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Xerox University Microfilms GUDES, Ehud, 1945- THE APPLICATION OF CRYPTOGRAPHY TO DATA BASE SECURITY. The Ohio State University, Ph.D., 1976 Computer Science Xerox University Microfilms, Ann Arbor, Michigan 48106 (c) Copyright by Ehud Gudes 1976 TEE APPLICATION OF CRYPTOGRAPHY TO DATA BASE SECURITY DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Ehud Gudes The Ohio State University 1 9 7 6 Reading Committee : Approved By Prof. Jerome Rothstein Prof. Harvey S . Koch Prof. Stuart H. Zweben Prof. Douglas S . Kerr Adviser Department of Computer and Information Science ACKNOWLEDGMENTS I would like to express my gratitude to my major adviser. Professor Jerome Rothstein for accepting me as his advisee in the middle of this research, and for many contributions to this work especially in its later parts. The most important ones were first, his observation that Shannon's unicity distance is inappropriate for data base cryptography and that the work factor approach was needed, and second, his idea of using the "random key generation" method as an easy way to achieve a high work factor. Professor Rothstein’s constructive criticism and his tire­ less efforts to improve the presentation of this work are greatly appreciated. I would like to thank my former major adviser. Professor Fred Stahl of Columbia University, for introducing me to the subject of cryptography, for his help in formulating the basic problems and for directing the first half of this research. I would like to thank Professor Harvey Koch for his help and encouragement throughout this research and for his contributions to the data base model. Professor Koch's advice in difficult moments was instrumental for the com­ pletion of this work. I want to thank Professors S. Zweben and D. Kerr for serving on my reading committee and for their helpful comments and suggestions which improved the presentation of the results significantly. Thanks also go to Mark Ebersole from IRCC for providing the file used in the experiment, and to Steve Miller for his help in implementing the NBS block cipher. I also would like to thank Professor M. Yovits and the Department of Computer and Information Science for their financial sup­ port in the last three and a half years. This work is dedicated to Amiella, my wife, for her help, encouragement, understanding and endurance through­ out this long and demanding road. August 2, 1945 . Born - Haifa, Israel 1967 .......... B.Sc., Technion - IIT, Haifa, Israel 1970-1972 . System Programmer, Technion Computer Center, Haifa, Israel 1973 .......... M.Sc., Technion - IIT, Haifa, Israel 1973-1976 . Research and Teaching Associate, The Ohio State University, Columbus, Ohio PUBLICATIONS With A. Reiter, "On Evaluating Boolean Expressions", Soft­ ware Practices and Experience, December, 1973. With F. Stahl and H. Koch, "The Application of Cryptographic Transformations to Data Base Security", NCC Proceedings, 1976. FIELDS OF STUDY Major Field; Computer and Information Science Studies in System Programming. Professors J. Rothstein, S. Zweben and D. Kerr Studies in Information Storage and Retrieval. Professor H. Koch Studies in Automata Theory. Professors J. Rothstein and H. W. Buttelmann TABLE OF CONTENTS Page ACKNOWLEDGMENTS ...................................... Ü VITA.................................................... iii LIST OF TABLES........................................ vii LIST OF FIGURES...................................... viii Chapter I. INTRODUCTION AND MOTIVATION . 1 1.1 Computer Data Security .................. 1 1.2 Data Security Risks and Their Countermeasures........................ 3 1.3 The Role of Cryptography in Data Security ................ 7 1.4 The Objectives and the Organization of this Dissertation.................. 9 II. REVIEW OF CRYPTOGRAPHY 13 2.1 Traditional Cryptography ................ 13 2.2 Measures for Cryptographic Security. 17 2.3 Applying Cryptography to a Computer System........................ 19 2.4 Cryptography and Data Bases.............. 26 2.5 Summary. ............. 27 III. REVIEW OF DATA BASE SECURITY................. 28 3.1 General Data Security Mo d e l s ............ 28 3.2 Data Base Security vs. Operating System Security........................ 31 3.3 Basic Concepts in Data Base Security . 33 3.4 Analysis of Data Base M o d e l s........... 35 3.5 Cryptography and Data Bases............. 39 3.6 Summary.................................. 41 IV. A MULTI-LEVEL STRUCTURED MODEL OF DATA BASE . 42 4.1 Introduction........................... 42 Page 4.2 Four Levels Model..................... 43 4.3 Notation and Definitions............. 51 4.4 Examples of Standard Structures in the Level Notation............... 56 4.5 Discussion........................... 62 4.6 Summary. ........................ 62 V. CRYPTOGRAPHIC TRANSFORMATIONS IN THE MULTI-LEVEL MODEL ............................ 64 5.1 Basic Definitions..................... 64 5.2 Transformations Between Physical Levels .......................... 65 5.3 Using Cryptographic Transformations. 74 5.4 Summary ............................. 80 VI. DESIGN OF A SECURE FILE SYSTEM BASED ON USER CONTROLLED CRYPTOGRAPHIC TRANSFORMATIONS . 81 6.1 General System Structure............. 81 6.2 Compartmentalized, Data Independent Protection Specifications........... 88 6.3 Hierarchial Protection Specifications. 102 6.4 Data Dependent Protection Specifications . Ill 6.5 Summary................................ 116 VII. EVALUATING THE SECURITY OF FILE ENCIPHERING . 118 7.1 Introduction.......................... 118 7.2 Review of Shannon's Measures ............ 119 7.3 The File as a Message S o urce.......... 122 7.4 Combinatorial Approach to the Work Factor Measure ........................ 128 7.5 Definition of the Work Factor. ...... 146 7.6 Other Factors............... 148 7.7 Summary................................ 150 VIII. EXPERIMENTS WITH FILE ENCIPHERING.............. 152 8.1 Introduction.......................... 152 8.2 General Description of the Experiment. 153 8.3 Detailed Description of the Experiment . 158 8.4 The Results.. 16 4 8.5 Analysis of the Results................176 8.6 Summary................................ 182 Page IX. SUMMARY AND SUGGESTIONS FOR FUTURE RESEARCH.................................... 183 9.1 Summary and Main Contributions........... 183 9.2 Points for Future Research........ 185 BIBLIOGRAPHY......................................... 187 APPENDIX A .......................................... 194 LIST OF TABLES Page Table 1 CLEAR......................................... 165 2 C A E S A R....................................... 166 3 V E R N A M ...................................... 167 4 NBS....... ................................... 168 5 PRVERNAM.................................... 169 6 FHOMOPHON.1.................................. 170 7 FHOMOPHON.2.................................. 171 LIST OF FIGURES Page Figure 1 Technical Safeguard and Data Security Risks............................ 1 2 A Portion of an Access Ma t r i x............... 30 3 The Levels Approach.................. 32 4 Multiple Physical Levels..................... 44 5 Spreading Protection Specifications and Mechanisms............................ 49 6 The Connection Between the Logical Data Base Level/ the Physical Data Base Level/ the Logical Records and the Physical Records.......................... 55 7 A "Set" Structure.................. .. 57 8 Access Paths.................... 59 9 Record Splitting............................. 61 10 Types of Cryptographic Transformations. 73 11