Conditional Identity-based Broadcast Proxy Re-Encryption And Its Application To Cloud Email

In recent years, more and more enterprises provide cloud data sharing service, but security issues on data sharing about these applications is still not be solved perfectly, proxy re-encryption has become one of the core solution ideas. In order to adapt flexible cloud data sharing scenarios, many extension schemes based on proxy re-encryption has been pulled out. For example conditional proxy re-encryption, identity based proxy re-encryption, broadcast proxy re-encryption etc.On the basis of previous studies, this study define Conditional Identity-based Broadcast Proxy Re-encryption(CIBPRE) and its semantic security formally, Specifically, CIBPRE allows a sender to encrypt a message to multiple receivers by specifying these receivers' identities, and the sender can delegate a re-encryption key to a proxy so that he can convert the initial ciphertext into a new one to a new set of intended receivers. In terms of efficiency, the ciphertext of CIBPRE is in constant size, thus greatly reduce the cost on communication.Accomplish an instantiation of CIBPRE based on bilinear map, prove semantic security of CIBPRE in random oracle model based DBDH assumption. Experiments has been done compared CIBPRE with the existing optimal solution, and explain CIBPRE has more advantages on performance and efficiency. Finally, we show an application of CIBPRE to secure cloud email system advantageous over existing secure email systems.Compared to traditional techniques PGP(Pretty Good Privacy) and identity-based encryption, secure cloud email system based on CIBPRE achieve group send and forward on encrypted mails, and can ensure that the content of mails not be leaked to the cloud, it has great value on application.