Cryptography Engineering Design Principles and Practical Applications: https://www.schneier.com/books/cryptography-engineering/ https://www.schneier.com/books/

Cryptography Engineering Design Principles and Practical Applications: https://www.schneier.com/books/cryptography-engineering/ https://www.schneier.com/books/cryptography-engineering/ They cover the fundamentals from a practical engineering perspective. After reading it you can then pop up a level and read specs to understand specific deployed protocols (e.g. TLS) or down a level and read the details of individual cryptographic primitives / constructions.