CHFI (312-49) Digital Forensics Simulation

Investigation Scenario

During a corporate espionage investigation at a financial firm in Chicago, Illinois, the incident response team escalated the case to digital forensics. A key suspect is believed to have securely deleted scanned documents and photographs linking them to an external competitor. The suspect's primary workstation drive was imaged using an industry-standard write-blocker, resulting in an E01 forensic image file. MFT entries for the suspected files have been overwritten.

The forensic examination team is currently executing raw file carving operations across unallocated disk space to recover the deleted evidentiary artifacts.

Evidence Collected

The forensic tool extracted multiple contiguous data fragments from unallocated clusters. Initial hex dumps of the leading clusters reveal the following file signatures:

Question

During a forensic investigation in Chicago, Illinois, analysts attempt to recover image fragments from unallocated disk space. One fragment begins with the hexadecimal sequence FF D8 FF E0 and ends with FF D9, while another begins with 42 4D followed by header data specifying dimensions and color depth. Based on these file signatures, which image file format does the first fragment represent?

Expert Analysis

• 1. What evidence shows: The raw hex dump of Artifact 1 explicitly reveals the header bytes `FF D8 FF E0` followed shortly by the ASCII string `JFIF`. The sector block successfully concludes with the trailer bytes `FF D9`. Artifact 2 shows the header `42 4D`.
• 2. Forensic Stage: This falls under the Examination and Analysis phase, specifically executing data carving and file signature analysis on unallocated space to bypass the compromised Master File Table (MFT).
• 3. Why correct answer is correct (B - JPEG): The hexadecimal sequence `FF D8 FF E0` (or `FF D8 FF E1` for EXIF) is the universal magic number (file header) denoting a Joint Photographic Experts Group (JPEG) image file. The sequence `FF D9` marks the End of Image (EOI) trailer, confirming a complete file boundary.
• 4. Why others are wrong:
  - A (PNG): Portable Network Graphics begin with the signature `89 50 4E 47 0D 0A 1A 0A`.
  - C (BMP): Bitmap images begin with `42 4D` (ASCII for "BM"). This matches the second fragment in the scenario, but the question explicitly asks about the first fragment.
  - D (GIF): Graphics Interchange Format files begin with `47 49 46 38 37 61` (GIF87a) or `47 49 46 38 39 61` (GIF89a).
• 5. Real-world forensic action: The investigator would configure their forensic carving tool (e.g., Foremost, Scalpel, or FTK/EnCase carving features) to search for these specific byte sequences. By defining the header (`FF D8`) and footer (`FF D9`), the tool can extract the raw binary data between those offsets and reconstruct the deleted photograph for evidentiary review.