SLAMorris Final Thesis After Corrections.pdf - Cranfield University

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The information panel within the file browser is the reason for the creation of subrecords in the large directory, which enables the file to be previewed in a larger size. In Kubuntu, the image viewer Gwenview adds files to the thumbnail queue, when browsing directories in the main window of the application; however it only uses the normal thumbnail cache directory, and therefore the large directory is not modified. Within Kubuntu, it is interesting to note that there are circumstances where thumbnail subrecords are unexpectedly created. Partial subrecords within the cache are automatically generated for a selection of files in the first level subdirectories of a directory being viewed in the file browser. An example is shown in Figure 5.5, which shows the Downloads directory being viewed in the file browser. When this directory is opened, each sub-directory is represented by a series of small thumbnails, such as those shown for ‘Test Folder’. These small thumbnails represent files present in the sub-directory, and to create them, the system creates partial thumbnails of files within the sub-directory. If the subdirectory is hovered over with the mouse, the mini-thumbnails rotate through any files within the sub-directory that have thumbnail generation methods. Therefore from each first level sub-directory in a browsed folder, there may be subrecords created for up to the number of files which have thumbnail generation methods, even though the user has not browsed the sub-directory. Interestingly, partial thumbnail subrecords have two properties which allow them to be distinguished from subrecords created using standard methods. Firstly, there is a noticeable lack of metadata within the PNG, including no information on the last modified time and URI for the source file. This means there are two main methods of forming a relationship between a partial subrecord and the source file; the image stored in the subrecord and the MD5 hash of the URI Page 84
which is present in the subrecords filename. The second difference in partial subrecords is noticeable in the IDAT chunks, where upon comparison with a standard subrecord entry for the same file, it is noticeably shorter as the alpha values are missing. Figure 5-5: The directory 'Downloads' being viewed in the file browser within Kubuntu If within Kubuntu, the large thumbnail cache directory is viewed, the files within it are added to the thumbnail queue for the creation and modification of subrecords within the normal directory. These subrecords do not conform to the standard structure; instead they use the same structure as the partial subrecords. Potential thumbnail source files in Kubuntu by default are only image formats. Interestingly, thumbnails for text files are not available in the file browser. If a text file is selected within the file browser, a visual thumbnail is rendered in the information panel, but this is not stored in the cache. In both operating systems, potential source files viewed on the desktop are added to the thumbnail queue for subrecords to be added or modified in the normal directory only. However if the desktop is viewed in the file browser in Kubuntu, subrecords may also be created or modified in the large directory. Page 85
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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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Page 55 and 56: available for office documents; the
Page 57 and 58: future. It is possible to establish
Page 59: structure and syntax the user and s
Page 62 and 63: Identify existing file carving tech
Page 64 and 65: throughout this research. Within th
Page 66 and 67: corroborate the results. Time const
Page 68 and 69: 4.2.1 Legal Constraints The law can
Page 70 and 71: to the evidence and to ensure any a
Page 72 and 73: To ensure the evidence is accurate
Page 74 and 75: evidence being extracted is crucial
Page 76 and 77: analyse human behaviour, it can sti
Page 78 and 79: 4.3 Criteria for evaluating the evi
Page 80 and 81: In order to determine an artefact w
Page 83 and 84: 5 The Structure and Behaviour of th
Page 85 and 86: the way data changes. The experimen
Page 87 and 88: 5.4 Default Installations This sect
Page 89 and 90: Figure 5-3: The structure of thumbn
Page 91 and 92: these can be identified by the addi
Page 93 and 94: The tEXt chunks contain the metadat
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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: Each piece of software installed by
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
Page 126 and 127: elationship between information con
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 144 and 145: greater than the maximum size image
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
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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
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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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SLAMorris Final Thesis After Corrections.pdf - Cranfield University

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