Digital Forensics

Dr. Bhavani Thuraisingham

The University of Texas at Dallas

File Systems and Forensics Tools

September 20, 2013

Outline

File Systems

- File Systems Overview

- Windows File System (for Forensics) Tools and Standards

- Forensics Tools

- Standards

- Revisiting File Systems

- http://www.cftt.nist.gov/NISTIR_7490.pdf

Windows File System

Overview of File Systems Microsoft File Structures NTFS Disks (New Technology File System)

- Partitions, disks, etc. Other concepts (Registries, startup tasks) Virtual Machines

File Systems

What is it?

- Structure of the data that is stored

- Linear file system, Hierarchical file system, etc. Type of file system determines how the data is stored on disk File system is part of the OS; a file system is a way for storing

and organizing computer files and the data they contain to make it easy to find and access them.

Key aspects of file system include

- Boot sequence

- Disk drives

- File name, metadata, security access

- Different types of file systems

File Systems - 2 Boot sequence

- When a suspect’s computer starts, make sure it boots to a forensic floppy disk/CD and not to the hard disk

- Booting to the hard disk may overwrite evidence

- Make modifications to CMOS setup Disk drives

- Geometry, Head, Tracks, Cylinders, Sectors Every file has a file name; metadata consists of information

about a file, access control policies may be defined on a file Types of file systems include disk file system, flash file

systems, database file systems, network file systems, - - -

File Systems - 3 File systems typically have directories which associate file names

with files, usually by connecting the file name to an index in a file allocation table (FAT in Windows, Inode in Unix)

Directory structures may be flat, or allow hierarchies where directories may contain subdirectories.

In some file systems, file names are structured, with special syntax for filename extensions and version numbers. In others, file names are simple strings

Metadata

- The length of the data contained in a file may be stored as the number of blocks allocated for the file or as an exact byte count.

- The time that the file was last modified may be stored as the file's timestamp; also file creation time, the time it was last accessed

Microsoft File Structures

Sectors

- Sectors are groped to for clusters which are the storage allocations units.

- Cluster numbers are logical addresses and section numbers are physical addresses.

Disk Partitions Hard drive is partitioned. A partition is a logical drive. Master Boot Record (MBR)

- Stores information about the partitions in a disk and their locations, sizes etc.

FAT (File Allocation Table) Disks

- Original Microsoft file structure database NTFS

- New Technology File System

NTFS Disks

Overview of NTFS Disks

- Newer Microsoft products are based on new Technology File System

- Everything written to a disk is considered s file

- First data set is the Partition Boot Sector

- Next is the Master File Table (similar to FAT)

- Uses Unicode NTFS System Files

- The first file MFT ahs information in all the files

- Records in MFT are called metadata

NTFS Disks - 2

NTFS Data Streams

- Ways data can be appended to existing files

- Can obscure evidence; only way to know there is a data stream is by looking at MFT

NTFS Compressed Files

- Provides compression to improve data storage Encryption

- Implements public key/private key method

- Whole disk encryption (Chapter 4) for extra protection for certain information such as personal identity numbers.

Performance

- tune some of global NTFS parameters to achieve significant increase of disk performance. Other techniques like disk defragmentation could help

NTFS Disks – 3 (Summary)

File Storage Hardware and Disk Organization Hard Disk Drive Basics

- Making Tracks

- Sectors and Clusters Master Boot Record (MBR)

- Viruses Can Infect the Master Boot Record Partition Table

- Boot Indicator Field

- System ID Field

- Starting and Ending Head, Sector, and Cylinder Field

- Relative Sectors and Number of Sectors Fields

- Logical Drives and Extended Partitions

NTFS Recovery

Why id Partition recovery needed

- MBR (Master Boot Record) is damaged

- Partition is deleted or Partition Table is damaged

- Partition Boot Sector is damaged

- Missing or Corrupted System Files Partition/Drive Recovery

- "Physical partition recovery". The goal is to find out the problem and write some information to the proper place on HDD and after that partition becomes visible to OS again.

- "Virtual partition recovery". The goal is to determine the critical parameters of the deleted/damaged/overwritten partition and after that enable to scan it and display its content.

NTFS Recovery - 2

NTFS File Recovery

- Disk Scan for deleted entries Disk Scan is a process of low-level enumeration of

all entries in the Root Folders; The goal is to find and display deleted entries.

