During A Criminal Case Investigation, A Computer Was Taken

During a criminal case investigation, a computer was taken as part of the evidence

During a criminal case investigation, a computer was taken as part of the evidence. The computer was found with a flash drive connected to one of the USB ports. It is suspected that this flash drive contains image files relevant to the case. Preliminary investigation revealed that the owner of the computer had the chance to delete some of the image files. Other files were renamed so that they do not look like image files. It is also suspected that steganography was used with some of the files to conceal important information. The passphrase used for this purpose is hidden in the device's slack space. List the general steps and tools required to begin investigation. In addition, because it is a high-level profile case, processes must be carefully documented. Perform and document the following so that the findings are court-ready: Acquire a bit-stream copy from the flash drive. Recover deleted files. Analyze all files (including recovered) using WinHex and look for image files by analyzing the file headers. Try to identify image files concealing information (steganography). Look for the passphrase for steghide stored in the device's slack space (look for: "steghide passphrase"). Recover information with steghide. Ensure the report is two pages excluding title and references.

Paper For Above instruction

Introduction

The digital forensics investigation of devices involved in criminal activity requires a systematic approach to ensure the integrity and admissibility of evidence. In cases where a computer and associated media such as a USB flash drive are involved, several investigative steps must be meticulously executed, documented, and supported by appropriate tools. This paper delineates a comprehensive methodology for investigating a suspect’s USB flash drive containing potentially hidden, deleted, or disguised image files, possibly combined with steganography, with an emphasis on preserving evidence integrity for court proceedings.

Initial Acquisition and Documentation

The first phase involves acquiring a bit-stream (or bit-by-bit) copy of the suspect media to preserve the original evidence and facilitate analysis. Using write-blockers is crucial to prevent any modification of data during acquisition. Tools like FTK Imager or dd (Linux) are typically used for creating forensically sound copies. Documentation of the acquisition process, including hash values (MD5/SHA-1/SHA-256), is vital for establishing chain of custody and ensuring the admissibility of the evidence in court.

Recovering Deleted Files

The next step involves recovering deleted files that may have been intentionally or unintentionally deleted. File recovery tools such as Recuva, PhotoRec, or Encase can scan the drive or image for remnants of deleted files. Deleted files in FAT or NTFS file systems often leave residual data in slack or unallocated space, which can be recovered using these tools. It is necessary to document recovered files, their attributes, recovery methods, and hash values for court presentation.

Analyzing Files with WinHex

All files, including those recovered, should be analyzed with a hex editor such as WinHex. This step involves examining file headers to confirm file types and identify hidden or disguised data. Image files typically have identifiable headers (e.g., JPEG: FF D8 FF, PNG: 89 50 4E 47). By scrutinizing headers, investigators can detect files that have been renamed to obscure their true nature. Analysis includes verifying whether files contain intact image headers and evaluating any anomalies that may suggest steganography or data concealment.

Detecting Steganography

Steganography involves hiding information within legitimate image files, often by manipulating least significant bits or embedding data in unused segments. Identifying steganography requires analyzing the image files for irregularities, such as unusual metadata, inconsistent header information, or anomalies detected through specialized tools such as Stegdetect or Steghide. Since the suspicion is that hidden data is present, detailed examination may involve inspecting pixel data, auxiliary data, or message embedding signatures. This process enhances the chances of locating concealed data and the passphrase for extracting additional information.

Locating the Passphrase in Slack Space

Passphrases used for steganography, such as with Steghide, are sometimes stored in slack space—the unused space within a disk cluster or within device slack space. To locate the passphrase, investigators employ hex editors (like WinHex) to examine the slack areas of the drive image or individual files. Searching for the string "steghide passphrase" within slack space can reveal the concealed passphrase, which is essential for extracting embedded data using steghide. Documenting findings involves capturing the exact location, data, and context of the passphrase within slack space.

Using Steghide for Data Extraction

If a passphrase is identified, steganographic data embedded within image files can be extracted using steghide. This command-line tool allows extraction of hidden data given the correct passphrase. The process involves selecting the targeted image file, supplying the passphrase, and extracting the embedded data to a secure location. Proper documentation of the extraction process, including command-line inputs, file hashes, and data recovered, enhances the court readiness of the findings.

Conclusion

Investigation of digital evidence involving potential data concealment through deletion, renaming, and steganography demands a structured approach emphasizing careful evidence handling, thorough analysis, and meticulous documentation. Acquiring a forensically sound image, recovering deleted data, analyzing files for anomalies, and extracting hidden information are critical steps. Employing tools like FTK Imager, WinHex, and steghide ensures a comprehensive investigation that withstands court scrutiny. These procedures contribute to establishing a clear, reproducible chain of custody and ensuring that findings are admissible and credible in judicial proceedings.

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