On Wed, 4 Sep 2013, Piers Rowan <piers.rowan@recruitonline.com.au> wrote:
On 09/03/2013 10:02 PM, Russell Coker wrote:
You are assuming that the wiping does what it claims to do. I would be more inclined to trust that when I've written 100G of data to a 100G disk then whatever was there before is really gone.
This is the bit I haven't understood. If you want to protect the contents of a drive which not write pictures of your cat to the drive until it is full. If you align the block/disk size with the file then presumably there won't be any gaps or if there is then those fragments wont be enough to build any significant information.
With a filesystem it will be difficult to discover where on the disk a particular file is, there are ways of doing this (generally only used by boot- loader installation programs) but it will be too inconvenient to be useful. If you write to the entire disk it will wipe it all, no particular alignment is needed. Hard drives store things in sectors of 512 bytes or 4K (for newer/larger disks) so you just need to write to every sector. With hard drives there is the possibility that marginal sectors were remapped which could then be recovered. There is also the possibility that analogue signals that remain from previous writes that are discarded as noise in the normal read process can be read. Both of those are out of reach of most attackers. For SSDs there are different issues, the controller does a fair bit of work to map sector writes to erase blocks. Really if you want data to be safe then encrypt it on the disk. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/