SLAMorris Final Thesis After Corrections.pdf - Cranfield University

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corroborate the results. Time constraints will impact upon this research; therefore this research will focus primarily on three operating system thumbnail caches. <strong>Final</strong>ly this chapter provided a breakdown of the tools which will be used during this research. The next chapter focuses on the first objective of this research, defining the term evidential value. Page 46
4 Defining Evidential Value 4.1 Introduction This research aims to identify the evidential value of thumbnail cache file fragments identified in unallocated space; in order to evaluate the evidential value it is first necessary to define this term and construct a set of criteria by which thumbnail cache artefacts can be evaluated. This chapter examines the constraints on evidence which may affect the construction of criteria; this is followed by the creation of a set of criteria which will be used to evaluate the results of this research. 4.2 Evidential Constraints In an ideal world, an analyst would be able to establish the exact series of events that occurred on a computer from the first time it was switched on. Every deleted file would be recoverable and all the necessary evidence to prove or disprove a series of actions had been committed would be retrievable. However there are unavoidable constraints which may impact the evidence presented in court. This section looks at a cross section of the constraints which impact forensic investigations, and summarises their potential impact on this research. It begins with a discussion on admissibility and legal constraints, this leads into sections on evidence, reliability and procedures. The constraints identified in this section are then used to create a set of criteria for establishing the evidential value of thumbnail cache artefacts in the following section. Page 47
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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 .
Page 15 and 16: LIST OF FIGURES Figure 1-1:A breakd
Page 17 and 18: LIST OF TABLES Table 5-1: A summary
Page 21 and 22: 1 Introduction 1.1 Introduction In
Page 23 and 24: potential difficulty is the identif
Page 25 and 26: This is followed by a structural an
Page 27 and 28: Chapter 6 describes the structure a
Page 29 and 30: Chapter 11 evaluates the methodolog
Page 31 and 32: 2 Related Research 2.1 Introduction
Page 33 and 34: Generally individuals, including so
Page 35 and 36: thought to be a disciplinary offenc
Page 37 and 38: 2.2.2 Tools used in Forensic Comput
Page 39 and 40: structure and behaviour. Winhex pro
Page 41 and 42: with it are important aspects of an
Page 43 and 44: An important question for each arte
Page 45 and 46: For this research it is necessary t
Page 47 and 48: 2007], which assist in building eve
Page 49 and 50: and therefore he did not have priva
Page 51 and 52: data may be affected by the behavio
Page 53 and 54: thumbnail cache is implemented in f
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 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
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
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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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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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