While APFS hardware encryption works in largely the same manner, the encryption also depends on keys that are stored within the specific security chip on a given system. This decryption requires the knowledge of the password of any user on the system or one of the various recovery keys. We’ve now discussed all of the information needed to access data on software-encrypted APFS volumes. Typedef struct j_file_extent_val j_file_extent_val_t // 0x18 Conclusion Let’s revisit the value half of an Object Map entry. Encrypted FS-Tree NodesĪ volume’s Object Map is never encrypted, but its referenced virtual objects may be, as is the case with FS-Tree Node on encrypted volumes. As we’ve discussed, File System Tree Nodes store the File System Records that contain the file system’s metadata, and File Extents contain the bulk of the data stored in a file’s Data Streams. There are primarily two sets of data protected with the APFS Volume Encryption Key: File System Tree Nodes and File Extents. In these cases, the tweak can not be inferred based on the block’s on-disk location, so we must learn the original tweak value used for encryption. If the encrypted block is ever relocated on disk, the data is not guaranteed to be re-encrypted with a new tweak. Knowledge of the AES key alone is not always enough for successful decryption. Every 512 bytes of encrypted data uses a tweak based on the container offset of the block’s initial storage. It allows the same plaintext to be encrypted and stored in different locations on disk and have drastically different ciphertext while using the same AES key. TweaksĪll encryption in APFS is based on the XTS-AES-128 cipher, which uses a 256-bit key and a 64-bit “tweak” value. Now that we know how to parse the File System Tree, Analyze Keybags, and Unwrap Decryption Keys, it’s time to put it all together and learn how to decrypt file system metadata and file data on encrypted volumes in APFS.
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