This text provides a practical survey of the principles and practice of cryptography and network security. Author William Stallings assumes readers are familiar with this field and have a reasonable mathematical background. The publication is akin to a concise university text. Stallings discusses the principles and major issues involving conventional encryption, public-key encryption, network security practice and system security. He discusses classical and modern encryption techniques, and he then reviews conventional algorithms. He continues with examinations and discussions of message authentication, hash algorithms and digital signature authentication protocols. With a focus on security, he overviews authentication applications, Kerberos, X.509 directory authentication service, mail, IP Web security and system security issues. The chapters include problems and recommended reading lists.