: This paper describes a concept and a method of effectively applying information-theoretic cryptography to real-time system communications. Information-theoretic security, also known as unconditional security, is independent of the computing power or time an opponent can bring to bear. These properties are suitable for power systems which require both few computational resources and long life time. This paper shows some case studies to apply this scheme into several electrical power system applications, the experimental results and the examinations of key management also.