This book is a very cohesive introduction to public key Cryptography. Like the previous book, this is a somewhat formal presentation, similar to what you’d find in an undergraduate course. This book also has a greater focus on the mathematics, as the title suggests. I don’t think the background required is greater, but it does require being a bit more comfortable with mathematical reasoning than the other books in this section. This book goes over the foundational assumptions underpinning public key Cryptography, from RSA, to discrete logarithms, to elliptic curves, and even a small chapter on lattices. What’s nice about this book is that it provides a good overview of the various attacks on these systems. For example, different methods for factoring,or for computing the discrete logarithm. I still sometimes use this book as a reference, when I forget the details of Pohlig-Hellman, or something like that. I’d strongly recommend this book to anyone wanting to get more seriously into Cryptography, although it might get somewhat boring for some people given its particular focus.