A series of open workshops devoted to modem cryptology began in Santa Barbara, California in 1981 and was followed in 1982 by a European counterpart in Burg Feurstein, Germany. The series has been maintained with summer meetings in Santa Barbara and spring meetings somewhere in Europe. At the 1983 meeting in Santa Barbara the International Association for Cryptologic Research was launched and it now sponsors all the meetings of the series. Following the tradition of the series, papers were invited in the form of extended abstracts and were reviewed by the programme committee, which selected those to be presented. After the meeting, full papers were produced, in some cases with impro- ments and corrections. These papers form the main part of the present volume. They are placed in the same order that they took at the meeting and under the same headings, for ease of reference by those who attended. The classification under these headings was a little arbitary, needing to fit the timing of the day‘s activities, but it makes a workable method of arrangement. Also following tradition, a “rump session’’ was held during one evening, under the effective chairmanship of John Gordon. These were short presentations and those present found them to have some real interest, therefore we have taken the unusual step of including short papers contributed by the rump session speakers at the end of this volume, with a necessarily simplified review process.