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Wiping "underneath" the files.
wiping "underneath" the files
Hi, i got this idea dunno if it works I heard that the more times the disk is wiped the more difficult it is to recover the data by some advanced means, because each time the empty disk space is wiped a new "layer" of protection is added on top of deleted sensitive data. So the free space on disk gets many wipes/"layers" of protection but as the disk fills up over time the area allready occupied by files no longer get these "layers" written on it. If you have new empty disk and you put highly sensitive file at the beginning of it and then delete it and then install some new software and the deleted file gets overwritten by some other file then there is only one layer of data on top of that highly sensitive deleted data it may be easier to recover by attacker because area occupied by files cannot be wiped by eraser software anymore. What if eraser software could move files/clusters to somewhere else, wipe the place previously occupied by them with random data and then move the files/clusters back on to their original places going through all files/clusters of the disk (allmost like defragment utility). That way it could wipe "underneath" the files and the beginning of the drive would get same amount of wipe "layers" as the free space at the end of it, would this work?. |
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Previously defr wrote:
wiping "underneath" the files Hi, i got this idea dunno if it works I heard that the more times the disk is wiped the more difficult it is to recover the data by some advanced means, because each time the empty disk space is wiped a new "layer" of protection is added on top of deleted sensitive data. So the free space on disk gets many wipes/"layers" of protection but as the disk fills up over time the area allready occupied by files no longer get these "layers" written on it. Yes, true. Athough there is a limit on the "resolution" since older signals pretty fast drop below the basis-noise of the macgnetic coating. There is no way to recover them when that has happened. Presently sommercial data recovery companies claim they cannot even recover from a single overwrite. It is possible that this already weakens the signal to below the noise level. After all HDDs try to use the maximal possible data density. If you have new empty disk and you put highly sensitive file at the beginning of it and then delete it and then install some new software and the deleted file gets overwritten by some other file then there is only one layer of data on top of that highly sensitive deleted data it may be easier to recover by attacker because area occupied by files cannot be wiped by eraser software anymore. True. That is why your original secure deletion operation has to complete the job and you should never depend on any further operations adding to the security level. What if eraser software could move files/clusters to somewhere else, wipe the place previously occupied by them with random data and then move the files/clusters back on to their original places going through all files/clusters of the disk (allmost like defragment utility). That way it could wipe "underneath" the files and the beginning of the drive would get same amount of wipe "layers" as the free space at the end of it, would this work?. Yes. But instead try to overwrite the files securely the first time. If that is not possible (e.g. the file deletion is done insecurely by a piece of software you have no control over), just do a backup of the files not to be deleted, overwrite the entire source partition securely (on sector level, since directories and other admin structures could otherwise "cover" sectors, just wipeing under regular files is not enough), recreate the filesystem, copy your files back and securely delete the backups created in the intermediate step. This is about what you say, with some small but important details added. Regards, Arno -- For email address: lastname AT tik DOT ee DOT ethz DOT ch GnuPG: ID:1E25338F FP:0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F "The more corrupt the state, the more numerous the laws" - Tacitus |
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