Probability on Discrete Structures Book

If you've already read some of the cryptography canon (i.e. Schneier), the first three quarters or so of Modern Cryptanalysis, which, conceived as an introduction to cryptanalysis for the motivated but ultimately completely uninformed layperson as the book is, are spent explaining what cryptography is and looks like (including a whole chapter on factoring and discrete logarithms), won't be new to you. The main broad cryptanalytic techniques covered'linear and differential cryptanalysis'also won't hold any significant surprises, though Swenson obviously covers the material much more thoroughly and includes actual implementations (in moderately dubious Python) and exercises.

The main thing I got out of this book that I didn't get from any of the other, older books on crypto I've read was actually his description of elliptic curve cryptography (and ~ factorisation), which I'd obviously seen mentioned but not elaborated on before. If you haven't yet read Applied or Practical Cryptography or genuinely want to be able to perform linear or differential cryptanalysis yourself, you'll probably find this book much more useful, though it's a fun read either way.
Because of its much shorter length (about 230 pages) compared to most other books worth reading on the subject, parts of it seem a lot more daunting than they are, but the whole thing is pretty well written and easy to follow.