How to use the command dcfldd (with examples)
dcfldd is an enhanced version of the dd command that is specifically designed for forensics and security purposes. It provides additional features and options for disk imaging, hashing, and logging. This article will illustrate two use cases of the dcfldd command along with their code, motivation, explanation, and example output.
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 is helpful when you want to create a bit-by-bit copy of a disk and at the same time, verify the integrity of the image file using a cryptographic hash function like SHA256. By including the hashlog argument, you can also generate a log file that contains the hash value for future reference.
Explanation:
if=/dev/disk_device: Specifies the input file, in this case, the disk device from which you want to create the image file.of=file.img: Specifies the output file, which will be the raw image file that contains the disk’s data.hash=sha256: Specifies the hash algorithm to be used. In this example, SHA256 is used.hashlog=file.hash: Specifies the log file where the hash value will be stored.
Example output:
dcfldd 1.3.4+dev19: Started at 2022-07-15 10:00:00
500000+0 records in
500000+0 records out
256000000 bytes (256 MB, 244 MiB) copied, 2.000 s, 128 MB/s
SHA256 hash for file.img: 9e82caa8f212a481e2291e07866b011c4b4b8a4a8fdf55b97c7644e35986e1cd
dcfldd: Data written
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:
In some cases, it might be more efficient and practical to hash a disk image in smaller chunks rather than the whole image at once. This use case allows you to divide the disk image into 1 GB chunks and hash each chunk separately. This can be useful for parallel processing or when dealing with large disk images.
Explanation:
hash=sha512|sha384|sha256|sha1|md5: Specifies multiple hash algorithms to be used. In this example, sha512, sha384, sha256, sha1, and md5 are used.hashlog=file.hash: Specifies the log file where the hash values for each chunk will be stored.hashwindow=1G: Specifies the chunk size for hashing. The disk image will be divided into 1 GB chunks, and each chunk will be hashed separately.
Example output:
dcfldd 1.3.4+dev19: Started at 2022-07-15 11:00:00
1000000+0 records in
1000000+0 records out
512000000 bytes (512 MB, 488 MiB) copied, 4.000 s, 128 MB/s
SHA512 hash for file.img[0G:1G]: d05d19c2dc0395d1b248f75ccf4eb12f93a49f2daa636a60b8aa77d28ef807dafff6b2e5ddeea69664f88d26939e45403c15f421f3b097c532f28cc8105dd5c9
SHA384 hash for file.img[0G:1G]: 8f93817da0be5e5be44034e5a1d222f0ebea7fc86dec6180f1a313df537314ebb7321f9c8a87a91f338b4f450c7d804c2f6386e482722253e64bdfc6b8d7ab7f
SHA256 hash for file.img[0G:1G]: 4422d3f573b8d82d31e4cb1fea2cd8a5a2def37ab4ea9897d7f9e925581d209b
SHA1 hash for file.img[0G:1G]: 89a40ef3d510fb10f6f361c705e8daaf88706b7d
MD5 hash for file.img[0G:1G]: c2927c4a5e6deed5a714ccd2da1f2ef4
dcfldd: Data written
Conclusion:
The dcfldd command is a powerful tool for disk imaging, hashing, and logging in the field of forensics and security. It provides advanced features that are beneficial when creating and verifying disk image files. By understanding the different use cases and options of the dcfldd command, you can effectively utilize it in your forensic and security operations.
