Book excerpt: This text provides the background material used for a one-week tutorial given in May/June 2000 in Portoroz, Slovenia. It is a collection of articles covering a wide area of security in networking, including: basic cryptography; public key infrastructures; security mechanisms; virtual private networks and active agents related security services; security application such as secure e-mail or secure World Wide Web; security provision in e-business and e-commerce; security service provision and trusted third party technology in banking associations; electronic money and smart card technology for e-business; and the legal aspects of electronic signatures.