- Defining clusters chain for the deleted entry To define clusters chain scan drive, going through

one by one all allocated and free clusters belonging to the file until the file size equals to the total size of the selected clusters. If the file is fragmented, clusters chain will be composed of several extents.

- Clusters chain recovery After clusters chain is defined read and save

contents of the defined clusters to another place verifying their contents.

Other Concepts

Registry

- Registry is a database that stores initialization files such as hardware/software configuration, network connections, user preferences, setup information

- Set of tools (e.g., Registry editor) to view and modify the data

Start-up tasks

- Forensics examiner must have a very good understanding of what happens to the data during start-up.

- E.g., What is the process, what are the files involved, etc.

Virtual Machines

An examiner may need lot more space than he has on the machine he is using. The concept of Virtual machine is used it overcome this limitation.

Virtual machine addresses the need for having a variety of resources by creating the representation of another computer on an existing physical computer.

A few files from the other computer is on the examiner’s machine and space ahs to be allocated for this.

Also useful when one upgrades computer, but still has some old applications. Therefore virtual machine of the old OS is created.

Reading for Lecture for September 20th

Intelligence Digital Forensics

http://dfrws.org/2006/proceedings/7-Alink.pdf XIRAF – XML-based indexing and querying for digital forensics

http://dfrws.org/2006/proceedings/8-Turner.pdf Selective and intelligent imaging using digital evidence bags

http://dfrws.org/2006/proceedings/9-Lee.pdf Detecting false captioning using common-sense reasoning

Forensics Tools

Hardware Forensics Tools

- Range from single purpose components (e.g., devices) to complete systems (forensics workstations)

Software Forensics Tools

- Analysis tools such ProDiscover and EnCase

Functions of Forensics Tools

Acquisition Validation and Discrimination Extraction Reconstruction Reporting Comparison of some forensics tools are given on page 277 of

Textbook (ProDiscover, AccessData, EnCase)

Functions of Forensics Tools - 2

Acquisition

- Tools for data acquisition

- Physical data copy, logical data copy, data acquiring format, GUI acquisition

Validation and Discrimination

- Integrity of the data, Also includes hashing, filtering, analyzing file headers

Extraction

- Recovery task

- Data viewing, Keyword searching, Decompressing

Reconstruction Reporting

Functions of Forensics Tools - 3

Reconstruction

- Recreate the crime scene (suspect drive)

- Disk to disk copy, Image to disk copy, etc. Reporting

- Reporting generation tools help the examiner the prepare report

- Also helps to log reports

Software Tools

Command line forensics tools Unix/Linux forensics tools

- SMART, Helix, Autopsy and Sleuth Kit GUI Forensics Tools

- Visualizing the data is important to understand the data

Hardware Tools

Forensics workstations

- How to build a workstation

- What are the components

- How are the workstations connected in a lab

- How can distributed forensics be carried out Write Blockers

- Write blocker devoices to protect evidence disks (see the discussion in Chapter 4 under data acquisition)

Validating Forensics Tools

NIST (National Institute of Standards and Technology) is coming up with standards for validation (will be discussed under standards)

- Establish categories for forensics tools, Identify forensics category requirements, Develop test assertions

- Identify test cases

- Establish test method

- Report test results

- NIST (National Institute of Standards and Technology) is coming up with standards for validation (will be discussed under standards

Chapter 7 discusses validation protocols as well as some examination protocols

NIST Standards

There are three digital forensics projects at the National Institute of Standards and Technology (NIST).

These projects are supported by the U.S. Department of Justice's National Institute of Justice (NIJ), federal, state, and local law enforcement, and the National Institute of Standards and Technology Office of Law Enforcement Standards (OLES) to promote efficient and effective use of computer technology in the investigation of crimes involving computers.

These projects are the following:

- • National Software Reference Library (NSRL)

- • Computer Forensic Tool Testing (CFTT)

- • Computer Forensic Reference Data Sets (CFReDS)

NSRL

The NSRL is designed to collect software from various sources and incorporate file profiles computed from this software into a Reference Data Set (RDS) including hashes of known files created when software is installed on a computer. The law enforcement community approached NIST requesting a software library and signature database that meets four criteria:

- • The organizations involved in the implementation of the file profiles must be unbiased and neutral.

