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Is my drive 'really' secure after wiping ?

 
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serene
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Joined: Sun Jun 19, 2005 1:43 pm
Posts: 111

PostPosted: Tue Jan 01, 2013 8:47 pm    Post subject: Is my drive 'really' secure after wiping ? Reply with quote

Hi.

I usually wipe my drives by;
dcfldd bs=1M if=/dev/zero of=/dev/sda

I tried the 'secure' ATA method, which in theory should wipe the protected areas and bad sectors.

Questiion;
Since dd or dcfldd writes low level zeros directly to the disk, shouldn't it overwrite any and all areas of the drive, including reserved areas ?

I'd rather use dd instead of the ATA method if it acomplishes the same thing.

Thank you.
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Dutch_Master
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Joined: Tue Mar 27, 2007 2:49 am
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PostPosted: Tue Jan 01, 2013 9:09 pm    Post subject: Reply with quote

You need to weigh up the risks against the effort: what info is on the disk and how likely is it the new owner of the disk (assuming you wipe it before flogging it off) is going to try to retrieve any residual info.

If you want it done properly, format the drive for a different filesystem (XFS, ext4, JFS, NTFS, ZFS, (V)FAT) then copy data to it from /dev/null and /dev/random (minimum 5x each), then reformat in a totally different FS and start the copy process again. Use all above file systems in that order. No "quick format", the full conversion!
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serene
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Joined: Sun Jun 19, 2005 1:43 pm
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PostPosted: Tue Jan 01, 2013 9:39 pm    Post subject: Reply with quote

Dutch_Master,

Thank you, however this does not address my question.

If hard drives are wiped via my example, will the reserved, protected, and remaped bad sectors/blocks be overwritten ?

Or is the 'only' way to acomplish the above is to use the secure erase method...
https://ata.wiki.kernel.org/index.php/ATA_Secure_Erase

Thank you.
Serene
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johnhudson
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Joined: Wed Aug 03, 2005 2:37 pm
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PostPosted: Tue Jan 01, 2013 10:43 pm    Post subject: Reply with quote

For a belt and braces approach try

http://www.sysresccd.org/SystemRescueCd_Homepage

which offers several options which do multiple overwrites to prevent recovery of any data. Read their documentation first if you want an explanation of why single overwrites may not deter a determined cracker.
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nelz
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Joined: Mon Apr 04, 2005 12:52 pm
Posts: 8467
Location: Warrington, UK

PostPosted: Tue Jan 01, 2013 11:06 pm    Post subject: Reply with quote

If you are that concerned about your data, or it really is that sensitive, play safe and destroy the drive.

Not only is a lump hammer more effective than dd, it is a damn sight more therapeutic too Smile
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Ram
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Joined: Thu Apr 07, 2005 10:44 pm
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Location: Guisborough

PostPosted: Wed Jan 02, 2013 1:46 am    Post subject: Reply with quote

nelz wrote:
If you are that concerned about your data, or it really is that sensitive, play safe and destroy the drive.

Not only is a lump hammer more effective than dd, it is a damn sight more therapeutic too Smile


Or drilling straight through the platters.
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ajgreeny
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Joined: Wed May 10, 2006 9:18 pm
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Location: Oxfordshire.

PostPosted: Wed Jan 02, 2013 11:31 am    Post subject: Reply with quote

There is a lot of apocryphal information that suggests that data can be retrieved from disks that have been overwritten several times, even after using such utilities as DBAN.

Having searched a few months ago, just out of interest, not because I had anything to wipe, it became quickly obvious that the cost of retrieval of anything from a disk that has been overwritten even once with zeros, but better with random data, was exorbitant, and only in the case of high forensic need would it ever be contemplated, and even then would probably fail.

This google search may put your mind at rest, but do your own fuller search if you want to.
http://www.google.co.uk/search?q=data+retrieval+ater+overwriting+disk+with+zeros&ie=UTF-8#hl=en&tbo=d&spell=1&q=data+retrieval+after+overwriting+disk+with+zeros&sa=X&ei=vBnkUMLkMKu00QWmmIGQDQ&ved=0CDIQvwUoAA&bav=on.2,or.r_gc.r_pw.r_qf.&bvm=bv.1355534169,d.d2k&fp=cf23a98e91636af7&bpcl=40096503&biw=1440&bih=718
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serene
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Joined: Sun Jun 19, 2005 1:43 pm
Posts: 111

PostPosted: Wed Jan 02, 2013 3:13 pm    Post subject: Reply with quote

A Happy New Year to all.

The question remains unanswered.
'Not' seeking alternative erase methods, recovery, physical destruction, risks.

I am seeking experience with using hard drive ATA Secure Erase command (Wipes all reserved areas including blocks reserved as bad) and is it "The Same" as using dd ?

For example;

dd bs=1M if=/dev/zero of=/dev/sda

vs.

hdparm --user-master u --security-erase NULL /dev/sda

Does anyone have 1st hand experience in determining if dd will wipe all reserved/hidden hard drive areas, including reserved bad blocks ?

Thank you.
Serene
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Paradigm Shifter



Joined: Sat May 19, 2012 1:16 pm
Posts: 84

PostPosted: Thu Jan 03, 2013 11:11 am    Post subject: Reply with quote

While I've only found a comment on a blog that mentions it so far, apparently Secure Erase does not touch bad sectors.

ref: (comment three)
http://ultraparanoid.wordpress.com/2007/09/12/securely-erase-hard-drives/

Happy new year. Wink
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serene
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Joined: Sun Jun 19, 2005 1:43 pm
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PostPosted: Thu Jan 03, 2013 3:49 pm    Post subject: Reply with quote

Paradigm Shifter,
Nice link.

The link you provided says;
"Summary:
ATA-SE methodology is superior to Block Erase methodology due to ATA-SEís ability to overwrite bad blocks, due to itís reduced time demand and due to itís improved completion feedback."

I have not found a reliable method to overwrite bad blocks.

Using dd interestingly results in the exact amount of wipe time as a secure ATA command.

By the way, if any of you are interested in using the ATA secure erase, the 'Parted Magic' live cd is great... use the "Disk Eraser".
I understand it to wipe all protected areas and reserved bad block areas by using the secure ATA commands, from a nice little GUI.
You can also use hdparm, but the GUI is pretty stress free.

You may want to see how long it will take for a secure erase, remain seated for a 3TB drive (ouch)....
$ hdparm -I /dev/sda | grep -i "enhanced security"
Results for 1TB;
$ 174min for SECURITY ERASE UNIT. 174min for ENHANCED SECURITY ERASE UNIT.

Thanks all... I'll continue research on my own. Some food for thought eh? It would be nice to know eventually if a simple dd will wipe all reserved/hidden areas of a hard drive.

Bye for now.

Cheers.
Serene
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