5.2 Evidence collection and preservation
11 min read•august 20, 2024
Evidence collection and preservation are critical components of network security and forensics. These processes ensure digital evidence remains intact and admissible in legal proceedings, protecting its integrity from tampering or loss.
Proper techniques for collecting and preserving evidence are essential for investigating cybercrime and security incidents. From to network traffic, understanding different types of digital evidence and following best practices helps maintain a strong and supports legal .
Importance of evidence preservation
- Evidence preservation is crucial in network security and forensics to ensure the integrity and admissibility of digital evidence in legal proceedings
- Proper preservation techniques prevent tampering, contamination, or loss of valuable data that could be critical in investigating cybercrime or security incidents
- Failing to preserve evidence correctly can lead to dismissal of cases or challenges to the credibility of the forensic analysis
Legal admissibility requirements
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- Digital evidence must be collected, preserved, and presented in a manner that meets legal standards for admissibility in court
- Admissibility requirements include relevance, authenticity, reliability, and compliance with legal procedures
- Failure to meet these requirements can result in evidence being deemed inadmissible, weakening the case
Chain of custody procedures
- Chain of custody refers to the documented trail of evidence handling from collection to presentation in court
- Proper chain of custody procedures involve:
- Recording each transfer of evidence
- Documenting the identity of individuals accessing the evidence
- Maintaining a secure and tamper-evident storage
- A well-maintained chain of custody helps establish the authenticity and integrity of the evidence, reducing challenges to its admissibility
Types of digital evidence
- Digital evidence in network security and forensics can take various forms, each requiring specific collection and preservation techniques
- Understanding the different types of digital evidence is essential for effective investigation and analysis
- Key types of digital evidence include volatile data, network traffic, system logs, and file system artifacts
Volatile vs non-volatile data
- Volatile data refers to information stored in a computer's memory (RAM) that is lost when the system is powered off
- is stored on persistent storage devices (, SSDs) and remains even without power
- Collecting volatile data requires live system acquisition techniques, while non-volatile data can be acquired from powered-off systems
Network traffic captures
- Network traffic captures (packet captures) record the data transmitted over a network
- Captured network traffic can reveal communication patterns, protocols used, and content of transmissions
- Network traffic evidence is useful in investigating network-based attacks, data exfiltration, and communication between malicious actors
System and application logs
- System logs record events and activities on a computer system, such as user logins, process execution, and system errors
- Application logs capture events specific to a particular software application, such as web server access logs or database transaction logs
- Log analysis can help reconstruct timelines, identify suspicious activities, and trace user actions
File system artifacts
- File system artifacts include files, directories, and metadata stored on a computer's storage devices
- Artifacts of interest may include documents, images, configuration files, and history records
- File system analysis can reveal the presence of malware, user-created content, and evidence of data tampering or deletion
Evidence collection best practices
- Following best practices during evidence collection is essential to maintain the integrity and admissibility of digital evidence
- Best practices ensure that the evidence is collected in a forensically sound manner, minimizing the risk of alteration or contamination
- Key best practices include minimizing data alteration, documenting the process, using forensic imaging techniques, and verifying integrity through
Minimizing data alteration
- Digital evidence is sensitive to changes, and any alteration can impact its admissibility and reliability
- Investigators should use write-blocking devices when accessing storage media to prevent inadvertent modifications
- Live system acquisition should be performed using forensically sound tools and techniques to minimize the impact on the running system
Documenting the process
- Thorough documentation of the evidence collection process is crucial for maintaining the chain of custody and demonstrating adherence to best practices
- Documentation should include:
- Date and time of collection
- Tools and techniques used
- Personnel involved
- Any deviations from standard procedures
- Detailed documentation helps establish the credibility of the evidence and the forensic process
Using forensic imaging techniques
- Forensic imaging involves creating an exact bit-for-bit copy of a storage device or memory
- Forensic images preserve the original evidence and allow analysis to be performed on the copy, leaving the original untouched
