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In this plenary talk we present our previous works on information theoretic security consisting of three miscellaneous topics. Those topics provide some specific but interesting problems arising inherently in communication systems with security requirement. The first topics is the relay channel with confidential messages (the RCC), which provides an interesting subject discussing an interplay between the two roles of the relay as a “helper” and as an “eavesdropper”. The second topics is the broadcast channel with confidential messages (the BCC) with randomness constraints stochastic encoders. In the BCC, we study a practical problem that we have some resource constraint on “dummy random variables” used for the stochastic encoders. The third topic is our recent work on an information theoretic analysis of the Shannon cipher system under side-channel attacks. In this topics we discuss some interesting relationship between the privacy amplification and the strong converse theorem for a certain multiterminal source coding system.