Digital Forensic Acquisition — A Deep Dive

 A complete, unaltered copy of the data is needed for analysis, but the original evidence must be kept undamaged and intact.

Types of Acquisition

1. Static Acquisition

• Device is powered off before imaging.

• Captures data from non-volatile storage (hard drives, USB drives, SSDs).

• Advantages: No running system means less risk of data changes during acquisition.

• Disadvantages: Volatile data (RAM, running processes) lost when powered off.

2. Live Acquisition

• Device is powered on and operational during acquisition.

• Captures volatile data (RAM contents, running processes, network connections) alongside storage data.

• Advantages: Access to data only available when system is running (encryption keys, active sessions).

• Disadvantages: Risk of altering data, system instability, requires careful handling.

3. Logical Acquisition

• Only specific files, folders, or file system metadata are copied, not an entire disk image.

• Faster and requires less storage space.

• Risk: May miss hidden, deleted, or unallocated data.

• Commonly used for mobile devices or cloud storage.

4. Physical Acquisition

• Bit-for-bit copy of entire storage media including all files, slack space, unallocated space, and deleted files.

• Enables recovery of deleted or hidden data.

• More time and storage intensive.

Acquisition Workflow — Step-by-Step

Step 1: Preparation

• Verify legal authority and obtain proper search warrants or permissions.

• Prepare clean forensic workstation with trusted, verified tools.

• Ensure all tools are updated and tested.

Step 2: Document the Scene and Device

• Photograph the device, serial numbers, cables, power state.

• Note device make, model, connections, and environment.

• Record system date/time and network details.

Step 3: Preserve the Original Evidence

• Use write blockers when connecting storage devices to prevent any writes.

• If live acquisition is needed, minimize interaction and document every action.

Step 4: Acquire the Data

• For static acquisition: create a bitstream image of storage media using tools like FTK Imager, EnCase, dd, or Guymager.

• For live acquisition: capture memory dump and other volatile data first, then capture storage data.

• For logical acquisition: extract specific files or directories using device-specific tools.

Step 5: Verify Integrity

• Generate cryptographic hash values (MD5, SHA-1, SHA-256) of the original media and acquired images to verify exactness.

• Save hashes securely to detect any later modifications.

Step 6: Secure Storage and Transport

• Store acquired images and original evidence in secure, access-controlled environments.

• Maintain detailed chain of custody documentation.

Key Concepts in Acquisition

1. Forensic Image

A bit-for-bit copy of a storage medium capturing every byte, including deleted files and slack space.

2. Hashing

Applying a cryptographic hash function to generate a unique digital fingerprint of data for integrity verification.

3. Write Blockers

Devices or software preventing modification to original evidence during acquisition.

4. Chain of Custody

A documented history tracking the evidence from collection to presentation in court, proving it has not been tampered with.

Tools Commonly Used in Acquisition