Identity Based Generalized Proxy Signcryption Scheme
Generalized signcryption can work as an encryption scheme, a signature scheme or a signcryption scheme with only one keypair and one algorithm. We extend it to the proxy system setting by considering sharing the same keypair and algorithm between the proxy signature and proxy signcryption, and we call it generalized proxy signcryption (GPSC). We give the 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, and with short system public parameters. Our scheme can be proved semantically secure against adaptively chosen ciphertext, chosen id and chosen warrant attack (short for IND-IB-GPSC-CCA) under the Decisional Bilinear Diffie-Hellman (DBDH) assumption, and existentially unforgeable against adaptively chosen message, chosen id and chosen warrant attack (short for EUF-IB-GPSC-CMA) under the (Computational Diffie-Hellman) CDH assumption. The performance evaluation shows it is of high efficiency. Moreover, we give a general construction of identity-based GPSC scheme from an identity-based combined signature and encryption scheme.