Part I of this book consists of two introductory chapters. Chapter 1 provides a high-level introduction to XML and the standards specifying it, and explains why someone would want to "secure" XML. Chapter 2 provides a general introduction to digital cryptography. If you are generally familiar with both XML and digital cryptography, you can skim these two chapters.
Part II covers XML basics in great depth but has very little discussion of XML Security.
Building on the earlier chapters, Part III covers authentication, including digital signatures, message authentication codes, and canonicalization.
Part IV discusses keying and the format of keying information for both XML authentication and confidentiality.
Part V goes into XML encryption, which is the way to obtain confidentiality, and considers issues that arise in combining authentication and confidentiality.
Finally, Part VI describes all of the algorithms, both cryptographic and non-cryptographic, that can be invoked by well-known names that are specified in the XML Security standards and related documents.