Hi,
When I overwritten a data with only 1 pass or when the data is superscript, a lost the old data forever or not? Why I need more than 1 pass to secure delete my data?
Last edited by seventrad; 12 Jul 2011 at 06:29. Reason: Solved
If data is overwritten once, it is gone. I'm not sure what you mean when it is superscript, though.
I was not clear, sorry!
If when I use a "erase software" with only 1 pass or when data is overwritten by another file of SO (data file, mp3, movie...), why exists many software with many methods of data erase (CCleaner, Eraser, Active@ Kill Disk, PGP...) ?
Methods of Data Erase:
- Bruce Schneier's algorithm
- Canadian OPS-II
- DoD 5220.22 M
- Gutmann's algorithm
- German VSITR
- HMG IS5 Baseline
- HMG IS5 Enhanced
- Navso P-5329-26 (RL)
- Navso P-5329-26 (MFM)
- NCSC-TG-025
- Russian GOST p50739-95
- US Army AR380-19
- US Air Force 5020
The multiple passes date back to hard drives of many generations ago where data storage was much less dense and provided for greater ability for recovery with very sophisticated software. Current hard drive density doesn't nearly as easily allow for such things any more, so the multiple passes are for added feeling of security rather than actual. Data overwritten once on any remotely recent hard drive is gone. At best, with very expensive microscopy equipment, parts of sparse data could be recovered, but even then you'll be lucky to find anything contiguous or that you'd be able to piece back together into something whole.
There are differences about this subject: https://www-secure.symantec.com/conn...ng-really-safe
As far as I'm aware, no one has produced any results publicly of data recovery of anything substantial after overwriting data once on a modern hard drive.
If you are just concerned about making sure your data is not recoverable, you can overwrite the data 35 times if that will make you feel more comfortable that it's gone.
Data erasure at WikipediaAccording to the 2006 NIST Special Publication 800-88 Section 2.3 (p. 6): "Basically the change in track density and the related changes in the storage medium have created a situation where the acts of clearing and purging the media have converged. That is, for ATA disk drives manufactured after 2001 (over 15GB) clearing by overwriting the media once is adequate to protect the media from both keyboard and laboratory attack."
As a practice however, I use CCleaner's 7 pass option when running it.
As FliGi7 points out, this is due to very high density media. In older drive a, say 500MB drive would have 3 platters and therefore low density of data. I am currently running a 500GB drive which has only one platter.
try Eraser:
Eraser
This allows many different options from single file erasing, erasing entire recycle bin and even erasing full HDD's or just the unused data on an active HDD
all on a wide array of erase types:
35 pass Gutmann
7 pass Schneier
7 Pass DoD
3Pass DoD E
1 pass first last 2k
1 pass PsuedoRandom Data
Edit: Sorry misread your question as well. Posted as an easy third party app that I like for it.
Geez guys!
Secure Erase / Wipe : Definition and Methods <--Method Three
for an 11 pass file shredder
Additional Secure Erase / Wipe Information
SSD / HDD : Optimize for Windows Reinstallation
found something fun for everyone.
It is old and would, as stated above, only be useful to older drives under 15Gb, but I thought the information on how data is erased / recovered was an interesting insight into computer functionality.
This is a link (through Google) to a PDF:
counter forensic privacy tools - Google Search
and if you read just #passes on a file is not enough since the computer copies certain things in temp files and keeps track of file locations of these temps even after deletion of the original. when the temps are no longer being seen as deletable, they are still referenced and available on the unallocated disk space. meaning at least 1 pass of all unallocated disk space is a good idea as well.
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