[Cryptography] Rubber-hose resistance?

[Arnold Reinhold]

On Wed, 20 Dec 2017 22:12: Jerry Leichter wrote:

...
> Maybe all zeroes are easier to remove.  Maybe a random bit pattern is easier to remove.  Take a simple analogy:  If you were talking about audio, a random bit pattern would be like high-frequency hiss, easily removed by a low-pass filter.
> …

Umm, no, you can't get rid of random noise with a filter. You can remove the annoying high frequency portion, but you remove the high frequency component of the signal as well. If you could reduce in-band noise with a passive filter, you could create a node with a lower noise temperature than the source and hence build a perpetual motion machine, violating the second law of thermodynamics. Writing zeros to a disk may be good enough to prevent data recovery, but writing random data is no worse. 

Of course this is mostly moot with the rise of SSDs, which, as others have pointed out, are hard to erase with any certainty. Recent Apple’s iOS devices solve this by encrypting the entire volume with a key stored in a special “effaceable memory” that they erase when you reset the device. SSH clients are available for iOS, so one can travel with a clean device and download sensitive data after crossing a border and then reset the device before leaving. A reset takes only a few minutes. The device reboots to factory settings once you get through several “are you sure you really want to do this?” screens. The procedure simple enough for someone without computing skills to do.

Arnold Reinhold