The Internet was built without much in the way of security features and we have been dealing with the effects of those design decisions ever since. Fortunately there is a well-established set of principles that can be applied to improve network security; the principle of least-privilege and defense in depth are two prominent examples. Security is a systems problem: a large collection of moving parts such as key management, encryption, integrity protection, and authentication need to be addressed in a coordinated way to provide secure communication. This book draws on real-world examples ranging from Transport Layer Security (TLS) to the security of the Internet's core infrastructure to explain how secure networks are built and how end-systems connected to the Internet can be protected. Features:Introduces principles of network security that have proven to be effective Describes the building blocks of secure systems such as encryption, message authentication codes, and key distribution Illustrates the systems approach to security using examples such as Transport Layer Security (TLS 1.3) Covers the latest developments in securing the naming and routing systems of the Internet "This book fills a vital niche: it comprehensively initiates the reader into a systems approach to reasoning about network security, in all its depth and nuance." - Brad Karp, University College London