This course is a graduate-level survey of the technologies underlying network security. The first part of the course covers the principles of private and public key cryptography and describes a number of example encryption algorithms, including DES and AES. Next, the use of encryption with hash functions for digital signatures and certificates, followed by perimeter security, including firewalls, intrusion detection systems, viruses, and worms. The last part of the course encompasses a number of secure protocols, including secure email, secure HTTP, IPSec, and virtual private networks. Topics that are part of general security but peripheral to network security are not covered, e.g., physical tamper resistance, security policies, digital rights management, and biometrics.