Revolutionary developments which took place in the previous decade have transformed cryptography from a semi-scientific discipline to a respectable field in theoretical Computer Science. In particular, concepts such as computational indistinguishability, pseudorandomness and zero-knowledge interactive proofs were introduced, and classical notions as secure encryption and unforgeable signatures were placed on sound grounds. Our intention was to write a book that presents the basic concepts, definitions and results in cryptography. In a first burst of energy, most of the material appearing in these fragments was written, but since then very little progress has been done. Thus, I see it preferable to place these fragments in public domain rather than wait till the original plan is completed. These fragments contain a first draft for three major chapters and an introduction chapter. The three chapters are the chapters on computational difficulty (or one-way functions), pseudorandom generators and zero-knowledge. These chapters are quite complete with the exception that the zero-knowledge chapter misses the planned section on non-interactive zero-knowledge. However, none of these chapters has been carefully proofread and I expect them to be full of various mistakes ranging from spelling and grammatical mistakes to minor technical inaccuracies. I hope and believe that they are no fatal mistakes, but I cannot guarantee this either. In addition, the fragments contain an old annotated list of references (compiled mostly in February 1989). Again, I feel that something incomplete is better than nothing. This directory contains the following major files part1.ps -- a (300K) postscript file for TableOfContents and Introduction; part2.ps -- a (470K) postscript file for the chapter on One-Way Functions; part3.ps -- a (500K) postscript file for the chapter on Pseudorandomness; part4.ps -- a (800K) postscript file for the chapter on Zero-Knowledge; part5.ps -- a (265K) postscript file containing a list of references. add1.ps -- a (153K) postscript file containing additional information; Oded Goldreich Tel-Aviv, February 1995.