- Common forensic imaging formats include raw (dd), Expert Witness Format (EWF), and Advanced Forensic Format (AFF)
Hashing for integrity verification
- Hashing is a cryptographic process that generates a unique fixed-size value (hash) for a given input
- Calculating hash values of the original evidence and the collected copies allows for integrity verification
- Common hashing algorithms used in forensics include MD5, SHA-1, and SHA-256
- Matching hash values confirm that the collected evidence is an exact replica of the original
Live system data acquisition
- Live system data acquisition involves collecting evidence from a running computer system
- It is necessary when dealing with volatile data or when immediate response is required
- Key aspects of live system acquisition include memory capture, collecting running processes and network connections, and gathering volatile data
Memory capture tools
- Memory capture tools are used to create a forensic image of a computer's RAM
- Tools like , WinPmem, and LiME can capture the contents of memory, including running processes, network connections, and encryption keys
- Memory captures provide valuable insights into the system's state at the time of acquisition
Running processes and network connections
- Collecting information about running processes and network connections is crucial in live system acquisition
- Tools like pslist (Sysinternals) and netstat can enumerate running processes and active network connections
- Analyzing this data can reveal malicious processes, suspicious network activity, and communication with command and control servers
Collecting volatile data
- Volatile data, such as clipboard contents, temporary files, and cached information, can provide valuable evidence
- Tools like DumpIt and Magnet RAM Capture can collect volatile data from a running system
- Volatile data should be prioritized during live system acquisition as it is lost when the system is powered off
Dead system data acquisition
- Dead system data acquisition involves collecting evidence from a powered-off computer or storage device
- It is used when the system is no longer running or when a more thorough and forensically sound acquisition is required
- Key aspects of dead system acquisition include using write blockers, creating forensic disk images, and deciding between partial and full
Write blockers for drive preservation
- Write blockers are hardware or software tools that prevent any write operations to a connected storage device
- They ensure that the original evidence remains unaltered during the acquisition process
- Hardware write blockers are preferred for their reliability and compatibility with various storage interfaces (SATA, IDE, USB)
Forensic disk imaging formats
- Forensic disk imaging involves creating a bit-for-bit copy of a storage device
- Common forensic imaging formats include:
- Raw (dd): A simple format that creates an exact copy of the source device
- Expert Witness Format (EWF): A proprietary format used by that includes compression and metadata
- Advanced Forensic Format (AFF): An open-source format that supports compression, encryption, and metadata
- The choice of imaging format depends on the tools used and the specific requirements of the investigation
Partial vs full disk imaging
- Full disk imaging creates a copy of the entire storage device, including all partitions and unallocated space
- Partial disk imaging focuses on specific partitions or files of interest, reducing the time and storage requirements
- Full disk imaging is preferred when a complete and thorough analysis is required or when the scope of the investigation is uncertain
- Partial disk imaging can be used when the relevant evidence is known to reside in specific locations or when time and resources are limited
Network-based evidence collection
- Network-based evidence collection involves capturing and analyzing data transmitted over a network
- It is crucial in investigating network-based attacks, data exfiltration, and communication between malicious actors
- Key techniques in network-based evidence collection include packet capturing, NetFlow data analysis, and collecting data from network devices
Packet capturing techniques
- Packet capturing involves recording the data packets transmitted over a network
- Tools like Wireshark, tcpdump, and Tshark can capture network traffic in real-time or save it for later analysis
- Packet captures can reveal the content of network communications, including emails, web traffic, and file transfers
NetFlow data analysis
- NetFlow is a network protocol developed by Cisco that collects IP traffic information
- NetFlow data includes source and destination IP addresses, port numbers, protocols, and traffic volume
- Analyzing NetFlow data can help identify patterns of network activity, detect anomalies, and investigate security incidents
- Tools like SiLK (System for Internet-Level Knowledge) and nfdump can analyze NetFlow data for forensic purposes
Collecting data from network devices
- Network devices, such as routers, switches, and firewalls, can store valuable evidence
- Device logs can provide information about network events, configuration changes, and security alerts
- Network device configurations can reveal security weaknesses, misconfigurations, and unauthorized changes
