Secure delete files—an alternative?

If you have truly sensitive data that must never be found after it is erased, then melt down the SSD or the Hard Disk.

With both SSDs and Hard Disks, if a sector goes bad, the device will logically replace the sector with a spare and the replaced sector will contain its original values. Hence the need to totally destroy the device if the data must never be uncovered after deletion.

With respect to SSDs. Think of an SSD organized as a case of egg cartons, where each carton holds a dozen (12) eggs. When you write sector the data is put into an empty egg slot (eg. #22). When you re-write that sector, the data is put into a different egg slot (eg #153), logical sector mapping information is updated but the original data is still sitting in the previous egg slot (#22) which is not accessible via normal disk access tools, but is accessible to the right kind of tools that knows how to take to the SSD at the device interface level.

The SSD can ONLY pre-clear an entire egg carton, so until slots #13-24 are all no longer holding current data, #22 is going to hang around.

SSDs also contains lots of spares. When you decided to zero all free space, the SSD may just use its spares to provide the logical sectors and still leave #22 holding old data.

If the SSD has lots and lots of little holes, like #22, then it may decide to copy out #13-21 and #23-24 to somewhere else, then pre-clear the egg carton holding #22. At that point in time, #22 will be gone. Until the SSD decides that the egg carton holding #22 is going to be pre-cleared, #22 and its old data is going to remain.

So if you do not want anyone to find the old data in #22 you totally destroy the SSD.

Another approach that you are not going to like, as you feel encryption can be cracked, is to create an encrypted disk image, put the sensitive data into the encrypted disk image. Mount the encrypted disk image, enter the decryption password, then use that sensitive data. When you no longer want that sensitive data, throw away the password, and delete the disk image. The disk image will not have the same encryption key as FileVault, and when you destroy the password, it can only be cracked with expensive computing power.

But if you do not trust that, melt down your SSD. Open it up, take a blowtorch to it, and melt it into slag.

If you encrypt the SSD with File Vault and then reformat it, the passcode for File Vault will be removed by the reformat. Even if someone knows the passcode, the data can no longer be decrypted. While the data is still there, it is encrypted and hence useless.

I think you worry too much. You need to ask how much your data is worth? Act accordingly.

R