Abstract
Distribution environment for audio and video content has changed dramatically, such as digital broadcasting service is widespread, the bandwidth available in the Internet access has been increasing, high-density storage media, e.g. DVDs and memory cards, have become inexpensive, and the number of personal computers (PCs) and mobile terminals have been growing rapidly. According this trend, variety of security technologies is required. I introduce some of them that are used in broadcasting services and content distribution services over the network.
