SLAMorris Final Thesis After Corrections.pdf - Cranfield University

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Figure 11-1: A breakdown of aim of this research into smaller research problems <strong>After</strong> the development of criteria for assessing the evidential value research was conducted into the evidential value of complete and identified fragments of thumbnail cache files; a critical evaluation of this is provided in the sections below. Figure 11.1 highlights the key words in the aim and shows how they directly relate to smaller research problems which are documented in separate chapters. 11.3 Structure and Behaviour of Complete Thumbnail Caches In order to evaluate the evidential value of thumbnail cache file fragments identified from unallocated space it was necessary to firstly research the potential evidential value of a complete thumbnail cache located in a live file system. A complete cache in a live file set is likely to provide the maximum Page 280
evidential artefacts as it has all the parts of the cache and can form relationships with other parts of the system which are also complete. The structural and behavioural study focused on thumbnail caches in Ubuntu, Kubuntu, and Windows 7. An earlier preliminary study of thumbnail cache artefacts was conducted during this research to assist in identifying potential differences between the Windows Vista and Windows 7 thumbnail cache implementations. The Windows 7 operating system also utilises the earlier thumbs.db styles of thumbnail cache; each thumbnail cache in this range was tested using the same experiments in order to ensure accurate and unbiased results. The experiments were produced to mimic typical user actions on the system; since thumbnail caches generally cache user generated files the user action involved the creation, modification and deletion of various types of user created files on various kinds of storage media. These experiments aimed to encompass the likely range of values which would occur in the thumbnail caches; however it is not possible to cover all user behaviour which may directly or indirectly affect the contents of the thumbnail cache as it is not known. It could be suggested that a wider study of potential user behaviour should have been conducted before performing the experiments; however since it is not viable to perform tests on every piece of potentially relevant software with each operating system it was necessary to limit the scope of this research to the most likely to be of interest in an investigation. Further, by analysing the real thumbnail caches in Data Set 2 alongside the experimental data, there was an opportunity to identify and explore artefacts which had not been seen in the experiments thereby furthering the structural and behavioural studies. One consideration of this research was the stage at which to investigate the internal structure of the thumbnail cache files. Identifying the structures too early may influence the experimentation in an attempt to directly influence the variables identified in the structure. By performing a set of experiments before Page 281
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CRANFIELD UNIVERSITY SARAH LOUISE A
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ABSTRACT This thesis establishes th
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ACKNOWLEDGEMENTS “And above all,
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TABLE OF CONTENTS ABSTRACT ........
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6 The structure and behaviour of th
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8.6.1 Stage 1: Preliminary Checks .
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LIST OF FIGURES Figure 1-1:A breakd
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LIST OF TABLES Table 5-1: A summary
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1 Introduction 1.1 Introduction In
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potential difficulty is the identif
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This is followed by a structural an
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Chapter 6 describes the structure a
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Chapter 11 evaluates the methodolog
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2 Related Research 2.1 Introduction
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Generally individuals, including so
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thought to be a disciplinary offenc
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2.2.2 Tools used in Forensic Comput
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structure and behaviour. Winhex pro
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with it are important aspects of an
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An important question for each arte
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For this research it is necessary t
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2007], which assist in building eve
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and therefore he did not have priva
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data may be affected by the behavio
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thumbnail cache is implemented in f
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available for office documents; the
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future. It is possible to establish
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structure and syntax the user and s
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Identify existing file carving tech
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throughout this research. Within th
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corroborate the results. Time const
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4.2.1 Legal Constraints The law can
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to the evidence and to ensure any a
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To ensure the evidence is accurate
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evidence being extracted is crucial
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analyse human behaviour, it can sti
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4.3 Criteria for evaluating the evi
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In order to determine an artefact w
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5 The Structure and Behaviour of th
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the way data changes. The experimen
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5.4 Default Installations This sect
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Figure 5-3: The structure of thumbn
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these can be identified by the addi
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The tEXt chunks contain the metadat
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holds information about sample dept
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Start of tEXt Chunk This tEXt chunk
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00 00 00 2074 45 58 7453 6F 66 74 @
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order to establish if the software
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Each piece of software installed by
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which is present in the subrecords
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5.6.2 The modification of subrecord
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ascertain if unused subrecords woul
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in thumbnail view. This shows that
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5.9.1 Metadata There are three dist
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only information which does not con
