In the summer of 1981 Allen Gersho organized the first major open co,ifcrcncc c~ci devoted to cryptologic research This meeting, Crypto ‘81, was held at the Universitc nl California campus in Santa Barbara Since then the Crypto’ conference has become dii annual event These are the proceedings of the fifth1 of these confercnces, Crypt0 XS Each section of this volume corresponds to a session at the meeting. Thr paperk were accepted by the program committee, sometimes on the basis of an abstract only. and appear here without having been otherwise refereed. The last section contains papers lor some of the impromptu talks given at the traditional rump session. Each of thew pq1ci-k was refereed by a single member of the program committee. An author index;is wcll;I\ ‘I keyword index, the entries for which were mainly supplied by the authors. appear at 11ic end of the volume. Unfortunately, two of the papers accepted for presentation at Crypto '85 could noi be included in this book they are: Unique Extrapolation of Polynomial Recurrences J. C. Lagarias and J. A. Reeds (A. T. & T Bell Labs) Some Cryptographic Applications of Permutation I'olynomials and Permutation Functions Rupert Nobarer (Universitat fur Bildungswissenschaftttn, Austria) It is my great pleasure to acknowledge the efforts of all of those who contributed to making these proceedings possible: the authors, program committee, other orgmizrrs ot the meeting, IACR officers and directors. and aU the attendees.