Guide to Computer Forensics - Chapter 6 PDF

Guide to Computer Forensics and Investigations Fourth Edition Chapter 6 Working with Windows and DOS Systems  Objectives Explain the purpose and structure of file systems Describe Microsoft file structures Explain the structure of New...

Guide to Computer Forensics and Investigations Fourth Edition Chapter 6 Working with Windows and DOS Systems  Objectives Explain the purpose and structure of file systems Describe Microsoft file structures Explain the structure of New Technology File System (NTFS) disks List some options for decrypting drives encrypted with whole disk encryption Guide to Computer Forensics and Investigations 2  Objectives (continued) Explain how the Windows Registry works Describe Microsoft startup tasks Describe MS-DOS startup tasks Guide to Computer Forensics and Investigations 3  Understanding File Systems File system – Gives OS a road map to data on a disk Type of file system an OS uses determines how data is stored on the disk A file system is usually directly related to an OS When you need to access a suspect’s computer to acquire or inspect data – You should be familiar with the computer’s platform Guide to Computer Forensics and Investigations 4  Understanding the Boot Sequence Complementary Metal Oxide Semiconductor (CMOS) – Computer stores system configuration and date and time information in the CMOS When power to the system is off Basic Input/Output System (BIOS) – Contains programs that perform input and output at the hardware level Guide to Computer Forensics and Investigations 5  Understanding the Boot Sequence (continued) Bootstrap process – Contained in ROM, tells the computer how to proceed – Displays the key or keys you press to open the CMOS setup screen CMOS should be modified to boot from a forensic floppy disk or CD Guide to Computer Forensics and Investigations 6  Understanding the Boot Sequence (continued) Guide to Computer Forensics and Investigations 7  Understanding Disk Drives Disk drives are made up of one or more platters coated with magnetic material Disk drive components – Geometry - disk’s structure of platters, tracks & sectors – Head – device that reads and writes data to a drive. 1 head per platter – Tracks – concentric circles on disk platter where data is located – Cylinders – column of tracks on 2 or more disk platters. 2 surfaces : top and bottom – Sectors – section on a track (512 bytes) Guide to Computer Forensics and Investigations 8 Guide to Computer Forensics and Investigations 9 Guide to Computer Forensics and Investigations 10 Understanding Disk Drives (continued) Properties handled at the drive’s hardware or firmware level – Zoned bit recording (ZBR)-size of sectors different – Track density-space between each track – Areal density-no of bits per square inch of platter – Head and cylinder skew Guide to Computer Forensics and Investigations 11  Solid-State Storage Devices All flash memory devices have a feature called wear-leveling – An internal firmware feature used in solid-state drives that ensures even wear of read/writes for all memory cells When dealing with solid-state devices, making a full forensic copy as soon as possible is crucial – In case you need to recover data from unallocated disk space 12  Exploring Microsoft File Structures In Microsoft file structures, sectors are grouped to form clusters – Storage allocation units of one or more sectors Clusters are typically 512, 1024, 2048, 4096, or more bytes each Combining sectors minimizes the overhead of writing or reading files to a disk Guide to Computer Forensics and Investigations 13  Exploring Microsoft File Structures (continued) Clusters are numbered sequentially starting at 0 in NTFS and 2 in FAT – First sector of all disks contains a system area, the boot record, and a file structure database OS assigns these cluster numbers, called logical addresses Sector numbers are called physical addresses Clusters and their addresses are specific to a logical disk drive, which is a disk partition Guide to Computer Forensics and Investigations 14  Disk Partitions A partition is a logical drive FAT16 does not recognize disks larger than 2 MB – Large disks have to be partitioned Windows OSs can have three primary partitions followed by an extended partition that can contain one or more logical drives Hidden partitions or voids – Large unused gaps between partitions on a disk Partition gap – Unused space between partitions Guide to Computer Forensics and Investigations 15  Disk Partitions (continued) Disk editor utility can alter information in partition table – To hide a partition Can examine a partition’s physical level with a disk editor: – Norton DiskEdit, WinHex, or Hex Workshop Analyze the key hexadecimal codes the OS uses to identify and maintain the file system Guide to Computer Forensics and Investigations 16 Guide to Computer Forensics and Investigations 17 Guide to Computer