4th CCS 1997 Message from General Chairs Gruezi Mitenand! Welcome to the Fourth ACM Conference on Computer and Communications Security. This Conference continues what has already become a traditional series of successful events started back in November 1993, in Fairfax, Virginia, USA. Dorothy Denning and Raye Pyle provided critical support at the beginning. Ravi Ganesan and Ravi Sandhu skillfully and tirelessly organized the Second and Third Conferences, Fall 1994 again in Fairfax, and Spring 1996 in New Delhi, India, where we had an enthusiastic and well-attended event. For the fourth edition, we are delighted to welcome you to Zurich, Switzerland, in the heart of Europe. Europeans have always made a strong contribution to past meetings, and Europe is home to many active researchers in the field, from Ireland to Israel (admittedly stretching the geographical borders of the continent where convenient). The Conference has established a tradition of emphasizing the practical and commercial aspects of computer and communications security, and we hope to do justice to that tradition and to our predecessors by offering you another successful meeting around a rich and interesting program. New this year is the decision to offer a whole day of tutorials along two parallel tracks, one on the more basic principles of security, the other on the more practical aspects. Each track offers two half-day sessions, and attendees are of course welcome to switch tracks in the course of the day as it suits their needs. The idea behind those tutorials-beyond their obvious financial advantages-is that the world is finally coming to realize the importance of well thought-through security measures to protect today's expanding open networks, and a huge pent-up demand exists for education in the area, which we can help satisfy by enhancing general awareness of the subject. Before letting you enjoy the technical program, we would like to thank many dedicated individuals for their contributions to making this event a success: First and foremost we want to thank the chairs of the Program Committee, Li Gong and Clifford Neuman, as well as all members of the Committee and indeed all authors who submitted papers for their lion's share of what makes this Conference what it is, by providing high-quality content. Content without a venue would however not be as easy to enjoy. Our next thanks thus go to Harry Rudin, who has looked after all local arrangements in a very creative and effective way. We also thank Ravi Sandhu and Ravi Ganesan for their participation on the Steering Committee and the other Committee members and past chairs of this event for their continued support and advice in helping us maintain the spirit of the Conference while adapting its shape to the changing times. We are also indebted to Mike Reiter for the publicity he provided for the event, Tsutomu Matsumoto for handling the publication of these Proceedings, and Jacques Stern for chairing the Awards Committee. Last but not least we thank the IBM Zurich Research Laboratory for its generous sponsorship of the event. Richard Graveman Principal Consultant Bellcore, USA Phil Janson Manager, IT Solutions Dept. IBM Zurich Research Laboratory