Identity Based Generalized Proxy Signcryption Scheme

Generalized signcryption can work as an encryption scheme, a signature scheme or a signcryption scheme with only one key pair and one algorithm. We extend it to the proxy system setting by considering sharing the same key pair and algorithm between the proxy signature and proxy signcryption, and we call it generalized proxy signcryption (GPSC). We give a formal definition and security model of GPSC in the identity-based setting by considering the whole abilities of an attacker, and propose a concrete scheme in the standard model. Our scheme is publicly verifiable, with strong security by considering insider attack, resisting proxy key exposure attack and with short system public parameters. Our scheme can be proved semantically secure against adaptively chosen ciphertext, chosen id and chosen warrant attack (IND-IB-GPSC-CCA for short) under the Decisional Bilinear Diffie-Hellman (DBDH) assumption, and existentially unforgeable against adaptively chosen message, chosen id and chosen warrant attack (EUF-IB-GPSC-CMA for short) under the Computational Diffie-Hellman (CDH) assumption. The performance evaluation shows it to be of high efficiency. Moreover, we give a general construction of identity-based GPSC scheme from an identity-based combined signature and encryption scheme.