Forensics and Investigations 18  Disk Partitions (continued) Hex Workshop allows you to identify file headers – To identify file types with or without an extension Guide to Computer Forensics and Investigations 19 Guide to Computer Forensics and Investigations 20 Guide to Computer Forensics and Investigations 21  Master Boot Record On Windows and DOS computer systems – Boot disk contains a file called the Master Boot Record (MBR) Located at sector 0 of the disk drive In a hexadecimal editor, such as WinHex, you can find the first partition at offset 0x1BE – The file system’s hexadecimal code is offset 3 bytes from 0x1BE for the first partition MBR stores information about partitions on a disk and their locations, size, and other important items Several software products can modify the MBR, such as PartitionMagic’s Boot Magic Guide to Computer Forensics and Investigations 22  Examining FAT Disks File Allocation Table (FAT) – File structure database that Microsoft originally designed for floppy disks – Used before Windows NT and 2000 FAT database is typically written to a disk’s outermost track and contains: – Filenames, directory names, date and time stamps, the starting cluster number, and file attributes FAT versions – FAT12, FAT16, FAT32,VFAT and exFAT (used for mobile personal storage devices) Cluster sizes vary according to the hard disk size and file system Guide to Computer Forensics and Investigations 23  Examining FAT Disks (continued) Cluster sizes vary according to the hard disk size and file system Guide to Computer Forensics and Investigations 24  Examining FAT Disks (continued) Microsoft OSs allocate disk space for files by clusters – Results in drive slack Unused space in a cluster between the end of an active file and the end of the cluster Drive slack includes: – RAM slack and file slack An unintentional side effect of FAT16 having large clusters was that it reduced fragmentation – As cluster size increased Guide to Computer Forensics and Investigations 25  Examining FAT Disks (continued) Guide to Computer Forensics and Investigations 26  Examining FAT Disks (continued) When you run out of room for an allocated cluster – OS allocates another cluster for your file, which creates more slack space on the disk As files grow and require more disk space, assigned clusters are chained together – The chain can be broken or fragmented When the OS stores data in a FAT file system, it assigns a starting cluster position to a file – Data for the file is written to the first sector of the first assigned cluster Guide to Computer Forensics and Investigations 27  Examining FAT Disks (continued) Guide to Computer Forensics and Investigations 28  Examining FAT Disks (continued) When this first assigned cluster is filled and runs out of room – FAT assigns the next available cluster to the file If the next available cluster isn’t contiguous to the current cluster – File becomes fragmented Guide to Computer Forensics and Investigations 29  Deleting FAT Files In Microsoft OSs, when a file is deleted – Directory entry is marked as a deleted file With the HEX E5 (σ) character replacing the first letter of the filename FAT chain for that file is set to 0 Data in the file remains on the disk drive Area of the disk where the deleted file resides becomes unallocated disk space – Available to receive new data from newly created files or other files needing more space Guide to Computer Forensics and Investigations 30  Examining NTFS Disks New Technology File System (NTFS) – Introduced with Windows NT – Primary file system for Windows Vista Improvements over FAT file systems – NTFS provides more information about a file – NTFS gives more control over files and folders NTFS was Microsoft’s move toward a journaling file system It records a transaction before the system carries it out Guide to Computer Forensics and Investigations 31  Examining NTFS Disks (continued) In NTFS, everything written to the disk is considered a file On an NTFS disk – First data set is the Partition Boot Sector – Next is Master File Table (MFT) NTFS results in much less file slack space Clusters are smaller for smaller disk drives NTFS also uses Unicode – An international data format Guide to Computer Forensics and Investigations 32  Examining NTFS Disks (continued) Guide to Computer Forensics and Investigations 33  NTFS File System MFT contains information about all files on the disk – Including the system files the OS uses In the MFT, the first 15 records are reserved for system files Records in the MFT are called metadata Guide to Computer Forensics and Investigations 34  NTFS File System (continued) Guide to Computer Forensics and Investigations 35  NTFS File System (continued) Guide to Computer Forensics and Investigations 36  MFT and File Attributes In the NTFS MFT – All files and folders are stored in separate records of 1024 bytes each Each record contains file or folder information – This information is divided into record fields containing metadata A record field is referred to as an attribute ID File or folder information is typically stored in one of two ways in an MFT record: – Resident and nonresident Guide to Computer Forensics and Investigations 37  MFT and File Attributes (continued) Files larger than 512 bytes are stored outside the MFT – MFT record provides cluster addresses where the file is stored on the drive’s partition Referred to as data runs Each MFT record starts with a header identifying it as a resident or nonresident attribute Guide to Computer Forensics and Investigations 38 Guide to Computer Forensics and Investigations 39 Guide to Computer Forensics and Investigations 40 Guide to Computer Forensics and Investigations 41 Guide to Computer Forensics and Investigations 42  MFT and File Attributes (continued) When a disk is created as an NTFS file structure – OS assigns logical clusters to the entire disk partition These assigned clusters are called logical cluster numbers (LCNs) – Become the addresses that allow the MFT to link to nonresident files on the disk’s partition When data is first written to nonresident files, an LCN address is assigned to the file – This LCN becomes the file’s virtual cluster number (VCN) Guide to Computer Forensics and Investigations 43  MFT Structures for File Data For the header of all MFT records, the record fields of interest are as follows: – At offset 0x00 - the MFT record identifier FILE – At offset 0x1C to 0x1F - size of the MFT record – At offset 0x14 - length of the header (indicates where the next attribute starts) – At offset 0x32 and 0x33 - the update sequence array, which stores the last 2 bytes of the first sector of the MFT record 44  NTFS Data Streams Alternate Data streams – Ways data can be appended to existing files – Can obscure valuable evidentiary data, intentionally or by coincidence In NTFS, a data stream becomes an additional file attribute – Allows the file to be associated with different applications You can only tell whether a file has a data stream attached by examining that file’s MFT entry Guide to Computer Forensics and Investigations 45  NTFS Compressed Files NTFS provides compression similar to FAT DriveSpace 3 Under NTFS, files, folders, or entire volumes can be compressed Most computer forensics tools can uncompress and analyze compressed Windows data Guide to Computer Forensics and Investigations 46  NTFS Encrypting File System (EFS) Encrypting File System (EFS) – Introduced with Windows 2000 – Implements a public key and private key method of encrypting files, folders, or disk volumes When EFS is used in Windows Vista Business Edition or higher, XP Professional, or 2000, – A recovery certificate is generated and sent to the local Windows administrator account Users can apply EFS to files stored on their local workstations or a remote server Guide to Computer Forensics and Investigations 47  EFS Recovery Key Agent Recovery Key Agent implements the recovery certificate – Which is in the Windows administrator account Windows administrators can recover a key in two ways: through Windows or from an MS-DOS command prompt MS-DOS commands – Cipher – Copy – Efsrecvr (used to decrypt EFS files) Guide to Computer Forensics and Investigations 48  Deleting NTFS Files When a file is deleted in Windows XP, 2000, or NT – The OS renames it and moves it to the Recycle Bin Can use the Del (delete) MS-DOS command – Eliminates the file from the MFT listing in the same way FAT does Guide to Computer Forensics and Investigations 49  Resilient File System Resilient File System (ReFS) - designed to address very large data storage needs – Such as the cloud Features incorporated into ReFS’s design: – Maximized data availability – Improved data integrity – Designed for scalability ReFS uses disk structures similar to the MFT in NTFS 50 Understanding Whole Disk Encryption In recent years, there has been more concern about loss of – Personal identity information (PII) and trade secrets caused by computer theft Of particular concern is the theft of laptop computers and other handheld devices To help prevent loss of information, software vendors now provide whole disk encryption Guide to Computer Forensics and Investigations 51 Understanding Whole Disk Encryption (continued) Current whole disk encryption tools offer the following features: – Preboot authentication – Full or partial disk encryption with secure hibernation – Advanced encryption algorithms like AES and IDEA – Key management function to reset passwords – A Trusted Platform Module (TPM) microchip to generate encryption keys and authenticate logins Guide to Computer Forensics and Investigations 52 Understanding Whole Disk Encryption (continued) Whole disk encryption tools encrypt each sector of a drive separately Many of these tools encrypt the drive’s boot sector – To prevent any efforts to bypass the