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Fenster schliessen

Why do we have filesystems?

Purpose of file systems:

  • Organize storage device data into files and directories/folders
  • maintain meta data (timestamps, permissions, attributes, etc.)
  • provide additional storage features (integrity, encryption, volume managemnt, quotas, etc.)
  • Create a hierarchical abstraction layer for users and programs
Fenster schliessen

Name some common filesystems and some newer filesystems.

Common files systems today:

  • FAT
  • NTFS
  • EXT4
  • HFS+

Newer filesystems:

  • BTRFS
  • APFS
  • ZFS
Fenster schliessen

What is the goal of filesystem forensics?

Why filesystem forensics is doen:

  • identify the filesystem used
  • recover files (including deletd files)
  • recover file fragments (slack, unallocated areas)
  • find attempts to hide data (change *.jpg to *.exe)
  • hash individual files for search and ignore (exclusion)
  • analyze meta data (timestamps, ownership, etc.)
  • evidence from corrupted, partially wiped filesystems
  • reconstruct past events with timelines
  • special topics: raid, journals, encryption

check what filesystems are supported by TSK (sluethkit)

fsstat -f list

Fenster schliessen

What areas are forensicly interesting on a storage drive?

Areas of forensic interest on a storage drive:

  • sector - the smalles accessible unit of a drive
  • block - consecutive sectors, smalles accessible unit on fss
  • allocated blocks - fs blocks that are allocated to files
  • unallocated blocks - fs blocks that are not allocated to files (previously allocated data may still exist)
  • inodes - meta data describing files and directories (also MFT)
  • interpartion gaps - (mmls) possible overwritten filesystems [Forensic term "slack" space]
  • volume slack - between end of filesystem and end of partition
  • file slack - between end of file and end of block
  • ram slack - between end of flile and end of sector
  • less important - 4k sectors, OSs are wiping data, TRIM

(same meaning: directories=folders, pratitions=volumes)

Fenster schliessen

What are the two ways to access a filesystem for analysis?

Via normal kernel devices:

  • raw devices (/dev/sda, /dev/mmcblk0, /dev/nvme0n1)
  • partition devices (/dev/sda1 or /dev/nvme0n1p1)

       Kernel loop devices can be created or removed from a forensic image:

  • /dev/loop*
  • $ sudo losetup -find -partscan -read-only image.dd
  • $ sudo losetup -D loop0

Via calculated offsets (be careful, check the units!):

  • byte offsets (character offsets could be 2 bytes - unicode)
  • sector offsets (sector sizen is not always 512 bytes)
  • block offsets (rememger to subract the partition sector offset)
  • use shell math: $ echo $((1024000 / 512))
Fenster schliessen

Do forensic tools require devices or images need to be mounted?

Forensic analysis tools act directly on the device, or on a forensically acquired image - no mounting needed.

Fenster schliessen

I know the drive sector, what is the filesystem block?

# echo $(((sectornumber-partitionoffset)/blocksize))

Fenster schliessen

how do can you find out if the filesystem block allocated?

# blkstat /dev/sdb1 1025