SLAMorris Final Thesis After Corrections.pdf - Cranfield University

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then be viewed by an analyst and used by the reassembly methods implemented in the next Chapter. When a fragment is copied it is given a file header which contains metadata about the fragment. The header contains: Signature [“TCFRAG”] Individual fragment identifier [8 bytes] Path of original file [44 bytes] Relative position in file [8 bytes] Classification [4 bytes] The file signature identifies the fragment as a thumbnail cache file fragment. The individual fragment identifier is a unique number based upon the order the fragments are processed; the first fragment of a batch to be processed is given the number 1. The path of the original file and relative offset in the file allows an analyst to maintain a relationship between each fragment and the original source file. The classification holds in ASCII the classification of the fragment in the first 2 bytes; the third byte is used to store the sub-category, and the fourth byte is set to 0xFF if the fragment begins with a thumbnail cache file header. 8.7 Results This section contains the results of testing the hybrid thumbnail cache file fragment identification method against the data sets used in Chapter 7. Page 222
Actual Fragment Type (Percentage) Table 8-4: Method 5 Results for the Training Set (Half of Data Set 1) Classification of fragment by method (Percentage) H1 H2 H3 H4 H5 H6 Total H 1 No. 1609 0 0 0 0 0 1609 % 100.00 0.00 0.00 0.00 0.00 0.00 100 H 2 H 3 H 4 H 5 H 6 No. 0 384020 0 0 0 0 384020 % 0.00 100.00 0.00 0.00 0.00 0.00 100 No. 0 0 2990084 0 47781 349174 3387039 % 0.00 0. 00 88.28 0.00 1.41 10.30 100 No. 0 0 0 31693 0 0 31693 % 0.00 0.00 0.00 100.00 0.00 0.00 100 No. 0 0 140 0 26322 4753 31215 % 0.00 0.00 0.44 0.00 84.32 15.22 100 No. 0 0 8454928 1038 6563467 97793362 112812795 % 0.00 0.00 7.49 0.00 5.81 86.68 100 Page 223
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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
Page 192 and 193: Table 7-1: Breakdown of file fragme
Page 194 and 195: approximately half the data in Data
Page 196 and 197: Table 7-3: A list of thumbnail cach
Page 198 and 199: Figure 7-2: Classifications for thu
Page 200 and 201: 7.7.2 H2 For the identification of
Page 202 and 203: Relative offset: 48 0B 09 0C 11 0F
Page 204 and 205: The Bayesian Network takes into acc
Page 206 and 207: Figure 7-3: Bayesian network for H1
Page 208 and 209: Actual Fragment Type(Percentage) 7.
Page 210 and 211: Actual Fragment Type(Percentage) Ta
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
Page 228 and 229: files is described on the Joint Pho
Page 230 and 231: were not from thumbnail cache files
Page 232 and 233: In order to identify potential H3 f
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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 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 and 258: H1:Thumbcache_idx.db file H2: Image
Page 259 and 260: Therefore this research assumes tha
Page 261 and 262: ecords and 2 partial records. The n
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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
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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
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adapted to extract artefact from ot
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10.7 Discussion Both live system an
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10.8 Conclusion This chapter evalua
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Figure 11-1: A breakdown of aim of
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analysing the file type it is possi
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singular file fragment; by combinin
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processing time of the reassembly m
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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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