Digital Forensics Profession and Investigations

Overview of Digital Forensics

  • Digital forensics is defined as the application of computer science (computer knowledge) and investigative procedures for a legal purpose. It involves the rigorous analysis of digital evidence following:

    • Proper search authority

    • Maintaining an unbroken chain of custody

    • Validation with mathematics

    • Use of validated tools

    • Repeatability of processes and results

    • Comprehensive reporting

    • Possible expert presentation in court

  • ISO Standard:

    • Ratified in October 2012: ISO 27037 Information technology — Security techniques.

  • Specialized Sub-Disciplines / Types of Digital Forensics:

    • Computer Forensics: Dead box forensics, Disk forensics.

    • Network Forensics: Cloud forensics, Wireless forensics.

    • Database Forensics

    • Malware Forensics

    • Email Forensics

    • Memory (Live) Forensics

    • Mobile Phone Forensics

    • Drone Forensics

    • Vehicle Forensics: Known for the principle that data collected by vehicle systems (which may present privacy concerns) offers critical evidence in forensic investigations.

Historical Context and Legal Foundations

  • Federal Rules of Evidence (FRE):

    • Created to ensure consistency in federal judicial proceedings.

    • Signed into law in 1973.

    • Most state rules map directly to or are derived from the FRE.

  • Key Law Enforcement Forensic Units:

    • 1984: The FBI formed the Computer Analysis and Response Team (CART) to handle cases involving digital evidence.

    • Late 1990s: CART teamed up with the Department of Defense Computer Forensics Laboratory (DCFL).

  • Statutory Laws vs. Case Law:

    • Technological change occurs at a rate faster than existing statutes can be enacted.

    • When specific statutes do not exist, case law is utilized. Case law allows legal counsel to apply precedents from previous similar cases to address legal ambiguity.

    • Forensic examiners must remain knowledgeable about recent court rulings regarding search and seizure in electronic environments.

Fourth Amendment and Search Warrant Exceptions

  • Fourth Amendment to the U.S. Constitution:

    • Protects individuals against unreasonable searches and seizures by government entities.

    • Separate search warrants might not always be necessary for digital evidence depending on jurisdiction and case context.

    • Every U.S. jurisdiction possesses case law governing the admissibility of evidence recovered from digital devices.

  • Warrant Exceptions for Law Enforcement:

    1. Consent Search: The target of the search explicitly gives permission to law enforcement to perform the search.

    2. Warrantless Search Under Exigent Circumstances: Occurs during urgent or emergency situations (e.g., risk of imminent physical harm, immediate destruction of digital evidence, or a suspect fleeing) where waiting to obtain a warrant is dangerous or impractical.

Special Legal Cases and Warrant Executions

  • FBI Playpen Case (2014–2016):

    • In 2014, the FBI seized Playpen, a darknet child pornography website, via a search warrant.

    • The FBI then obtained a warrant to deploy malware using its "Network Investigative Technique" (NIT) to infect the computers of site visitors.

    • Subpoenas were issued to Internet Service Providers (ISPs) ordering them to disclose names and addresses associated with identified IP addresses.

    • Search warrants were executed on individual locations to seize computers containing Child Sexual Abuse Material (CSAM).

    • In 2016, multiple cases were dismissed due to fundamental legal defects in the original NIT search warrant.

  • Execution and Challenges of Search Warrants:

    • A subject cannot read or validate a search warrant before it is actively executed by law enforcement.

    • Example Case: In June 2022, former Department of Justice (DOJ) attorney Jeffrey Clark was subjected to an unannounced FBI search of his home.

    • Spoofing Law Enforcement: Cybercriminals have actively spoofed law enforcement requests/subpoenas to fraudulently obtain private user information from service providers.

    • Geofence / Location Warrants: Used to identify thousands of potential suspects surrounding the January 6 attack on the U.S. Capitol; subject to ongoing appellate and Supreme Court scrutiny.