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information in the .thumbnails cach
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uses substantially more checks whic
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any manipulation to appear as stand
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highlighting the need for understan
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elationship between information con
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document the state of a default Win
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Figure 6-1: Directory structure for
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Clone 1-8: Directories at level 0 w
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Figure 6-2: The centralised thumbna
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Start of Record 87 F7 6A 62 4B 7B C
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Start of standard thumbnail cache s
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Start of subrecord 14F8CE010 43 4D
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6.5 Identifying the behaviour The t
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greater than the maximum size image
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experiment was repeated with a non-
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to be shown [Douglas, 2009].Figure
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6.5.1.2 Circumstances where informa
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thumbnail cache based solely upon t
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the cache to remove inactive record
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6.6.1 Windows.edb The database for
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Figure 6-10: Identifying the Defaul
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thumbnail view for 30 seconds. Upon
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checks are performed on the associa
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showing a relationship between info
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The type of a file can be identifie
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The event timeline created could th
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6.9.2 Media thumbnails In Windows 7
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the provenance of artefacts. This i
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6.10.2 Interpretation of Results An
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however it is still possible to tam
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implementations of the thumbnail ca
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valid results only when the file is
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7.3.1 Statistical Methods If docume
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ate for HTML and JPEG files [Veenma
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Having described current methods fo
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previous experiments or downloaded
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L2: The fragment is part of a visua
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Table 7-1: Breakdown of file fragme
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approximately half the data in Data
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Table 7-3: A list of thumbnail cach
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Figure 7-2: Classifications for thu
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7.7.2 H2 For the identification of
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Relative offset: 48 0B 09 0C 11 0F
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The Bayesian Network takes into acc
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Figure 7-3: Bayesian network for H1
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Actual Fragment Type(Percentage) 7.
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Actual Fragment Type(Percentage) Ta
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Table 7-19: Method 4 Results for th
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more suited to pattern recognition
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and 2. This is possible because the
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This chapter has successfully ident
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8.2 Problem Definition In the intro
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information to examine at the end o
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files is described on the Joint Pho
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were not from thumbnail cache files
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In order to identify potential H3 f
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Actual Fragment Type (Percentage) p
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Figure 8-3: A summary of the hybrid
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cache file fragments. The headers i
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follow the standard PNG specificati
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then be viewed by an analyst and us
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Actual Fragment Type (Percentage) T
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8.8 Discussion The end aim of Chapt
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identification method into stages l
Page 251 and 252: 9 Thumbnail cache fragment reassemb
Page 253 and 254: Once the fragments have been identi
Page 255 and 256: 9.3.2 Logging In order to maintain
Page 257 and 258: H1:Thumbcache_idx.db file H2: Image
Page 259 and 260: Therefore this research assumes tha
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Page 265 and 266: 100% success rate, with 0% false po
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Page 269 and 270: Once a start of file fragment has b
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Page 273 and 274: Figure 9-7: Reassembling an image b
Page 275 and 276: As the number of fragments being an
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Page 281 and 282: Table 9-1: Results from reassembly
Page 283 and 284: activity. All the non-standard subr
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Page 287 and 288: 10 Establishing the evidential valu
Page 289 and 290: The thumbnail cache artefact extrac
Page 291 and 292: and 6. Each stage of the method has
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Page 295 and 296: 10.7 Discussion Both live system an
Page 297: 10.8 Conclusion This chapter evalua
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Page 306 and 307: processing time of the reassembly m
Page 308 and 309: In Chapter 9.5 a decision was taken
Page 311 and 312: 12 Conclusions and future work 12.1
Page 313 and 314: potential for improving the identif
Page 315: installations of the operating syst
Page 318 and 319: Carnagey, N.L., Anderson, C.A. & Bu
Page 320 and 321: Facebook, 2013. Facebook. Available
Page 322 and 323: Helix, 2011. Helix. Available at: h
Page 324 and 325: Noblett, M., Pollitt, M., Presley,
Page 326 and 327: Stone-kaplan, K., Roter, M., 2003.
Page 329: APPENDICES Cranfield University | 3
Page 332 and 333: A.1.3 Image File Header typedefstru
Page 335 and 336: Appendix B Bayesian probability tab
Page 337 and 338: B.8 Fragment contains the ASCII str
Page 339 and 340: B.15 32 byte record structure SR po
Page 341 and 342: B.19 H3 Each byte frequency is less
Page 343 and 344: B.21 H5 Stored in valid PNG chunks
Page 345 and 346: Appendix C Peer Reviewed Publicatio
Page 347 and 348: Cranfield University | 327
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Cranfield University | 331
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