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Guide to Computer Forensics and Investigations, Second Edition

Guide to Computer Forensics and Investigations, Second Edition. Chapter 8 Macintosh and Linux Boot Processes and File Systems. Objectives. Understand Macintosh file structures Explore Macintosh boot tasks Examine UNIX and Linux disk structures. Objectives (continued).

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Guide to Computer Forensics and Investigations, Second Edition

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  1. Guide to Computer Forensics and Investigations, Second Edition Chapter 8 Macintosh and Linux Boot Processes and File Systems

  2. Objectives • Understand Macintosh file structures • Explore Macintosh boot tasks • Examine UNIX and Linux disk structures Guide to Computer Forensics and Investigations, 2e

  3. Objectives (continued) • Understand UNIX and Linux boot processes • Examine CD data structures • Understand other disk structures Guide to Computer Forensics and Investigations, 2e

  4. Understanding the Macintosh File Structure • Mac OS X version 10.3 • Darwin core • BSD UNIX application layer • Hierarchical File System (HFC) • Extended Format (HFC+) • File Manager and Finder • Data fork and resource fork Guide to Computer Forensics and Investigations, 2e

  5. Understanding the Macintosh File Structure (continued) Guide to Computer Forensics and Investigations, 2e

  6. Understanding Volumes • Storage medium used to store files • A volume can be all or part of a hard disk • On a floppy disk, is always the entire disk • Multiple clients per volume • Allocation and logical blocks • Logical blocks cannot exceed 512 bytes • Allocation blocks are a set of logical blocks Guide to Computer Forensics and Investigations, 2e

  7. Understanding Volumes (continued) Guide to Computer Forensics and Investigations, 2e

  8. Understanding Volumes (continued) • Two EOF descriptors • Logical EOF • Physical EOF • Clumps • Groups of contiguous allocation blocks • Reduce fragmentation Guide to Computer Forensics and Investigations, 2e

  9. Understanding Volumes (continued) Guide to Computer Forensics and Investigations, 2e

  10. Exploring Macintosh Boot Tasks • Use Open Firmware • Processor- and system-independent firmware • Older Macintosh OSs • First two logical blocks are boot blocks • Master Directory Block (MDB) or Volume Information Block (VIB) • Extents overflow file • Volume Control Block (VCB) Guide to Computer Forensics and Investigations, 2e

  11. Exploring Macintosh Boot Tasks (continued) • Volume Bitmap • Tracks used and unused blocks on a volume • Mac OS 9 uses a B*-tree file system for File Manager • Actual file data is stored on the leaf nodes • Header, index, and map nodes Guide to Computer Forensics and Investigations, 2e

  12. Using Macintosh Forensic Software • For Mac OSs earlier that Mac OS x • Expert Witness originally from ASRData, now owned by Guidance Software • Black Bag Technologies tools • Deal specifically with files Macintosh hides • PhantomSearch • For Mac OS X • Almost any UNIX/Linux forensic tool Guide to Computer Forensics and Investigations, 2e

  13. Examining UNIX and Linux Disk Structures • UNIX flavors • System 7, SGI IRIX, Sun Solaris, IBM AIX, and HP-UX • BSD, FreeBSD, OpenBSD, and NetBSD • Linux distributions • Caldera, Red Hat, SuSe, Mandrake, and Debian • Most consistent UNIX-like OSs • GNU and BSD licenses Guide to Computer Forensics and Investigations, 2e

  14. Examining UNIX and Linux Disk Structures (continued) Guide to Computer Forensics and Investigations, 2e

  15. Examining UNIX and Linux Disk Structures (continued) Guide to Computer Forensics and Investigations, 2e

  16. Examining UNIX and Linux Disk Structures (continued) • Linux file systems • Second Extended File System (Ext2fs) • Ext3fs, journaling version of Ext2fs • Employs inodes • Pointer to other inodes or blocks • Keep internal link count • Deleted inodes have count value 0 • Linux file structure • Meta-data and data Guide to Computer Forensics and Investigations, 2e

  17. Examining UNIX and Linux Disk Structures (continued) Guide to Computer Forensics and Investigations, 2e

  18. UNIX and Linux Overview • Everything is a file • Files are defined as objects • UNIX consists of four components • Boot block • Disk allocation unit of at least 512 bytes • Contains the bootstrap code • Only one Guide to Computer Forensics and Investigations, 2e

  19. UNIX and Linux Overview (continued) • Superblock • Indicates disk geometry, available space, and location of the first inode • Manages the file system • Inode blocks • First data after the superblock • Assigned to every file allocation unit • Data blocks • Where directories and files are stored Guide to Computer Forensics and Investigations, 2e

  20. UNIX and Linux Overview (continued) Guide to Computer Forensics and Investigations, 2e

  21. UNIX and Linux Overview (continued) • Bad block inode • Keeps track of disk bad sectors • Commands: badblocks, mke2fs, and E2fsck/ • Linux ls command displays information about files • Continuation inode provides more information about a file or directory Guide to Computer Forensics and Investigations, 2e

  22. UNIX and Linux Overview (continued) Guide to Computer Forensics and Investigations, 2e

  23. UNIX and Linux Overview (continued) Guide to Computer Forensics and Investigations, 2e

  24. Understanding Inodes • Link data stored in data blocks • Ext2fs and Ext3fs are improvements over Ext • Data recovery easier on Ext3fs than on Ext2fs • First inode has 13 pointers • Pointers 1 to 10 are direct pointers • Pointer 11 is an indirect pointer • Pointer 12 is a double-indirect pointer • Pointer 13 is a triple-indirect pointer Guide to Computer Forensics and Investigations, 2e

