File Carving with the Foremost tool

File carving is an important subject area in computer forensics. It can be used by a forensics expert to recover hidden files and verify that those files were present on a suspected computer.

The purpose of this article is to explain what file carving is, what it is used for and how it is processed.

We will focus on the Foremost tool, what can be done with this tool and how to get it.

Keywords: file carving ; foremost ; traces

File carving is a field of computer forensics in which we are searching for hidden or deleted files based on raw data from a disk or flash memory.

File systems all have metadata describing the hierarchy of stored documents (folders tree structure, files…) but file carving does not rely on these metadata but rather on raw data to identify and recover files.

A file can be identified by its header and footer for example a jpeg files raw data alays starts with 0xFFD8 and always ends with 0xFFD9.

We call these headers “magic numbers” or “file signatures”. A list of known file signatures can be found here: https://en.wikipedia.org/wiki/List_of_file_signatures .

Foremost is a software designed for data recovering and running on Linux machine in command line, there's no graphical user interface.

It was originally designed by Kris Kendall and Jesse Kornblum (special agents of the U.S. Air Force Office of Special Investigations ) in March 2001.

The tool read and copy parts of the drive into the memory of the computer running the programm. Foremost then process file carving to search in the memory for a file header. When a file header is found the tool writes it in an output file and also writes the data following this header until a footer is found or until the possible size limit of the file is achieved. All the output files are written in an output directory allowing users to consult them.

A nice fact about foremost is that it is desinged for ignoring the file system so he can process file carving whatever the file system used on the investigated disk.