3 ms·

Not an expert here (suggestions welcome), but maybe short of having some thermite at hand, multiple passes of dd if=/dev/urandom of=/dev/disk would be more effe

Not an expert here (suggestions welcome), but maybe short of having some thermite at hand, multiple passes of dd if=/dev/urandom of=/dev/disk would be more effective against well equipped parties. There are ways to extract data from zeroed platters in a clean room with the right equipment; writing random data multiple times should be harder to defeat.

hvidgaard 7y ago
I don't think anyone have ever demonstrated the ability to recover data after a few overwrites on any modern harddisk. The entire concept of "residual" magnetism that you can reliably measure sounds ridicules to an engineer.
- michaelt 7y ago
  AFAIK no-one has ever demonstrated the ability to recover data after a single overwrite. Someone offered a prize for such recovery, back in 2008 [1] which was never claimed (although the prize was only of symbolic value). [1] https://news.ycombinator.com/item?id=117588 https://news.ycombinator.com/item?id=117588
  - squarefoot 7y ago
    I don't want to sound like a conspiracy theorist, but if I was a 3 letter agency with infinite resources (so also no need to claim any prizes, no matter how much tempting they can be) and succeeded in recovering data that way, I would never tell anyone. Doing so would reveal what I can do, and by extension send the message "next time do a multiple pass wipe" which in the end would reveal what I cannot do.
    - hvidgaard 7y ago
      Considering that brilliant physicists and engineers have private access to state of the art technology, I find it highly unlikely that NSA/FBI/CIA/??? have figured out how to do this, but no one else have.
NKK6co7lnafKvg 7y ago
On Linux this will generally be CPU bound instead of IO bound because urandom is very slow. It's much faster to mount it as an encrypted drive with a random key and then dd over the encrypted mapping. Eg: cryptsetup open --type plain --key-file /dev/urandom --key-size 256 $DEV crypttmp dd if=/dev/zero of=/dev/mapper/crypttmp bs=4k

hvidgaard 7y ago

I don't think anyone have ever demonstrated the ability to recover data after a few overwrites on any modern harddisk. The entire concept of "residual" magnetism that you can reliably measure sounds ridicules to an engineer.

michaelt 7y ago
AFAIK no-one has ever demonstrated the ability to recover data after a single overwrite. Someone offered a prize for such recovery, back in 2008 [1] which was never claimed (although the prize was only of symbolic value). [1] https://news.ycombinator.com/item?id=117588 https://news.ycombinator.com/item?id=117588
- squarefoot 7y ago
  I don't want to sound like a conspiracy theorist, but if I was a 3 letter agency with infinite resources (so also no need to claim any prizes, no matter how much tempting they can be) and succeeded in recovering data that way, I would never tell anyone. Doing so would reveal what I can do, and by extension send the message "next time do a multiple pass wipe" which in the end would reveal what I cannot do.
  - hvidgaard 7y ago
    Considering that brilliant physicists and engineers have private access to state of the art technology, I find it highly unlikely that NSA/FBI/CIA/??? have figured out how to do this, but no one else have.

NKK6co7lnafKvg 7y ago

On Linux this will generally be CPU bound instead of IO bound because urandom is very slow. It's much faster to mount it as an encrypted drive with a random key and then dd over the encrypted mapping. Eg: cryptsetup open --type plain --key-file /dev/urandom --key-size 256 $DEV crypttmp dd if=/dev/zero of=/dev/mapper/crypttmp bs=4k