Forensic APFS File Recovery

Abstract

In forensic computing, especially in the field of postmortem file system forensics, the reconstruction of lost or deleted files plays a major role. The techniques that can be applied to this end strongly depend on the specifics of the file system in question. Various file systems are already well-investigated, such as FAT16/32, NTFS for Microsoft Windows systems and Ext2/3/4 as the most common Linux file systems and HFS/HFS+ for macOS. There also exist tools, such as the famous Sleuthkit by Brian Carrier that provide file recovery features for those file systems by interpreting the file system's internal data structures. APFS is the new file system for Apple devices that is applied by default on all current iOS mobile devices, as well as macOS since High Sierra, and is thus currently rolled out on a large number of devices. However, for APFS, no forensic file recovery methodologies have been developed so far. In this paper, we propose different approaches to identify and recover (deleted) files on an APFS file system. We implemented our approaches as a proof of concept tool and evaluate those against each other and against file carving.