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Apple Mac OS X tips and tweaks

Securely delete files in secure disk vaults

Keith wrote, "Got a question on your tutorial, Hide your files in secure disk vaults." If I want to delete either some of the data in a vault or the entire vault, is it necessary to use secure delete or since the data is encrypted, just delete the data?"

Questions about articles on this site are welcome, so thanks for writing Keith. It's an important issue and if you simply delete a file and it ends up in the Trash, couldn't someone then recover it? Is it still encrypted or not? If it is then there's nothing to worry about, but if it isn't then it's a security problem.

You have to understand how OS X works and Finder never deletes files, instead it simply moves them to the Trash folder. There doesn't appear to be a way to delete a file using Finder without moving it to the Trash. You can open a Terminal window and type in a complex command to delete a file without moving it to the Trash, but who wants to do that?

There isn't a single global Trash folder that collects all deleted files and each disk - internal, external, USB flash memory drives, mounted disk images, and so on - has its own Trash folder. The Trash folder on each disk is hidden so that you can't see it, but it's there. A deleted file stays on the disk it was deleted from and it is simply moved from whatever folder it is in to the hidden Trash folder on that same disk.

When you click the Trash icon in the dock and open the Trash folder, what you see is actuallly the contents of the Trash folder on the internal disk, plus the Trash folders on any mounted disks. It looks like one Trash folder, but the file listing is actually a list of all files in all Trash folders on all disks. If you unmount or eject a disk, its Trash folder will no longer be available and so the files it contains will no longer be visible if you open the Trash.

Try this...
1 Create a secure disk with Disk Utility
2 Put a file in there
3 delete it
4 Open the Trash and you'll see the deleted file
5 Eject the secure disk and you'll see the file disappear from the Trash folder

(It's hard to see if you have a zillion items in the Trash folder, so empty it first.)

Providing you eject a secure disk, no-one can access a file that's been deleted on it. This is because it is still on the secure disk and is still encrypted. If you mount the disk it re-appears in the Trash though and if you walk away from your Mac and leave the disk mounted, someone could come along and copy the file out of the trash. You must empty the Trash to really delete it.

RAW Trash securely deletes files without moving them to the Trash.


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