I taught a 3-week course on cryptology to academically gifted high school students and I found this book to be the perfect source. It is very clear and actually quite entertaining to read. And yet, I was so happy to see that no good mathematics were sacrificed.Each chapter ends with 20 or so exercises which are doable and really help one to gain a fuller understanding of the concepts involved.I would highly recommend this book to both the lay person and the professional mathematician who are interested in an introduction to cryptology.