- Collecting data from network devices may require specialized tools and knowledge of the specific vendor and model
Cloud and virtualized environments
- Cloud computing and virtualization technologies present unique challenges for digital forensics
- Evidence in cloud and virtualized environments is often distributed, ephemeral, and under the control of third-party providers
- Key considerations in cloud and virtualized forensics include the challenges, acquiring data from providers, and collecting evidence from virtual machines
Challenges in cloud forensics
- Jurisdiction and data location issues, as evidence may be stored in multiple geographic locations
- Limited control over the physical infrastructure and the need to rely on cloud service providers for access
- The dynamic nature of cloud environments, with data being created, modified, and deleted rapidly
- The use of virtualization technologies, which can complicate and analysis
Acquiring data from cloud providers
- Obtaining evidence from cloud service providers often requires legal processes, such as subpoenas or court orders
- Providers may have different policies and procedures for responding to evidence requests
- Investigators need to be familiar with the specific tools and APIs provided by each cloud platform (AWS, Azure, Google Cloud) for data acquisition
- Chain of custody documentation is crucial when acquiring evidence from third-party providers
Collecting evidence from virtual machines
- Virtual machines (VMs) are software-based emulations of physical computers
- Collecting evidence from VMs involves capturing the virtual hard disk (VHD) files and any associated snapshots
- Specialized tools, such as VMware's vSphere Client or Hyper-V Manager, can be used to access and acquire VM data
- Live system acquisition techniques may be necessary to capture volatile data from running VMs
Mobile device forensics
- Mobile devices, such as smartphones and tablets, contain a wealth of digital evidence
- Mobile device forensics involves collecting and analyzing data from these devices in a forensically sound manner
- Key aspects of mobile device forensics include iOS and Android acquisition methods, logical and physical extractions, and accessing cloud-synced data
iOS vs Android acquisition methods
- iOS and Android devices have different security models and acquisition methods
- iOS devices use a closed-source operating system and require specific tools (Cellebrite, GrayKey) for physical acquisition
- Android devices have a more open architecture and can be acquired using a variety of tools (XRY, UFED, Magnet AXIOM)
- The choice of acquisition method depends on the device model, OS version, and level of access required
Logical vs physical extractions
- Logical extraction involves collecting data from a device's logical storage, such as contacts, messages, and photos
- Physical extraction involves creating a bit-for-bit copy of the device's entire storage, including deleted and hidden data
- Logical extractions are generally faster and easier to perform but may not capture all relevant evidence
- Physical extractions provide a more comprehensive view of the device's data but require specialized tools and may be more time-consuming
Accessing cloud-synced data
- Mobile devices often sync data with cloud services (iCloud, Google Drive) or back up data to the cloud
- Accessing cloud-synced data may require legal processes or consent from the device owner
- Tools like Elcomsoft Phone Breaker and Magnet AXIOM can acquire data from cloud backups and synced accounts
- Analyzing cloud-synced data can provide additional insights and evidence not available on the physical device
Evidence transportation and storage
- Proper transportation and storage of digital evidence are essential to maintain its integrity and chain of custody
- Evidence must be protected from physical damage, tampering, and unauthorized access during transportation and storage
- Key considerations include secure packaging for physical transport, using encrypted storage devices, and maintaining chain of custody documentation
Secure packaging for physical transport
- Physical evidence, such as hard drives or mobile devices, should be packaged in a manner that prevents damage and tampering
- Anti-static bags, padded envelopes, and shock-resistant containers can be used to protect evidence during transport
- Evidence should be sealed with tamper-evident tape and labeled with case information and handling instructions
Encrypted storage devices
- Digital evidence should be stored on encrypted storage devices to prevent unauthorized access
- Hardware-encrypted storage devices (self-encrypting drives) provide a high level of security and performance
- Software-based encryption (BitLocker, VeraCrypt) can also be used to protect evidence on standard storage devices
- Encryption keys and passwords should be securely managed and accessible only to authorized personnel
Chain of custody documentation
- Chain of custody documentation must be maintained throughout the transportation and storage process
- Documentation should include:
- Date and time of each transfer
- Identity of individuals involved in the transfer
- Unique identifiers for the evidence (serial numbers, hash values)
