For one-semester, undergraduate- or graduate-level courses in Cryptography, Computer Security, and Network Security. In this age of viruses and hackers, of electronic eavesdropping and electronic fraud, security is paramount. As the disciplines of cryptography and network security have matured, more practical, readily available applications to enforce network security have developed. This text provides a practical survey of both the principles and practice of cryptography and network security. First, the basic issues to be addressed by a network security capability are explored through a tutorial and survey of cryptography and network security technology. Then, the practice of network security is explored via practical applications that have been implemented and are in use today. Visit Stallings Companion Website at http://williamstallings.com/Crypto/Crypto4e.html for student and instructor resources and his Computer Science Student Resource site http://williamstallings.com/StudentSupport.html Password protected instructor resources can  be accessed here by clicking on the Resources Tab to view downloadable files. (Registration required) Supplements Include: Solutions, Power Point slides. Projects, Encryption Lab Exercises.