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David_Gerard comments on Timeless Identity - Less Wrong

23 Post author: Eliezer_Yudkowsky 03 June 2008 08:16AM

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Comment author: David_Gerard 25 January 2011 10:25:43PM *  4 points [-]

Do you know what it takes to securely erase a computer's hard drive? Writing it over with all zeroes isn't enough. Writing it over with all zeroes, then all ones, then a random pattern, isn't enough. Someone with the right tools can still examine the final state of a section of magnetic memory, and distinguish the state,

Minor note: this claim is obsolete and should not be used to make the point you're trying to make.

Peter Gutmann's original list of steps to erase a hard drive is obsolete. Gutmann himself is particularly annoyed that it appears to have taken on the status of a voodoo ritual. As that Wikipedia article notes, "There is yet no published evidence as to intelligence agencies' ability to recover files whose sectors have been overwritten, although published Government security procedures clearly consider an overwritten disk to still be sensitive. Companies specializing in recovery of damaged media (e.g., media damaged by fire, water or otherwise) cannot recover completely overwritten files. No private data recovery company currently claims that it can reconstruct completely overwritten data." Overwriting with random data is enough in practice in 2011, and was in 2008 for that matter.

Comment author: wedrifid 26 January 2011 12:45:10AM *  2 points [-]

Scientists have played with electron microscopes and established that in principle someone with the right tools could examine the final state of a section of magnetic memory and distinguish an earlier state. It's just that nobody has said tools in practice and the engineering tasks to create tools that worked reliably for the task is an absolute nightmare.

One could argue that the quoted claim is technically correct.

Comment author: David_Gerard 26 January 2011 01:52:18AM *  -1 points [-]

Citation needed, one talkiing about hard disks as of 2008 at the earliest, or an equivalent magnetic problem.

A supporting claim needing to be stretched as far as "well, it's not technically false!" still strikes me as not being a good example to try to persuade people with.

Comment author: wedrifid 26 January 2011 02:14:07AM *  2 points [-]

Citation needed, one talkiing about hard disks as of 2008 at the earliest, or an equivalent magnetic problem.

I am reluctant to comply with demands for citations on something that is not particularly controversial and, more importantly, does not contradict the references you yourself provided. Apart from reading your own references (Gutmann and wikipedia) you can look at the most substantial criticism of the idea that there are real world agencies who could recover your overwritten data, that by Daniel Feenberg.

Gutmann mentions that after a simple setup of the MFM device, that bits start flowing within minutes. This may be true, but the bits he refers to are not from from disk files, but pixels in the pictures of the disk surface. Charles Sobey has posted an informative paper "Recovering Unrecoverable Data" with some quantitative information on this point. He suggests that it would take more than a year to scan a single platter with recent MFM technology, and tens of terabytes of image data would have to be processed.

His general point is that while there has been some limited success with playing with powerful microscopes the current process is so ridiculously impractical and unreliable that there is no chance any existing intelligence agency would be able to pull it off.

A supporting claim needing to be stretched as far as "well, it's not technically false!" still strikes me as not being a good example to try to persuade people with.

Not a position I have argued against, nor would I be inclined to.

Comment author: David_Gerard 27 January 2011 11:00:57AM 1 point [-]

Fair enough!