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> Since it has long been common practice to wipe disks by overwriting with random data Is it really that common of a practice to leave your entire disk full of

> Since it has long been common practice to wipe disks by overwriting with random data Is it really that common of a practice to leave your entire disk full of random data? I would expect that it's more common for disks to be full of zeros, or non-encrypted leftovers, than random data.

ciarannolan 6y ago
It's pretty uncommon for technically inclined folks to just abandon a disk with unencrypted data. And from what I remember reading long ago, several writes of random data is more secure than several (or one) writes of zeros.
- e12e 6y ago
  Depends on the disk (magnetic hard drive, density, type of storage (eg smr), flash/SSD etc). AFAIK for a recent (say, 2010 and later) drive - there's little to indicate random/"smart" patterns are better than just a single pass off all zeroes. Even if you consider an adversary with the capability to analyze drive with magnetic force microscopy. https://www.howtogeek.com/115573/htg-explains-why-you-only-have-to-wipe-a-disk-once-to-erase-it/ https://www.howtogeek.com/115573/htg-explains-why-you-only-h... https://www.sans.org/blog/overwriting-hard-drive-data/ https://www.sans.org/blog/overwriting-hard-drive-data/ "Data Reconstruction from a Hard Disk Drive using Magnetic Force Microscopy", 2013 Author(s): Kanekal, Vasu https://escholarship.org/uc/item/26g4p84b https://escholarship.org/uc/item/26g4p84b A quick skims seems to indicate the NSA recommends degaussuing and destruction: https://www.nsa.gov/resources/everyone/media-destruction/ https://www.nsa.gov/resources/everyone/media-destruction/ Nist 800-80: https://www.nist.gov/publications/guidelines-media-sanitization-0 https://www.nist.gov/publications/guidelines-media-sanitizat... Refers to: https://cmrr.ucsd.edu/resources/secure-erase.html https://cmrr.ucsd.edu/resources/secure-erase.html Who's readme: https://cmrr.ucsd.edu/_files/hdd-erase-readme.txt https://cmrr.ucsd.edu/_files/hdd-erase-readme.txt And q'n'a indicate that single pass sata secure erase is generally considered sufficient - it typically does a single pass, but should also write over all bad blocks etc. See also: https://ata.wiki.kernel.org/index.php/ATA_Secure_Erase https://ata.wiki.kernel.org/index.php/ATA_Secure_Erase
- phkamp 6y ago
  Wiping disks has not been possible and has not been trusted since embedded controllers on the disk-drives took over bad-block remapping in the late 1980-ies. It's even worse with SSD drives, where the "hidden reserve" many times larger. Wiping is of course better than doing nothing, but neither lives up to the requirements of GDPR. Where wiping disks is sufficient, for instance "internal reuse", it is always some number of specified writes, followed by writing all zeros, so both the donor and receiver can verify the disk as empty. Note that wiping a SSD with all-zeros is likely to be optimized out by its embedded controller.
- quickthrower2 6y ago
  That's my question, the non-abandonment of the disk is a clue that this scheme might have been used.

ciarannolan 6y ago

It's pretty uncommon for technically inclined folks to just abandon a disk with unencrypted data. And from what I remember reading long ago, several writes of random data is more secure than several (or one) writes of zeros.

e12e 6y ago
Depends on the disk (magnetic hard drive, density, type of storage (eg smr), flash/SSD etc). AFAIK for a recent (say, 2010 and later) drive - there's little to indicate random/"smart" patterns are better than just a single pass off all zeroes. Even if you consider an adversary with the capability to analyze drive with magnetic force microscopy. https://www.howtogeek.com/115573/htg-explains-why-you-only-have-to-wipe-a-disk-once-to-erase-it/ https://www.howtogeek.com/115573/htg-explains-why-you-only-h... https://www.sans.org/blog/overwriting-hard-drive-data/ https://www.sans.org/blog/overwriting-hard-drive-data/ "Data Reconstruction from a Hard Disk Drive using Magnetic Force Microscopy", 2013 Author(s): Kanekal, Vasu https://escholarship.org/uc/item/26g4p84b https://escholarship.org/uc/item/26g4p84b A quick skims seems to indicate the NSA recommends degaussuing and destruction: https://www.nsa.gov/resources/everyone/media-destruction/ https://www.nsa.gov/resources/everyone/media-destruction/ Nist 800-80: https://www.nist.gov/publications/guidelines-media-sanitization-0 https://www.nist.gov/publications/guidelines-media-sanitizat... Refers to: https://cmrr.ucsd.edu/resources/secure-erase.html https://cmrr.ucsd.edu/resources/secure-erase.html Who's readme: https://cmrr.ucsd.edu/_files/hdd-erase-readme.txt https://cmrr.ucsd.edu/_files/hdd-erase-readme.txt And q'n'a indicate that single pass sata secure erase is generally considered sufficient - it typically does a single pass, but should also write over all bad blocks etc. See also: https://ata.wiki.kernel.org/index.php/ATA_Secure_Erase https://ata.wiki.kernel.org/index.php/ATA_Secure_Erase
phkamp 6y ago
Wiping disks has not been possible and has not been trusted since embedded controllers on the disk-drives took over bad-block remapping in the late 1980-ies. It's even worse with SSD drives, where the "hidden reserve" many times larger. Wiping is of course better than doing nothing, but neither lives up to the requirements of GDPR. Where wiping disks is sufficient, for instance "internal reuse", it is always some number of specified writes, followed by writing all zeros, so both the donor and receiver can verify the disk as empty. Note that wiping a SSD with all-zeros is likely to be optimized out by its embedded controller.
quickthrower2 6y ago
That's my question, the non-abandonment of the disk is a clue that this scheme might have been used.