secured drive’s partition To examine an encrypted drive, decrypt it first – Run a vendor-specific program to decrypt the drive – Many vendors use a bootable CD or USB drive that prompts for a one-time passphrase Guide to Computer Forensics and Investigations 53  Examining Microsoft BitLocker Available only with Vista Enterprise and Ultimate editions Hardware and software requirements – A computer capable of running Windows Vista – The TPM microchip, version 1.2 or newer – A computer BIOS compliant with Trusted Computing Group (TCG) – Two NTFS partitions – The BIOS configured so that the hard drive boots first before checking other bootable peripherals Guide to Computer Forensics and Investigations 54 Examining Third-Party Disk Encryption Tools Some available third-party WDE (Whole Disk Encryption) utilities: – PGP Whole Disk Encryption – Voltage SecureDisk – Utimaco SafeGuard Easy – Jetico BestCrypt Volume Encryption – SoftWinter Sentry 2020 for Windows XP Some available open-source encryption tools: – TrueCrypt – CrossCrypt – FreeOTFE Guide to Computer Forensics and Investigations 55  Understanding the Windows Registry Registry – A database that stores hardware and software configuration information, network connections, user preferences, and setup information For investigative purposes, the Registry can contain valuable evidence To view the Registry, you can use: – Regedit (Registry Editor) program for Windows 9x systems – Regedt32 for Windows 2000, XP and Vista – Both utilities can be used for Windows 7 and 8 Guide to Computer Forensics and Investigations 56  Exploring the Organization of the Windows Registry Registry terminology: – Registry-a collection of files containing system and user information – Registry Editor – windows utility for viewing and modifying data in the registry – HKEY – windows split the registry into categories with prefix HKEY. “H” is handle for the key – Key – Each HKEY contain folders referred to as keys, Keys contain other key folders or values – Subkey – a key displayed under another key like subfolder Guide to Computer Forensics and Investigations 57  Exploring the Organization of the Windows Registry Registry terminology: – Branch – a key and its contents – Value – a name and value in a key similar to a file and its data content – Default value – all keys have a default value that may or may not contain data – Hives – specific branches in HKEY_USER and HKEY_LOCAL_MACHINE Guide to Computer Forensics and Investigations 58  Exploring the Organization of the Windows Registry (continued) Guide to Computer Forensics and Investigations 59  Exploring the Organization of the Windows Registry (continued) Guide to Computer Forensics and Investigations 60  Examining the Windows Registry Use ProDiscover Basic to extract System.dat and User.dat from an image file Guide to Computer Forensics and Investigations 61 Guide to Computer Forensics and Investigations 62  Examining the Windows Registry (continued) Guide to Computer Forensics and Investigations 63  Examining the Windows Registry (continued) Use AccessData Registry Viewer to see what information you can find in these files Guide to Computer Forensics and Investigations 64  Examining the Windows Registry (continued) Guide to Computer Forensics and Investigations 65  Examining the Windows Registry (continued) Guide to Computer Forensics and Investigations 66  Examining the Windows Registry (continued) Guide to Computer Forensics and Investigations 67  Examining the Windows Registry Tools with built-in or add-on Registry viewers: – X-Ways Forensics – OSForensics – Forensic Explorer – FTK  Summary When booting a suspect’s computer, using boot media, such as forensic boot floppies or CDs, you must ensure that disk evidence isn’t altered The Master Boot Record (MBR) stores information about partitions on a disk Microsoft used FAT12 and FAT16 on older operating systems To find a hard disk’s capacity, use the cylinders, heads, and sectors (CHS) calculation Guide to Computer Forensics and Investigations 69  Summary (continued) When files are deleted in a FAT file system, the Greek letter sigma (0xE5) is inserted in the first character of the filename in the directory New Technology File System (NTFS) is more versatile because it uses the Master File Table (MFT) to track file information In NTFS, data streams can obscure information that might have evidentiary value Guide to Computer Forensics and Investigations 70  Summary (continued) Maintain a library of older operating systems and applications NTFS can encrypt data with EFS and BitLocker NTFS can compress files, folders, or volumes Windows Registry keeps a record of attached hardware, user preferences, network connections, and installed software Guide to Computer Forensics and Investigations 71  Extra Reading Introduction to Windows Forensics https://www.youtube.com/watch?v=VYROU-ZwZX8 Guide to Computer Forensics and Investigations 72