A Graduate Course in Applied Cryptography
And its textbook.
A beginning reader can read though the book to learn how cryptographic systems work and why they are secure. Every security theorem in the book is followed by a proof idea that explains at a high level why the scheme is secure. On a first read one can skip over the detailed proofs without losing continuity. A beginning reader may also skip over the mathematical details sections that explore nuances of certain definitions.
An advanced reader may enjoy reading the detailed proofs to learn how to do proofs in cryptography. At the end of every chapter you will find many exercises that explore additional aspects of the material covered in the chapter. Some exercises rehearse what was learned, but many exercises expand on the material and discuss topics not covered in the chapter.