Master Thesis Computer Security Thesis no: MCS-2009:3 February 2009 Data Remanence: Secure Deletion of Data in SSDs Omar Al Homaidi School of Computing Blekinge Institute of Technology Soft Center SE – 37225 RONNEBY Sweden 1 This thesis is submitted to the Department of Interaction and System Design, School of Engineering at Blekinge Institute of Technology in partial fulfillment of the requirements for the degree of Master of Science in Computer Science. The thesis is equivalent to 20 weeks of full time studies. Contact Information: Author: Omar Al Homaidi Address: Minervavägen 22B, 371 41 Karlskrona – Sweden Email: [email protected] University Advisor: Martin Boldt Department of Computing External Advisors: Fredrik Forslund, Daniel Öberg SafeIT Security AB Address: Engelbrektsgatan 7, SE- 114 32 Stockholm – Sweden Phone: +46 8 665 79 59 Department of Computing Internet : www.bth.se/tek Blekinge Institute of Technology Phone : + 46 457 38 50 00 Soft Center Fax : + 46 457 102 45 SE – 372 25 RONNEBY Sweden 2 ABSTRACT The ongoing fast pace research in hardware and software technology has resulted in memory devices efficient and faster than ever before. However, the issue of security of the contained data is rarely discussed. There is an evident capability of these devices to retain data even when it is erased. In this thesis, a study is conducted to qualitatively analyze the extent to which data deletion is important and why secure deletion should be applied. Afterwards, following the sequential exploratory procedure, this paper presents an analysis of methods used to recover the data after being deleted in addition to the techniques used to securely delete this data. Based on this study, some recommendations are made to ensure the safety of data. Keywords: SSD, Secure Erase, Flash, Data Retention, ATA, TRIM. 3 ACKNOWLEDGEMENTS I would like to heartily acknowledge my advisor Martin Boldt for continuous encouragement during the time of writing this thesis. His guidance, professional style and valuable comments and recommendations helped me to accomplish this thesis on time. To Fredrik Forslund and Daniel Öberg, who took the time and effort to support me throughout my thesis. To my family, who gave me invaluable support over the years. Your encouragement is greatly appreciated. A special thanks to my friends who supported me during writing the thesis as well as reviewing and discussing some issues. 4 CONTENTS ABSTRACT ...................................................................................................................................................... 3 ACKNOWLEDGEMENTS .............................................................................................................................. 4 CONTENTS ..................................................................................................................................................... 5 LIST OF FIGURES .......................................................................................................................................... 8 LIST OF TABLES ............................................................................................................................................ 9 INTRODUCTION ........................................................................................................................................... 10 CHAPTER 1: BACKGROUND ....................................................................................................................... 11 1.1 NOR-BASED NAND-BASED FLASH TECHNOLOGIES ................................................................................... 11 1.2 NAND FLASH BASICS ................................................................................................................................ 12 1.3 NAND FLASH CHALLENGES ....................................................................................................................... 13 1.3.1 Wear-Leveling ........................................................................................................................................ 13 1.3.2 Error Correction .................................................................................................................................... 13 1.3.3 Bad Block Management ......................................................................................................................... 13 1.3.4 Garbage Collection ............................................................................................................................... 14 1.4 SSDS .......................................................................................................................................................... 14 1.4.1 HDD Architecture and Operation ......................................................................................................... 14 1.4.2 SSD Architecture and Operation ........................................................................................................... 15 1.4.3 SSD vs. HDD ......................................................................................................................................... 16 CHAPTER 2: PROBLEM DEFINITION/GOALS .......................................................................................... 18 2.1 GOALS ........................................................................................................................................................ 18 2.2 LIMITATIONS ............................................................................................................................................... 18 CHAPTER 3: METHODOLOGY ................................................................................................................... 20 3.1 RESEARCH QUESTIONS ............................................................................................................................... 21 3.1.1 RQ1: How does SSDs retain data after deletion? .................................................................................. 21 3.1.2 RQ2: What are the security risks of data retention in SSDs? ................................................................ 21 3.1.3 RQ3: What are the existing techniques to “Security Erase” data from SSDs? ..................................... 21 3.1.4 RQ4: How could SSDs be completely erased from sensitive data? ....................................................... 21 3.2 METHODOLOGY SUMMERY ......................................................................................................................... 21 3.3 INFORMATION COLLECTION ........................................................................................................................ 22 3.4 INFORMATION ANALYSIS ............................................................................................................................ 22 3.5 CASE STUDY ............................................................................................................................................... 22 3.6 EXPERIMENTS ............................................................................................................................................. 22 3.6.1 Variable Selection .................................................................................................................................. 23 3.6.2 Experiment Design ................................................................................................................................. 23 3.6.3 Result Analysis ....................................................................................................................................... 23 CHAPTER 4: THEORETICAL WORK ......................................................................................................... 24 5 4.1 DATA REMANENCE IN SSDS ....................................................................................................................... 24 4.1.1 System-Level Remanence ....................................................................................................................... 24 4.1.2 Machine-Level Remanence .................................................................................................................... 24 4.1.3 Data Remanence Consequences ............................................................................................................ 25 4.2.1 Time ....................................................................................................................................................... 25 4.2.2 Constantly Flipping the Bits .................................................................................................................. 25 4.2.3 Software Solution ................................................................................................................................... 26 4.2.4 Encryption ............................................................................................................................................. 26 4.2.5 Media Destruction ................................................................................................................................. 26 4.2.6 TRIM command ..................................................................................................................................... 27 4.3 ATA STANDARD: SECURITY ERASE ............................................................................................................ 27 4.3.1 SanDisk SSD serial