' which Bob can decrypt. Recently, Hanaoka et al. constructed the first strictly CCA-secure unidirectional PRE scheme (in the standard model).However, their scheme is inefficient because the transformed ciphertext is an encryption of many components. In this paper, we show a more efficient strictly CCA-secure unidirectional PRE scheme in the random oracle model, where the security is proved under the DBDHI assumption.