Identity-based hierarchical strongly key-insulated encryption and its application

In this paper, we discuss non-interactive updating of decryption keys in identity-based encryption (IBE). In practice, key revocation is a necessary and inevitable process and IBE is no exception when it comes to having to manage revocation of decryption keys without losing its merits in efficiency. Our main contribution of this paper is to propose novel constructions of IBE where a decryption key can be renewed without having to make changes to its public key, i.e. user's identity. We achieve this by extending the hierarchical IBE (HIBE). Regarding security, we address semantic security against adaptive chosen ciphertext attacks for a very strong attack environment that models all possible types of key exposures in the random oracle model. In addition to this, we show method of constructing a partially collusion resistant HIBE from arbitrary IBE in the random oracle model. By combining both results, we can construct an IBE with non-interactive key update from only an arbitrary IBE.