Denial-of-service attacks are one of the most severe challenges confronting the online world. This ground-breaking volume discusses a new method of countering denial-of-service attacks called hop integrity. It details a suite of protocols for providing hop integrity. In particular, each protocol in this suite is specified and verified using an abstract and formal notation, called the Secure Protocol Notation. In addition, the book presents an alternative way to achieve strong hop integrity with hard sequence numbers.