For a rigorous, yet accessible and rather in-depth introduction to modern, provable cryptography I would recommend "Introduction to Modern Cryptography" by Kat

For a rigorous, yet accessible and rather in-depth introduction to modern, provable cryptography I would recommend "Introduction to Modern Cryptography" by Katz & Lindell. It starts from the basics, the proofs are thoroughly elaborated and it has an appendix covering the necessary math prerequisites.