You may be overwhelmed by the amount of information available in books. I find that the best way to learn about these is to take an online (and hopefully free) online course.
While I'm yet to come across an online networking course, I find that a seven-week-long online *free* course on Cryptography is available at http://www.udacity.com/overview/Course/cs387/CourseRev/apr2012
Meanwhile, I suggest that you regularly visit https://www.coursera.org/courses
], where you get free online courses on varied topics offered by well-known professors from Stanford, Berkeley, etc. Who knows, one day in the near future they may offer a Networking course.
Once you take such a course, reading a book will reinforce the concepts better.