**1. Introduction**

The world is living in an era of information outburst thanks to rapid speed of technological developments in computational domain. Many factors contribute to the immense amount of data available online: Mobile devices are becoming more accessible to everyone with their decreasing cost, underlying network technologies are facilitating data transfer by providing faster and more reliable communication, data processing methods (such as editing, compressing) are helping customize data format, and increasing data storage capacities are turning bulk data storage more effective.

With all technology and convenience so easily reachable, an ordinary user is allured further to handle even more information by either transferring, processing, or storing them. Yet, the issues of security and privacy are often taken for granted, and unfortunately this ignorance may cause a destructive consequence by totally violating the security and privacy of information, as well as its owner.

In this chapter, three fundamental states of information, i.e., information in transit, information in process, and information in storage, are defined first. Then the chapter addresses security and privacy of information in each state by giving examples. It should be noted that as information is the processed form of data, these two terms, i.e., information and data, are used interchangeably throughout the text. The chapter then provides algorithms to achieve privacy and security of information in these three states and how they apply to particular states of information for ensuring security.

The rest of the chapter is organized as follows: In Section 2, three states of information are defined together with examples for each. In Section 3, security mechanisms, i.e., privacy and security algorithms that apply to each state of information, are discussed in detail, and examples are provided. Finally, the chapter is concluded in Section 4.
