The book is aimed to provide wide knowledge about security services used and deployed in networking and related applications. This book contains background material of a one-week tutorial in information security technology which was given in May/June 2000 in Portoroz, Slovenia, under the auspices of the NATO science programme. It is a collection of articles of various authors from U.S. and Europe covering a broad area of security in networking, including basic cryptography, public key infrastructures, security in networking, e.g. ATM security and IPv6 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, as well as legal aspects of electronic signatures.