This chapter introduces the Grid Security Infrastructure, the basis for GT3's Security layer. A working knowledge of fundamental security concepts is assumed in this section. If you've read the previous section (Fundamental Security Concepts), you should be fine. If you haven't, but you know how public-key cryptography, certificates, and certificate authorities work, then you should also be fine. If neither of these apply to you, then I strongly suggest you take a look at the Fundamental Security Concepts chapter.