    • No-Knock Warrants: A highly controversial legal procedure subject to intense legal debate.

    • Customs and Border Protection (CBP) Border Searches: Border agents operate under distinct search and seizure standards at U.S. ports of entry and borders.

Electronic Storage Detection (ESD) Canines

  • Role of ESD K9s:

    • Electronics-sniffing canines are specially trained to detect hidden electronic storage devices including hard drives, USB flash drives, micro SD cards, and cell phones.

    • Primarily deployed in criminal investigations involving child sexual abuse where micro-scale digital evidence is deliberately hidden.

  • Chemical Markers Detected by ESD Canines:

    • Triphenylphosphine Oxide (TPPO): A chemical byproduct produced during the manufacturing process of electronic circuit boards and storage media. It is present in virtually all electronic devices containing circuit boards.

    • Hydroxycyclohexyl Phenyl Ketone (HPK): A chemical compound commonly found on optical and legacy storage media, including CDs, DVDs, and floppy disks.

Constitutional Rights and Private Sector Distinctions

  • First Amendment Protections:

    • Protections include Freedom of Religion, Freedom of the Press, Freedom of Assembly, Right to Petition the Government, and Freedom of Speech.

    • Freedom of Speech protects against government censorship or punishment; certain forms of speech (incitement to violence, defamation, fraud) are unprotected.

    • Private Corporations: Private companies are not bound by the First Amendment and do not recognize employee Freedom of Speech within corporate operations or policy enforcement. Employees can be legally terminated for social media postings or public statements.

Digital Forensics vs. Related Disciplines

  • Scope of Digital Device Investigation:

    • Collecting digital data securely.

    • Examining suspect data to establish details such as origin, metadata, and content.

    • Presenting digital evidence in legal proceedings.

    • Applying federal, state, and local laws to digital device handling.

  • Digital Forensics vs. Data Recovery:

    • Data Recovery: Focuses simply on retrieving lost or corrupted data that was deleted by mistake or lost due to power surges or system crashes.

    • Digital Forensics: Involves rigorous legal hold, chain of custody, deep artifact analysis, and scientific validation for presentation in administrative, civil, or criminal courts.

  • Investigations Triad: Forensics investigators work in coordinated teams alongside technical support and legal/investigative management.

Public-Sector vs. Private-Sector Investigations

  • Public-Sector Investigations:

    • Involve government law enforcement agencies responsible for criminal investigations and prosecution.

    • Strictly bound by the Fourth Amendment and procedural statutory constraints.

    • Key Legislation: Computer Fraud and Abuse Act (CFAA) passed in 1986; state computer crime laws were generally developed later.

    • Law Enforcement Workflow:

    1. Allegation of a crime made by a victim or witness to police.

    2. Police interview complainant and write an incident report.

    3. Incident report processed; management decides to open an investigation or log it into a police blotter (a historical record/database of reported incidents and crimes).

    • Key Public Sector Roles:

    • Digital Evidence First Responder (DEFR): Arrives at an incident scene, assesses physical/digital security, and takes immediate precautions to acquire and preserve physical media.

    • Digital Evidence Specialist (DES): Possesses specialized skills to process, extract, and analyze digital data, determining if additional subject matter experts are needed.

    • Affidavit: A sworn written statement of facts supporting evidence of a crime, accompanied by exhibits. Required by law enforcement to obtain a search warrant from a judge.

  • Private-Sector Investigations:

    • Focus on corporate policy violations, civil disputes, asset protection, and litigation defense (e.g., wrongful termination, corporate espionage, embezzlement, sabotage, discrimination, e-mail harassment).

    • Policies act as the internal "laws" of an organization.

    • Corporate Goal: Minimize or eliminate legal liabilities and financial exposure.

    • Acceptable Use Policy (AUP): Defines explicit rules for using company-owned computing assets, hardware, and networks.

