Information security is playing an increasingly important role in modern society, driven especially by the uptake of the Internet for information transfer. Large amount of information is transmitted everyday through the Internet, which is often the target of malicious attacks. In certain areas, this issue is vital. For example, military departments of governments often transmit a great amount of top-secret data, which, if divulged, could become a huge threat to the public and to national security. Even in our daily life, it is also necessary to protect information. Consider e-commerce systems as an example. No one is willing to purchase anything over the Internet before being assured that all their personal and financial information will al...