SLAMorris Final Thesis After Corrections.pdf - Cranfield University

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Table 8.2 shows the improved accuracy of image-only JPEG fragment recognition with an improved result of 75.5% of this category being correctly classified. The hybrid approach took the most successful method for each classification from Chapter 7 and continued to develop the approach into a single identification method [Chapter 8]. <strong>Final</strong>ly for the reassembly methods, Section 9.8 shows the results of reassembly with the lowest result for data set 2 for the thumbcache_96 file with 81.26% of available fragments correctly reassembled; the result was due to the high number of clashes on image-only fragments. The thumbcache_idx file was reassembled with 100% accuracy. 10.6 Automation “Automation is defined as a scientific process which has been implemented to minimise the interaction of an analyst.” [Chapter 4.3.2] This process has been shown to automate the identification and reassembly of thumbnail cache file fragments by implementing a selection of methods documented in Chapters 7, 8, and 9. The extraction of thumbnail cache artefacts is also automated and documented in Section 9.10. As the previous section showed both the identification and reassembly stages of this methodology have failed to maximise the data available [Sections 7.10, 8.7, and 9.8]; therefore the resulting reassembled files may not be completed and may require further work by an analyst to identify any missing fragments should they exist. In the case of a potential clash of fragments for a position in a file during reassembly an analyst would have to perform further verification by hand. The extensive log files would assist an analyst by documenting the reasoning for each potential fragment and providing the original locations of the fragments; the original locations allow an analyst to place the pieces in context. Page 274
10.7 Discussion Both live system and identified file fragments of thumbnail cache can be analysed using replicable methods which can be corroborated by an analyst either using a second tool or by hand. The clarity of the documentation affects the ability of an analyst to replicate the methodology; in this research all methods were implemented to produce detailed logs to provide reasoning for any action and to maintain a relationship between each artefact or fragment and the original data. The use of logs allows an analyst to confirm important results independently; although it would be straightforward for an analyst to replicate the results of the structural and behavioural studies conducted on live thumbnail caches, the techniques documented in Chapters 7-9 may require additional cross disciplinary knowledge. The use of an extensive logging system ensures that any action taken by any implemented process during this research can be justified and the relationship to the original data can be shown. By splitting the process of extracting thumbnail cache artefacts from unallocated space into stages (identification, reassembly, and extraction), it assists in ensuring the process has understandable consequences; the relationship to the original data can be explained clearer if the process is broken down. By ascertaining the potential behaviour which led to an artefacts current state it is necessary to establish relationships between the thumbnail cache and other artefacts on the system. The relationships provide corroboration and supplementary information about the thumbnail cache artefacts which can assist in establishing potential user behaviour and if the system was operating typically. Both the live thumbnail cache and the reassembled fragments can potentially form relationships with the related system artefacts on the live system. However the methods implemented for identifying and reassembling file fragments were specifically designed for thumbnail cache files and therefore Page 275
Page 1:
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
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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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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
Page 263 and 264: equirement for generating table siz
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
Page 275 and 276: As the number of fragments being an
Page 277 and 278: file fragment identification on sto
Page 279 and 280: Linux Category_4: The last fragment
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
Page 291 and 292: and 6. Each stage of the method has
Page 293: adapted to extract artefact from ot
Page 297: 10.8 Conclusion This chapter evalua
Page 300 and 301: Figure 11-1: A breakdown of aim of
Page 302 and 303: analysing the file type it is possi
Page 304 and 305: singular file fragment; by combinin
Page 306 and 307: processing time of the reassembly m
Page 308 and 309: In Chapter 9.5 a decision was taken
Page 311 and 312: 12 Conclusions and future work 12.1
Page 313 and 314: potential for improving the identif
Page 315: installations of the operating syst
Page 318 and 319: Carnagey, N.L., Anderson, C.A. & Bu
Page 320 and 321: Facebook, 2013. Facebook. Available
Page 322 and 323: Helix, 2011. Helix. Available at: h
Page 324 and 325: Noblett, M., Pollitt, M., Presley,
Page 326 and 327: Stone-kaplan, K., Roter, M., 2003.
Page 329: APPENDICES Cranfield University | 3
Page 332 and 333: A.1.3 Image File Header typedefstru
Page 335 and 336: Appendix B Bayesian probability tab
Page 337 and 338: B.8 Fragment contains the ASCII str
Page 339 and 340: B.15 32 byte record structure SR po
Page 341 and 342: B.19 H3 Each byte frequency is less
Page 343 and 344: 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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