SLAMorris Final Thesis After Corrections.pdf - Cranfield University

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When reconstructing a jigsaw, generally the corners and outside edges are identified and reassembled first, as these have an easily identifiable characteristic; generally these pieces are easy to identify as they contain at least one straight edge (Categories 1 and 2). For a file type it is possible to identify the header based upon the identified structure and syntax. If the fragment falls into Category 1, then reassembly is complete; otherwise it is then possible to reassemble the internals of the jigsaw using the edges as a method of identifying and validating the remaining reassembly. The internal file fragments (Category 3) can then be identified in sequence and validated against the selected header; after all the internal fragments have been identified the final fragment can be added to the file (Category 4). Having considered the reassembly methods used for jigsaws a model for the reassembly of file fragments was created. The general flow chart for the reassembly model is described in figure 9.1; this figure shows the process for reassembling multiple files, given a set of file fragments identified using the methodology documented in the previous chapter. The methodology can be used to construct a program to automate the process. Whilst the generalised method shows the approach for reassembly, individual file characteristics assist with selecting and validating fragments in each of the categories. Therefore each file type requires an individual approach to the selection and validation of fragments; these individual methods are discussed in later sections [Sections 9.4-7]. 9.4 Thumbcache_idx In Chapter 6 the Windows 7 thumbnail cache structure was described; the index for the Windows 7 thumbnail cache is stored in a file named thumbcache_idx; the index file fragments were identification type H1. Using the hybrid fragment identification approach described in Chapter 8, the H1 classification was identified 100% with no false positives in any data set. Page 238
Therefore this research assumes that false positives in the H1 sub-directory are likely to be minimal; the research assumes that all fragments present in this sub-directory belong to the thumbcache_idx file type. Figure 9-1: Flow Chart for File Fragment Reassembly Page 239
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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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Page 216 and 217: Table 7-19: Method 4 Results for th
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Page 220 and 221: and 2. This is possible because the
Page 222 and 223: This chapter has successfully ident
Page 224 and 225: 8.2 Problem Definition In the intro
Page 226 and 227: information to examine at the end o
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Page 230 and 231: were not from thumbnail cache files
Page 232 and 233: In order to identify potential H3 f
Page 234 and 235: Actual Fragment Type (Percentage) p
Page 236 and 237: Figure 8-3: A summary of the hybrid
Page 238 and 239: cache file fragments. The headers i
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Page 242 and 243: then be viewed by an analyst and us
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Page 246 and 247: 8.8 Discussion The end aim of Chapt
Page 248 and 249: 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: H1:Thumbcache_idx.db file H2: Image
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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
Page 300 and 301: Figure 11-1: A breakdown of aim of
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In Chapter 9.5 a decision was taken
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12 Conclusions and future work 12.1
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potential for improving the identif
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installations of the operating syst
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Carnagey, N.L., Anderson, C.A. & Bu
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Facebook, 2013. Facebook. Available
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Helix, 2011. Helix. Available at: h
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Noblett, M., Pollitt, M., Presley,
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Stone-kaplan, K., Roter, M., 2003.
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APPENDICES Cranfield University | 3
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A.1.3 Image File Header typedefstru
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Appendix B Bayesian probability tab
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B.8 Fragment contains the ASCII str
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B.15 32 byte record structure SR po
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B.19 H3 Each byte frequency is less
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B.21 H5 Stored in valid PNG chunks
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Appendix C Peer Reviewed Publicatio
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Cranfield University | 327
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SLAMorris Final Thesis After Corrections.pdf - Cranfield University

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