  25. Understanding Inodes (continued) Guide to Computer Forensics and Investigations, 2e

  26. Understanding Inodes (continued) Guide to Computer Forensics and Investigations, 2e

  27. Understanding UNIX and Linux Boot Processes • Instruction code in firmware is loaded into RAM • Instruction code then • Checks the hardware • Load the boot program • Boot program • Loads kernel • Transfers control to kernel Guide to Computer Forensics and Investigations, 2e

  28. Understanding UNIX and Linux Boot Processes (continued) • Kernel • Boots system on single-user mode • Runs startup scripts • Changes to multiuser mode • Identifies root directory, swap and dump files • Sets host name, time zone • Runs consistency checks on the file system and mounts partitions • Starts services Guide to Computer Forensics and Investigations, 2e

  29. Understanding Linux Loader and GRUB • Linux Loader (LILO) • Old boot manager • Can start two or more OSs • Uses configuration file lilo.conf • Grand Unified Boot Loader (GRUB) • More powerful than LILO • As LILO resides on MBR • Command line or menu driven Guide to Computer Forensics and Investigations, 2e

  30. UNIX and Linux Drives and Partition Schemes • Labeled as path starting at root (/) directory • Primary master disk • First partition is /dev/hda • Second partition is /dev/hda2 • Primary slave or secondary master or slave • First partition is /dev/hdb • SCSI controllers • /dev/sda with first partition /dev/sda1 Guide to Computer Forensics and Investigations, 2e

  31. Examining CD Data Structures • Laser burns flat areas (lands) • Lower areas are called pits • Transitions • From lands to pits have binary value 1, or on • No transition has binary value 0, or off • ISO standards • ISO 9660 for CD, CD-R, and CD-RW • ISO 13346 for DVDs Guide to Computer Forensics and Investigations, 2e

  32. Examining CD Data Structures (continued) Guide to Computer Forensics and Investigations, 2e

  33. Examining CD Data Structures (continued) Guide to Computer Forensics and Investigations, 2e

  34. Examining CD Data Structures (continued) • Frame is the unit storage • Contains 24 17-bit symbols • Frames are combined into blocks • Blocks are combined into sectors • 2352 bytes for CD-DA • 2048 bytes for CD • Constant Linear Velocity (< 12X) • Constant Angular Velocity (>= 12X) Guide to Computer Forensics and Investigations, 2e

  35. Understanding Other Disk Structures • SCSI disks • IDE/EIDE disks • RAID configurations Guide to Computer Forensics and Investigations, 2e

  36. Examining SCSI Disks • SCSI • Provides a common bus communication device • During investigation • Check if the device is internal or external • Check if card, cables, adapters, terminators, and drivers are available • Advance SCSI Programming Interface (ASPI) • Might need to adjust settings • Port numbers and terminators Guide to Computer Forensics and Investigations, 2e

  37. Examining IDE/EIDE Devices • ATA drives from ATA-33 to ATA-133 • Standard 40-pin ribbon or shielded cable • 40-pin/80-wire cable for ATA-66, 100, and 133 • CMOS identifies proper disk settings • Logical block addressing (LBA) • Enhanced CHS configurations • Can pose a problem during an investigation Guide to Computer Forensics and Investigations, 2e

  38. Examining IDE/EIDE Devices • Solutions • Disk imaging tools • Old PC • Cards and adapters • ISA SCSI card • A-Card IDE adapter • SCSI-to-IDE adapter • EISA FireWire card • FireWire-to-EIDE adapter Guide to Computer Forensics and Investigations, 2e

  39. Examining the IDE Host Protected Area • ATAPI-5 AT introduced in 1998 reserved and protected areas on IDE devices • Protected Area Run Time Interface Extension Service (PARTIES) • Contains data stored by diagnostic and restore programs • Tools • Area 51 • BIOS, XBIOS Direct Access Reporter (BXDR) Guide to Computer Forensics and Investigations, 2e

  40. Understanding RAID • RAID 0 • Provides rapid access and increased storage • Lack of redundancy • RAID 1 • Designed for data recovery • More expensive than RAID 0 • RAID 2 • Data is written to a disk on a bit level • Slower than RAID 0 Guide to Computer Forensics and Investigations, 2e

  41. Understanding RAID (continued) Guide to Computer Forensics and Investigations, 2e

  42. Understanding RAID (continued) Guide to Computer Forensics and Investigations, 2e

  43. Understanding RAID (continued) Guide to Computer Forensics and Investigations, 2e

  44. Understanding RAID (continued) • RAID 3 • Uses data stripping and dedicated parity • RAID 4 • Data is written in blocks • RAID 5 • Places parity recovery data on each disk • RAID 6 • Redundant parity on each disk Guide to Computer Forensics and Investigations, 2e

  45. Understanding RAID (continued) Guide to Computer Forensics and Investigations, 2e

  46. Summary • Macintosh uses HFS • Hierarchical structure • Mac OS file structure • Data fork and resource fork • Volume refers to any storage media • Allocation and logical blocks • Ext2fs uses inodes • Ext3fs: journaling version of Ext2fs Guide to Computer Forensics and Investigations, 2e

  47. Summary (continued) • Linux file structure • Meta-data and data • CDs and DVDs are optical media • ISO 9660 and 13346 • Other device technologies • SCSI • IDE/EIDE • RAID Guide to Computer Forensics and Investigations, 2e

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