Although advances in information and communication technologies had been developing e-society systems and making every kind of activities in our society highly convenient and efficient, people cannot reap full benefits from the systems because every privacy of a person or an organization will be revealed once the data put in the systems about it are linked. Aiming at the establishment of more secure and convenient e-society systems, this book discusses elements of schemes that cope with these threats. For example, schemes developed based on these elements enable persons and organizations to delegate task executions to cloud servers without disclosing their sensitive data while protecting the execution results from malicious entities. On the other hand, cloud servers can collect fees from persons and organizations and identify dishonest persons or organizations without knowing any secret of honest entities. Persons and organizations also become able to securely and fairly exchangeinformation or physical objects through communication channels without knowing or visiting their communication partners.