The storage, routing and transmission of information, either in the form of digital data or of analog signals, plays a central role in modern society. To ensure that such information is protected from access by unauthorized persons is an important new challenge. The development of the theory and practical techniques needed to meet this challenge is the goal of current cryptological research. This research is highly varied and multidisciplinary. It is concerned with fundamental problems in mathematics and theoretical computer science as well as with the engineering aspects of complex information systems. Cryptology today ranks among the most active and interesting areas of research in both science and engineering. EUROCRYPT '85 maintained the tradition of the three previous workshops in this series (Paris 1984, Udine 1983, Burg Feuerstein 1982) with its emphasis on recent developments in cryptology, but also made a concerted effort to encompass more traditional topics in cryptology such as shift register theory and system theory. The many papers on these topics in this volume are witness to the success of this effort.