Let's assume that I have a modern magnetic (not SSD) hard drive, manufactured within the past ten years, and the hard drive is packed with the only copies of an unpublished paper about cheap cold fusion written by a scientist who died in the fire that burned down the only cold fusion lab in the world.
dd if=/dev/zero of=/dev/sdx
I've heard people say that if you want to be sure that the data is completely erased, you need to:
Use random data, not zeroes.
Zero the hard drive with multiple passes, either 7 ("standard" practice) or 35 (for the truly paranoid).
Erase using passes that have special alternating patters. Supposedly, this either degausses the original signal or adds enough extra noise that you can't pick it out.
Perform some kind of "low level" erase that causes the heads to move in different patterns, or causes the bit patterns to differ. This requires hardware support.
Raise the platters above their Curie temperature
My question is: is it actually possible to recover data from a zeroed drive? In other words, is it justifiable to use random data / multiple passes / etc. to bury your digital secrets?
I understand that "The Great Zero Challenge" (40 USD prize) has not been won, but hypothetically, if cost of such recovery is large or secret enough, then it's a moot point.