I bought this book as an addition to a study guide that I am following. In the guide I have the encryption section was a bit light.
This book is excellent, it gives plenty of background history on when where how and why encryption evolved. It then proceeds to go into all the current and recent, as in last 100 years or so, encryption algorithms. It discusses some of their strengths and some of their weaknesses.
The book does not get very technical as the maths behind current encryption technologies is scary to people with without a maths degree (well I think it is.). The authors simply mention some of the maths techniques used and where they do this it is at a level that someone with high school maths education should easily be able to follow. The author also makes a point though of saying that the 'technical' information is not really needed for the understanding of the rest of the book.
All in all a really good read if you are interested in encryption without blowing your mind.