How to Use the Command 'dcfldd' (with Examples)

The command dcfldd is a potent tool primarily designed for forensics and security purposes. It builds upon the functionality of dd, a Unix command-line utility used for converting and copying files. However, dcfldd introduces additional features beneficial in digital forensic investigations, such as advanced hashing capabilities, which are crucial for ensuring data integrity during evidence collection and analysis. Originating from the U.S. Department of Defense’s Computer Forensics Lab, this tool provides a reliable method to clone disks or create images with cryptographic hashes, thereby verifying the authenticity of the copied data.

Use Case 1: Copy a Disk to a Raw Image File and Hash the Image Using SHA256

Code:

dcfldd if=/dev/disk_device of=file.img hash=sha256 hashlog=file.hash

Motivation:

This use case exemplifies a scenario where you need to create an exact copy of a disk and ensure its integrity using a cryptographic hash. Disk imaging is crucial in digital forensics as it allows for the preservation of a subject’s storage media for analysis, while the hashing process guarantees that the image has not been altered. A SHA256 hash is chosen for its cryptographic strength, providing a robust mechanism to detect even the slightest data changes. This process is fundamental when collecting digital evidence to ensure it remains intact during analysis and presentation in legal proceedings.

Explanation:

• if=/dev/disk_device: This argument specifies the input file, which in this context is the disk device you want to image. It could be something like /dev/sda on a Linux system, representing the entire disk.

• of=file.img: This argument determines the output file. Here, it specifies the name of the file where the disk image will be stored, such as file.img.

• hash=sha256: This argument sets the hashing algorithm to SHA256, which is applied to the data as it is being read. SHA256 is part of the SHA-2 family, known for its strong security features, ensuring the hash produced is unique to the data processed.

• hashlog=file.hash: This argument specifies the log file for recording the hash. The hash of the entire image is saved in file.hash, creating an audit trail. This log is crucial for verification purposes, providing proof that the data has remained unchanged post-imaging.

Example Output:

After executing the command, you might not see detailed output directly in the terminal, but the hash log file (file.hash) will contain an entry similar to the following:

SHA256 (file.img) = e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855

Use Case 2: Copy a Disk to a Raw Image File, Hashing Each 1 GB Chunk

Code:

dcfldd if=/dev/disk_device of=file.img hash=sha512|sha384|sha256|sha1|md5 hashlog=file.hash hashwindow=1G

Motivation:

This scenario is beneficial when you need continuous verification of the disk imaging process by generating a cryptographic hash for each 1 GB chunk of data. This can be useful in forensic investigations where large drives are involved. By hashing in chunks, you reduce the risks associated with imaging failures and can identify precisely where in the imaging process issues might occur. Furthermore, providing options to use various hashing algorithms allows compatibility with different security standards and requirements.

Explanation:

• if=/dev/disk_device: Similar to the previous use case, this specifies the input file representing the device or partition to be copied.

• of=file.img: This denotes the file where the disk image should be saved.

• hash=sha512|sha384|sha256|sha1|md5: This argument specifies multiple hashing algorithms separated by a pipe character. This allows the tool to compute hashes using each of these algorithms, providing multiple forms of verification and ensuring compatibility with diverse requirements.

• hashlog=file.hash: This argument indicates that the hashes should be recorded in the file.hash log file, ensuring you have detailed, per-chunk verification records.

• hashwindow=1G: This instructs dcfldd to apply the hashing algorithms to each 1 GB segment of data, as opposed to the entire image. This chunk-based hashing can help in more granular verification and integrity checks.

Example Output:

Upon completion, the file.hash log file will contain entries for each 1 GB chunk, resembling the following format:

Chunk 1:
SHA512: 1f40fc92da... (truncated for brevity)
SHA384: 30ae4f179... (truncated for brevity)
...
Chunk 2:
SHA512: a4a1f27f0c... (truncated for brevity)
SHA384: 7e8b7e984... (truncated for brevity)
...

Conclusion:

The dcfldd command proves invaluable in scenarios involving digital forensic investigations and security processes, where it is essential to create verifiable digital copies of storage media. Through its capability to generate cryptographic hashes while imaging, it guarantees data integrity, providing credible evidence that can withstand scrutiny in legal proceedings. Both use cases highlighted the versatility of dcfldd in handling disk imaging and hashing, catering to forensic examiners’ needs for precision and robustness in data handling.