This chapter focuses on the most fundamental security service of any operating system: authentication. Before an entity is given access to a resource on a Windows system, the operating system must validate the entity s identity and check whether it can access that particular resource. The latter process is known as authorization, and it is discussed in greater detail later in this book. The first process is known as authentication and is the topic of discussion in this and the following chapters. The primary purpose of authentication is to prove and validate an entity s identity; it answers the question: to whom or what is the system talking?

The chapter starts off with a general explanation of authentication infrastructure terminology. Then it looks at the Windows authentication architecture and more detailed Windows authentication topics such as the NTLM authentication protocol, the secondary logon feature, credential caching, and strong authentication options for Windows.