SLAMorris Final Thesis After Corrections.pdf - Cranfield University

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greater than the maximum size image permitted in the next smallest thumbnail cache file. Throughout the experimentation in this chapter it has been noted that image files, PDF files and directories viewed in thumbnail mode consistently add records to the thumbnail cache; however visual thumbnails are not always stored for Microsoft Office files. This may be due to the addition of a checkbox to enable the saving of a visual thumbnail in the Save as Dialog box in Microsoft Office 2007 as shown in figure 6.6. Figure 6-5: The creation of subrecords in thumbcache_1024.db When files are viewed on moveable storage devices in thumbnail mode, entries are added to the thumbnail cache if the device is indexed by the system. A series of experiments were conducted where a directory containing 100 user generated files were moved from a USB storage device to the virtual machine. In the first experiment the storage device was attached to the virtual machine and the directory was viewed using Windows Explorer, the drive was indexed by default. The directory and its contents were then moved from the USB Page 124
storage device to the User’s “My Documents” Folder using Windows Explorer; the directory’s contents were then viewed in its new location. Figure 6-6: Introduction of a save thumbnail option The results of the experiment have showed that when a file is moved from an indexed storage device to a hard disk drive,2 records are added for each potential thumbnail cache source file. The first record represents the file on the storage media, the second represents the file on the virtual machine; therefore whilst two records are created only one has a relationship with the current state of the file. The addition of two records based on the same file due to the movement between indexed media may also help with event reconstruction. A subrecord containing the drive allocation letter was also added in the thumbcache_256 file. This shows that thumbnail cache entries for portable media may be present in the thumbnail cache and may provide corroboration that a device has an association with a particular machine or user. When the Page 125
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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
Page 93 and 94: The tEXt chunks contain the metadat
Page 95 and 96: holds information about sample dept
Page 97 and 98: Start of tEXt Chunk This tEXt chunk
Page 99 and 100: 00 00 00 2074 45 58 7453 6F 66 74 @
Page 101 and 102: order to establish if the software
Page 103 and 104: Each piece of software installed by
Page 105 and 106: which is present in the subrecords
Page 107 and 108: 5.6.2 The modification of subrecord
Page 109 and 110: ascertain if unused subrecords woul
Page 111 and 112: in thumbnail view. This shows that
Page 113 and 114: 5.9.1 Metadata There are three dist
Page 115 and 116: only information which does not con
Page 117 and 118: information in the .thumbnails cach
Page 119 and 120: uses substantially more checks whic
Page 121 and 122: any manipulation to appear as stand
Page 123: highlighting the need for understan
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Page 128 and 129: document the state of a default Win
Page 130 and 131: Figure 6-1: Directory structure for
Page 132 and 133: Clone 1-8: Directories at level 0 w
Page 134 and 135: Figure 6-2: The centralised thumbna
Page 136 and 137: Start of Record 87 F7 6A 62 4B 7B C
Page 138 and 139: Start of standard thumbnail cache s
Page 140 and 141: Start of subrecord 14F8CE010 43 4D
Page 142 and 143: 6.5 Identifying the behaviour The t
Page 146 and 147: experiment was repeated with a non-
Page 148 and 149: to be shown [Douglas, 2009].Figure
Page 150 and 151: 6.5.1.2 Circumstances where informa
Page 152 and 153: thumbnail cache based solely upon t
Page 154 and 155: the cache to remove inactive record
Page 156 and 157: 6.6.1 Windows.edb The database for
Page 158 and 159: Figure 6-10: Identifying the Defaul
Page 160 and 161: thumbnail view for 30 seconds. Upon
Page 162 and 163: checks are performed on the associa
Page 164 and 165: showing a relationship between info
Page 166 and 167: The type of a file can be identifie
Page 168 and 169: The event timeline created could th
Page 170 and 171: 6.9.2 Media thumbnails In Windows 7
Page 172 and 173: the provenance of artefacts. This i
Page 174 and 175: 6.10.2 Interpretation of Results An
Page 176 and 177: however it is still possible to tam
Page 178 and 179: implementations of the thumbnail ca
Page 180 and 181: valid results only when the file is
Page 182 and 183: 7.3.1 Statistical Methods If docume
Page 184 and 185: ate for HTML and JPEG files [Veenma
Page 186 and 187: Having described current methods fo
Page 188 and 189: previous experiments or downloaded
Page 190 and 191: L2: The fragment is part of a visua
Page 192 and 193: 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
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H1:Thumbcache_idx.db file H2: Image
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Therefore this research assumes tha
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ecords and 2 partial records. The n
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equirement for generating table siz
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100% success rate, with 0% false po
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then stored and marked as a complet
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Once a start of file fragment has b
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number of fragments which contain o
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Figure 9-7: Reassembling an image b
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As the number of fragments being an
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file fragment identification on sto
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Linux Category_4: The last fragment
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Table 9-1: Results from reassembly
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activity. All the non-standard subr
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which substantially reduces the inf
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10 Establishing the evidential valu
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The thumbnail cache artefact extrac
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and 6. Each stage of the method has
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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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