    • Line of Authority: Establishes who holds the legal right within the organization to authorize an investigation, take physical possession of evidence, and access stored data.

    • Authorized Requesters include: Corporate Security, Ethics Office, Equal Employment Opportunity (EEO) Office, Internal Auditing, General Counsel / Legal Department.

    • Warning Banners: Standard security notices displayed on employee screens informing users that systems are monitored to remove expectations of privacy.

    • Core Banner Terms: Official business use only; monitoring active at all times; use of system constitutes explicit consent to monitoring; unauthorized/illegal activity subject to discipline or criminal prosecution.

    • Bring Your Own Device (BYOD): Blurs personal and corporate property boundaries. Connecting a personal mobile phone or device to a corporate network typically subjects the device to internal corporate investigation policies.

Systematic Approach to Digital Investigations

  • Core Forensic Role:

    • Gather evidence to prove or disprove allegations of criminal acts or policy violations.

    • Process suspect hardware while preserving evidence integrity on secondary media.

    • Maintain an unbroken Chain of Custody (the documented route evidence takes from initial seizure until final case disposition).

  • 12-Step Problem-Solving Methodology:

    1. Make an initial assessment of the case.

    2. Determine a preliminary design or approach.

    3. Create a detailed investigative checklist.

    4. Identify and gather required hardware and software resources.

    5. Obtain and copy evidence media.

    6. Identify potential forensic and procedural risks.

    7. Mitigate or minimize identified risks.

    8. Test the preliminary design and procedures.

    9. Analyze and recover digital evidence.

    10. Deeply investigate recovered data.

    11. Complete a comprehensive case report.

    12. Critique the case to improve future operations.

Evidence Collection and Physical Security

  • Physical Packaging Guidelines:

    • Use approved evidence bags to secure and catalog physical media.

    • Utilize computer-safe, static-dissipative products (antistatic bags and antistatic pads).

    • Package items inside well-padded containers to protect against mechanical shock.

    • Apply tamper-evident evidence tape over all open ports, drive bays, power inputs, and USB interface slots.

    • Write investigator initials and date directly across the tape boundary to ensure tamper detection.

  • Environmental Controls:

    • Store media within specific temperature and humidity tolerance ranges.

    • Maintain controlled transit conditions until evidence can be transferred into a locked evidence safe, secure cabinet, or evidence locker.

Attorney-Client Privilege (ACP) Investigations

  • Legal Obligations:

    • Under Attorney-Client Privilege (ACP) rules, all forensic findings and communications must be kept strictly confidential.

    • Attorneys often request physical printouts of digital data; examiners must educate legal counsel on proper electronic review methods.

  • Step-by-Step ACP Forensic Protocol:

    1. Request an official legal memorandum from the attorney directing the examiner to conduct the investigation.

    2. Request a formal list of search terms and keywords of interest.

    3. Initiate target analysis.

    4. Make two independent bit-stream images of the drive using different acquisition tools for each image.

    5. Calculate and compare hash signatures across all original files and created bit-stream images.

    6. Methodically process every portion of the drive and extract data.

    7. Run keyword searches against allocated and unallocated disk space.

    8. For Windows systems: utilize specialized tools to parse and extract data from the Windows Registry.

    9. For proprietary binary files (e.g., CAD drawings): obtain and use the native software package.

    10. For unallocated space recovery: use specialized software that filters out or replaces nonprintable data.

    11. Consolidate extracted data into clean directory trees.

    12. Minimize written communications; ensure all documents submitted to counsel contain the header: Privileged Legal Communication—Confidential Work Product.

    13. Assist attorneys and paralegals in interpreting technical findings.

Interviewing and Interrogating in High-Tech Cases

  • Distinction Between Processes:

    • Interview: A non-confrontational procedure conducted to collect factual information from witnesses or targets regarding specific case details.

    • Interrogation: An active process aimed at obtaining an admission of guilt or confession from a suspect.