- Description of the packaging and storage conditions
- Proper chain of custody documentation helps ensure the admissibility and credibility of the evidence in legal proceedings
Legal considerations
- Digital forensics investigations often involve legal considerations and requirements
- Investigators must be aware of the legal framework governing the collection, analysis, and presentation of digital evidence
- Key legal considerations include obtaining search and court orders, ensuring the admissibility of evidence, and preparing for expert witness testimony
Search warrants and court orders
- In many jurisdictions, collecting digital evidence requires a valid search warrant or court order
- Investigators must demonstrate probable cause and specify the scope of the search in the warrant application
- Warrants should be executed in a timely manner and within the boundaries set by the court
- Failure to obtain or properly execute a warrant can result in evidence being deemed inadmissible
Admissibility of digital evidence
- Digital evidence must meet legal standards for admissibility in court
- Admissibility criteria include relevance, authenticity, reliability, and compliance with legal procedures
- Investigators should follow best practices in evidence collection, preservation, and analysis to ensure admissibility
- Challenges to the admissibility of digital evidence can be based on issues such as improper collection methods, breaks in the chain of custody, or questions about the reliability of forensic tools
Expert witness testimony preparation
- Digital forensics professionals may be called upon to provide expert witness testimony in legal proceedings
- Expert witnesses must have the necessary qualifications, training, and experience to testify about their findings
- Preparing for expert witness testimony involves:
- Reviewing case materials and evidence
- Preparing clear and concise explanations of technical concepts
- Anticipating and preparing for cross-examination questions
- Communicating findings in a manner that is understandable to non-technical audiences
- Effective expert witness testimony can be crucial in explaining the significance of digital evidence and supporting the case's legal arguments
Key Terms to Review (18)
Admissibility: Admissibility refers to the legal standard that determines whether evidence can be considered by a court during a trial. This concept is crucial in ensuring that evidence presented is both relevant and reliable, adhering to established rules and protocols. The proper handling, collection, and presentation of evidence are essential for establishing its admissibility, impacting the overall integrity of forensic investigations and the judicial process.
Chain of Custody: Chain of custody refers to the process of maintaining and documenting the handling of evidence from the moment it is collected until it is presented in court. This process ensures that evidence remains intact, unaltered, and is admissible in legal proceedings, as well as establishes a clear timeline of how evidence was handled and by whom.
Disk imaging: Disk imaging refers to the process of creating an exact, bit-for-bit copy of a storage device, such as a hard drive or SSD. This technique is essential for preserving digital evidence in forensic investigations, ensuring that the original data remains intact and unaltered while enabling detailed analysis of the copied data.
Duplicate copies: Duplicate copies refer to exact replicas of original data or evidence, created to ensure that the original remains unaltered and preserved during the investigative process. These copies are crucial for maintaining the integrity of the original data while allowing for analysis and examination without risking damage to the source material. Creating duplicate copies is an essential step in evidence collection and preservation to uphold legal standards and facilitate accurate forensic analysis.
Dynamic analysis: Dynamic analysis refers to the process of evaluating a system or software by executing it and observing its behavior during runtime. This method allows for the identification of vulnerabilities, bugs, and performance issues that might not be evident in static analysis. By monitoring how an application interacts with its environment while it runs, dynamic analysis provides critical insights into the real-time operations of the software.
EnCase: EnCase is a digital forensic tool widely used for evidence collection, preservation, and analysis in cyber investigations. It allows forensic experts to create a bit-by-bit image of digital storage devices while ensuring that the original data remains untouched and secure. This process is critical for maintaining the integrity of the evidence, facilitating thorough forensic imaging, file system analysis, and accurate reporting in cybercrime investigations.
Evidence Acquisition: Evidence acquisition refers to the process of collecting and securing digital evidence from various sources in a way that maintains its integrity and prevents tampering. This practice is crucial for ensuring that the evidence can be reliably used in legal proceedings or investigations. It involves careful planning, specific tools, and techniques that adhere to established protocols to preserve the original state of data.
