[Cryptography] Magnetic media destruction question

[Peter Gutmann]

John Levine <johnl at iecc.com> writes:

>T-7 is about shredding magnetic media, not paper.  I don't see what relevance
>that has.

Yup, it's pretty much completely irrelevant.  One is a collection of clearly-
labelled/identified bits of paper with the labelling visible to the naked eye,
the other is a mini-skip full of, let's say ten million because I'm too lazy
to sit down and do the volumetric calculation, identical fragments that have
all suffered severe mechanical trauma.  And it's not like when I looked at it
30+ years ago where you could use ferrofluid to get an idea of the geometry
and then try and recover the MFM data signal with an MFM (magnetic force
microscope) and a lot of effort, you're dealing with exotic recording
technologies where, and this is the bit I'm not sure about, you may need to
actually physically reconstruct the platter to be able to pull a signal off
it, or at least recover the encoding for the signal.  The bit density on a
fragment won't matter much if the only way to recover what's on there is to
have it moving under a read head at a given velocity with a flying height of a
few nanometers... on a shredded fragment with burrs and bends and other
damage.

Peter.