  • Role of the Digital Forensics Specialist:

    • Assist law enforcement officers conducting interviews by formulating technically accurate questions and explaining expected technical answers.

  • Key Investigator Traits:

    • Demonstrating absolute patience.

    • Repeating or rephrasing questions systematically to extract facts from reluctant subjects.

    • Maintaining persistent tenacity throughout sessions.

Hardware, Forensic Workstations, and Write-Blockers

  • Forensic Workstations:

    • High-performance computers configured with extra media drive bays, high-speed interfaces, and pre-installed forensic software suites.

  • Write-Blocking Devices:

    • Hardware or software tools designed to prevent write commands from reaching evidence drives while allowing full read access.

    • Data Flow Mechanics: Data flows strictly in one direction — from the Evidence Storage Device through the Write-Blocker to the Imaging/Forensic Workstation — guaranteeing the original media cannot be altered during connection or imaging.

  • Essential Laboratory Resources:

    • Original storage media

    • Evidence custody forms

    • Static-safe evidence storage containers

    • Bit-stream imaging tools

    • Dedicated forensic workstation

    • Securable evidence locker, safe, or locked cabinet

Bit-Stream Copies and Evidence Acquisition

  • Bit-Stream Copy vs. Standard File Backup:

    • Bit-Stream Copy: A bit-by-bit duplicate of the physical storage medium, capturing every sector, track, allocated space, unallocated space, and slack space.

    • Standard Backup: Only copies active, known files recognized by the file system. Fails to capture deleted files, unallocated file fragments, hidden system structures, or raw email stores.

  • Bit-Stream Image File:

    • A single contiguous file or set of split files containing the exact bit-stream replica of a disk or partition.

    • When restored to secondary media, the target drive must match the original disk's size, model, and geometry.

  • Primary Rule of Computer Forensics:

    • Preserve the original evidence. Perform all analytical procedures exclusively on working copies of the bit-stream image.

  • Acquisition Environment:

    • Windows-based acquisition tools require hardware write-blockers when acquiring data from FAT or NTFS file systems to prevent automated OS write operations.

Data Recovery and Analysis Techniques

  • Target Data Recovery Types:

    • Deleted files (data remains on physical sectors until overwritten by new system data).

    • File fragments located in unallocated space.

    • Complete allocated files.

  • Autopsy Forensic Tool Workflow:

    1. Case Creation: Launch Autopsy -> Select New Case -> Enter Case Name -> Define Working Base Directory.

    2. Adding Data Source: Select Data Source Type -> Browse to Bit-Stream Image File -> Apply Default Settings in Configure Ingest Modules window.

    3. Browsing Extracted Data: Expand Views -> File Types -> By Extension -> Documents -> Select targeted file -> Click Tag and Comment -> Define New Tag Name.

    4. Analysis & Keyword Searching: Execute specific string/keyword searches across allocated and unallocated space -> View hits in Search Results Window -> Parse file contents in Data Area -> Export selected artifacts to output folders -> Review nonprintable/binary data using the Content Viewer -> Generate final case reports.

  • Recuva Software: A utility used for recovering deleted files on Windows operating systems.

Case Completion, Reporting, and Journaling

  • Documentation Requirements:

    • Maintain a detailed, real-time written journal documenting every analytical step, tool command, and system response. Notes are legal records admissible in court.

    • Ensure answers are recorded for the Six Ws: Who, What, When, Where, Why, and How.

    • Translate complex computer and network processes into clear terms for legal bodies.

  • Final Forensic Report:

    • Detailed report outlining all actions taken and findings discovered.

    • Attach automated reports (e.g., Autopsy Report Generator outputs in plain text, HTML, or Excel formats).

    • Standard of Proof: Evidence must yield repeatable findings (another examiner running the same steps on the same image must produce identical results).

    • Report must draw clear, objective conclusions regarding whether an individual committed a policy violation or illegal act.