I purchased this book because it was recommended on PJ Cameron’s notes on computational complexity. And despite of a short 20 pages Introduction to the subject, that chapter alone makes the book worth buying. This book is very well written, short and easily readable, spanning information theory, error correcting codes, cryptography and computational complexity in less than 250 pages and providing several technical details. The content is a little bit dated, but it’s more than enough for an introductory book.