FTK Imager: FTK Imager is a forensic imaging tool used to create bit-for-bit copies of digital evidence, ensuring that the original data remains untouched and preserved for analysis. This tool not only facilitates the creation of disk images but also allows users to preview files and folders without modifying the original evidence. Its functionalities are crucial for gathering, preserving, and analyzing digital evidence in various investigative contexts.
Hard Drives: Hard drives are data storage devices that use magnetic storage to read and write digital information. They are essential components in computers and other devices, providing the primary means of storing operating systems, applications, and user data. Understanding hard drives is crucial for effective evidence collection and preservation, as well as for creating forensic images that accurately represent the stored data.
Hashing: Hashing is a process that transforms input data of any size into a fixed-size string of characters, typically a hash code. This process is crucial for ensuring data integrity and authenticity, as it generates unique values for different inputs, making it easy to detect changes or tampering in the data. Hashing plays a significant role in digital forensics and evidence collection by creating fingerprints of files that can be used to verify their authenticity during investigations.
ISO/IEC 27037: ISO/IEC 27037 is an international standard that provides guidelines for the identification, collection, acquisition, and preservation of digital evidence in a manner that ensures its integrity and reliability. This standard emphasizes the importance of proper procedures and methodologies to secure digital evidence from various sources, ensuring it remains admissible in legal contexts. Adhering to these guidelines facilitates both evidence collection and the subsequent forensic reporting process, allowing for transparent and reproducible outcomes in investigations.
NIST Special Publication 800-86: NIST Special Publication 800-86 is a document that provides guidelines for integrating forensic techniques into the process of incident response. It emphasizes the importance of evidence collection and preservation to maintain the integrity of data while ensuring that forensic analysis is conducted systematically. This publication outlines best practices for collecting digital evidence, documenting findings, and reporting results to support both legal and organizational requirements.
Non-volatile data: Non-volatile data refers to information that is retained even when the power is turned off. This type of data is crucial in digital forensics as it allows investigators to retrieve important evidence from devices after they have been powered down. Understanding non-volatile data is essential for effective evidence collection and preservation, as it often contains critical information that can aid in legal investigations or security assessments.
Solid-state drives: Solid-state drives (SSDs) are data storage devices that use flash memory to store data, as opposed to traditional hard disk drives (HDDs) which rely on spinning disks. The lack of moving parts in SSDs allows for faster data access, increased durability, and lower power consumption, making them a popular choice for both consumer and enterprise applications, especially when it comes to evidence collection and preservation.
Static analysis: Static analysis is the examination of code or software without executing it, focusing on detecting potential vulnerabilities, bugs, or compliance issues within the source code or binaries. This method allows security professionals and developers to identify flaws early in the development process, ensuring that software is robust against various types of attacks. By leveraging disassembly and debugging techniques, static analysis can aid in forensic investigations and the collection of evidence while also assessing the effectiveness of obfuscation techniques and understanding anti-reverse engineering measures.
Volatile data: Volatile data refers to information that is temporarily stored in a computer's memory, such as RAM, and is lost when the device is powered off or rebooted. This type of data is crucial during evidence collection and preservation because it can provide immediate insight into the state of a system at a specific point in time. Forensic investigators prioritize volatile data to capture evidence that might disappear if not collected swiftly after an incident.
Warrants: Warrants are legal documents issued by a judge or magistrate that authorize law enforcement to conduct a search, seize evidence, or make an arrest. They are critical in ensuring that evidence collection is performed legally and that the rights of individuals are protected. Warrants must be based on probable cause and specify the place to be searched and the items to be seized, which directly ties into how evidence is collected and preserved as well as the procedures involved in forensic imaging.
Write-blocker: A write-blocker is a device or software tool that prevents any modification to a digital storage device during the process of data acquisition. By ensuring that data remains unchanged, it plays a crucial role in maintaining the integrity and authenticity of digital evidence. This is essential for preserving evidence from digital devices, creating forensic images, and conducting thorough file system analyses without altering the original data.