SLAMorris Final Thesis After Corrections.pdf - Cranfield University

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In Chapter 9.5 a decision was taken to present the analyst with all valid image reconstructions. The file system information relating to fragments in unallocated space may not be available; this can make forming relationships between fragments difficult. There may be multiple versions of the thumbnail cache and subrecords relating to individual files which may lead to a file fragment reassembly which appears valid but was not an actual file on the device. This led to the decision to present the analyst with all valid image reconstructions; allowing the analyst to review the logs showing the reasoning which led to each reconstructed images. The analyst can then verify the information and make their own decision about what artefacts to present in their report. 11.8 Conclusion In conclusion, this research has taken a large research question and logically broken it down into smaller research goals with the aim of supporting or disproving the central hypothesis. This has been achieved by creating a set of criteria in order to evaluate the evidential value of thumbnail cache artefacts; the criteria were developed by evaluating the potential constraints on digital evidence and applying this information to the thumbnail cache. The development of the criteria before performing further investigation ensured that the criteria were independent of the results of this research. This research has described both the structure and behaviour of several popular implementations of the thumbnail cache; this research could have been improved by further investigation into the thumbs.db format. This research compared a variety of commonly implemented file fragment identification techniques; identification methods independently attempted to identify file fragments based solely on their content. Reassembly methods were based on the structural and behavioural research performed as this was deemed the most suitable method for Forensic Computing. Further research Page 288
into both identification and reassembly of image-only thumbnail cache file fragments may further refine the methodologies produced and decrease processing time. <strong>Final</strong>ly since there is no standard implementation of a thumbnail cache the methodologies created in this research were kept as general as possible; this means the research can easily be generalised to other file types to improve identification and reassembly of their file fragments. Page 289
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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
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9 Thumbnail cache fragment reassemb
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Once the fragments have been identi
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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
Page 267 and 268: then stored and marked as a complet
Page 269 and 270: Once a start of file fragment has b
Page 271 and 272: number of fragments which contain o
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
Page 285 and 286: which substantially reduces the inf
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
Page 293 and 294: adapted to extract artefact from ot
Page 295 and 296: 10.7 Discussion Both live system an
Page 297: 10.8 Conclusion This chapter evalua
Page 300 and 301: Figure 11-1: A breakdown of aim of
Page 302 and 303: analysing the file type it is possi
Page 304 and 305: singular file fragment; by combinin
Page 306 and 307: processing time of the reassembly m
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 | 339
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SLAMorris Final Thesis After Corrections.pdf - Cranfield University

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