File carving is a computer forensics technique to extract formatted files or data from a storage device without the original filesystem. It involves scanning the data and reconstructing files from file signatures, but can be complicated by fragmented files. It can recover data even after deletion or disk failure.
File carving is a technique used in computer forensics to extract a formatted file or data from a disk drive or other storage device without assistance from the filesystem that originally created the file. There are several methods and algorithms that can be used, but the process basically consists of scanning the data available on a storage device and then, one way or another, whether that information is a file or contains some important default information . A filesystem is not present during the file carving process, so all information on a disk must be evaluated for its context, which means that the process can take a long time and, depending on the state of the storage device, can have a low success rate. It’s incredibly difficult, but possible, to clip files from drives that have a high amount of file fragmentation. The end result of successful file carving is the reconstruction of a file such that its contents are fully present, although an acceptable result in some situations may be a partially reconstructed file if enough pertinent information is retrieved.
In some cases, due to hardware failure, human error, or malicious attack, the file system of a storage device and all information on it can be erased. Depending on how the information was removed, the disk itself may still contain all of the information that was previously there, but in an unordered and disorganized stream of bytes. One mechanism that makes file carving possible is that, when many filesystems delete a file from a drive, they do not remove the data but instead mark that area of the disk as available for new files. The old data remains until it is overwritten, and even then, there is still a chance that it can be recovered.
A basic technique used in file carving involves executing chunks of information on a disk looking for file signatures. This is structured data that points to the beginning of a file of a particular type. An example is the beginning of an image file which might contain the width and height of the image and some color palette data. If a block of data is found that exactly matches a file type header, an attempt is made to interpret the data following the header to see if it is indeed file data. If successful, this could lead to the reconstruction of the original file.
One complication that occurs in file carving has to do with fragmented files, which means that the file is stored in two or more different physical locations on a disk. Some techniques do not attempt to reconstruct these file types. Other methods use existing knowledge of filesystems to attempt to approximate where the other parts of a file might be located, although this process is very difficult.
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