- • Control over the quality of data provided by the database must be maintained.

- • A repository of original software must be made available from which data can be reproduced.

- • The database must provide a wide range of capabilities with respect to the information that can be obtained from file systems under investigation.

NSRL

The primary focus of the NSRL is to aid computer forensics examiners in their investigations of computer systems.

The majority of stakeholders are in federal, state and local law enforcement in the United States and internationally.

These organizations typically use the NSRL data to aid in criminal investigations.

CFTT

The goal of the CFTT project at NIST is to establish a methodology for testing computer forensic software tools through the development of general tool specifications, test procedures, test criteria, test sets, and test hardware. The results provide the information necessary for toolmakers to improve tools, for users to make informed choices about acquiring and using computer forensics tools, and for interested parties to understand the tools capabilities.

The testing methodology developed by NIST is functionality driven. The activities of forensic investigations are separated into discrete functions, such as hard disk write protection, disk imaging, string searching, etc. A test methodology is then developed for each category. After a test methodology is developed it is posted to the web.

CFReDS

The Computer Forensic Reference Data Sets (CFReDS) provide to an investigator documented sets of simulated digital evidence for examination.

Since CFReDS has documented contents, such as target search strings seeded in known locations, investigators can compare the results of searches for the target strings with the known placement of the strings.

Investigators can use CFReDS in several ways including validating the software tools used in their investigations, equipment check out, training investigators, and proficiency testing of investigators as part of laboratory accreditation.

The CFReDS site is a repository of images. Some images are produced by NIST, often from the CFTT (tool testing) project, and some are contributed by other organizations.

CFReDS

In addition to test images, the CFReDS site contains resources to aid in creating test images.

These creation aids are in the form of interesting data files, useful software tools and procedures for specific tasks.

The CFReDS web site is http://www.cfreds.nist.gov.

International Standards The Scientific Working Group on Digital Evidence (SWGDE) was established

in February 1998 through a collaborative effort of the Federal Crime Laboratory Directors. SWGDE, as the U.S.-based component of standardization efforts conducted by the International Organization on Computer Evidence (IOCE), was charged with the development of cross-disciplinary guidelines and standards for the recovery, preservation, and examination of digital evidence, including audio, imaging, and electronic devices.

The following document was drafted by SWGDE and presented at the International Hi-Tech Crime and Forensics Conference (IHCFC) held in London, United Kingdom, October 4-7, 1999. It proposes the establishment of standards for the exchange of digital evidence between sovereign nations and is intended to elicit constructive discussion regarding digital evidence. This document has been adopted as the draft standard for U.S. law enforcement agencies.

http://www.fbi.gov/hq/lab/fsc/backissu/april2000/swgde.htm

Macintosh Operating System (MAC OS X)

Early MAC OS used HFS (Hierarchical file system) OS X uses HFS+ (optional) and also supports Unix File System

OS 9 supports Volumes. Volume can be all or part of the storage media for hard disks

Newer MACs booted can be booted from CD, DVD, Firewire drive. Older systems booted from hard drive

Some forensics tools special for OS X. Some other Windows tools can also be used

Unix/Linux Operating System

Everything is a file including disk drives, monitors, tape drives, network interface cards, etc.

Unix has four components for its file system

- Boot block, superblock, Inode, data block

- Block is smallest disk allocation

- Boot clock has bootstrap code, superblock has system information, Inode is assignee to every file allocation unit., data blocks store directories and files

Forensic examiner must understand the boot process of the operating system

Disk partitions in Unix/Linus is very different from Windows. In Unix/Linux partitions are labeled as paths.

Papers for Lecture on September 24, 2009Tamper Detection and Forensics Analysis

Richard T. Snodgrass, Stanley Yao and Christian Collberg, "Tamper Detection in Audit Logs," In Proceedings of the International Conference on Very Large Databases, Toronto, Canada, August–September 2004, pp. 504–515.

- Tamper Detection in Audit Logs Did the problem occur? (e.g. similar to intrusion

detection) Kyri Pavlou and Richard T. Snodgrass, "Forensic Analysis of

Database Tampering," in Proceedings of the ACM SIGMOD International Conference on Management of Data (SIGMOD), pages 109-120, Chicago, June, 2006.

Who caused the problem (e.g., similar to digital forensics analysis)