SLAMorris Final Thesis After Corrections.pdf - Cranfield University

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6.9.2 Media thumbnails In Windows 7, multimedia (media) thumbnails have a common structure, which can be seen in figure 6.16. The film strip border on the visual thumbnail identifies the file as having a media thumbnail. The media thumbnail preview of the file can be accessed when the file is selected in the file browser (figure 6.17). As with audio thumbnails, upon selection of the file, the media thumbnail can be seen in the preview pane. If the file is deselected, the media thumbnail will cease to play; should the file be reselected, the media thumbnail can only be replayed from the beginning. An experiment was performed using a set of 10 media files copied into the current “My Documents” directory of a virtual machine. Each of the media thumbnails was accessed; the first media thumbnail was accessed for 10 seconds, with each subsequent media thumbnail adding a further 10 seconds to the access time. The results have shown that the media thumbnails are created at runtime and are therefore not store on the system. However as with audio thumbnails, the visual thumbnail is stored in the cache. Figure 6-16: The structure of a media thumbnail Page 150
Figure 6-17: The use of media thumbnails 6.10 Discussion In summary, table 6.1 provides an overview of the main user activity which leads to artefacts being generated within the thumbnail cache, based on a default installation. The table shows the actions which lead to the creation, modification, and removal of records and subrecords from within the thumbnail cache structure. The table shows both the behaviour for the standard records which are associated with visual thumbnails and the non-standard entries. As can be seen from the table a wide variety of user activity can lead to information being added or updated within the thumbnail cache; however the only actions identified during this research which led to the removal of information were the user choosing to delete the thumbnail cache either manually or through a system cleaning menu. This section discusses the potential evidential value of Windows 7 thumbnail cache artefacts. The discussion is based around the evidential strengths identified in Chapter 4; this begins with looking at the criteria for establishing Page 151
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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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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
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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
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Page 156 and 157: 6.6.1 Windows.edb The database for
Page 158 and 159: Figure 6-10: Identifying the Defaul
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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
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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
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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
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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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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