Security proof of Sakai-Kasahara's identity-based encryption scheme.

In 2003 Sakai and Kasahara proposed an identity-based encryption scheme, which has several performance advantages over existing methods. However, the scheme does not meet the standard security requirement. This work presented an efficient IBE scheme that employs a simple version of the Sakai-Kasahara scheme and the Fujisaki-Okamoto transformation. The chosen-ciphertext security of the scheme was rigorously proved in the random oracle model based on a reasonable hardness assumption. The work offers implementers an alternative to those patented protected schemes with an efficient and security proved scheme and has been used to construct other primitive such as identity-based signcryption, CL-PKEs, etc.