At 12:25 AM -0400 7/8/00, Dave Emery wrote: >On Fri, Jul 07, 2000 at 07:00:10PM -0700, Tim May wrote: >> At 12:45 AM +0200 7/6/00, Anonymous wrote: >> >CD-RW and green/blue CDRs are quite UV sensitive. The dye substrate is >> >eaten by UV, and the data is essentially just patches of more/less >> >reflective bits in that dye. Presumably, leaving one data-side-up in the >> >sun for a day or so should render it useless. >> >> >> The scientific method would be to do some experiments. >> >> "Leaving a CDR out in the sun for a couple of days is not a very good >> method for protecting data against snoopers." >> >> A long answer to a trival point, but it aroused my curiosity. Much as >> the claims that EPROMs could be erased with airport x-ray machines or >> inadvertent exposure to sunlight did, and much as claims that >> floppies are easily erased with small magnets. In none of these cases >> is the folk wisdom supported. > > > At the risk of continuing a somewhat off topic thread, it is my >understanding that the writing mechanism for CD-RWs is basicly thermal >and involves local heat induced changes in the crystaline structure of >the writeable layer induced by absorbed optical power from the pulsed >laser diode in the writer. Erasing CD-RWs before rewriting them is done >by annealing the written area with multiple passes of lower powered >heating from a continuous non pulsed laser diode. This all suggests to >me that perhaps a CD-RW could be erased by heating it in a oven or with >a heat lamp, perhaps only to temperatures that would not otherwise >render it useless by deforming the plastic substrate. Well, this gets back to the microwave stuff (by the way, we have this debate about destroying data with thermite, microwaves, etc. every six months or so, going back to 1992). Why, I have to ask, would you be interested in damaging the data without deforming or damaging the substrate or label or whatever? To fool the Fedz? Unlikely. For multiple reasons. > > And yes I am lazy and haven't yet tried this. > > I did try an experiment with heating video tapes up over the curie >point of the magnetic material once, however... This I _really_ find hard to believe. The Curie point of FeO and suchlike should be way, way above the melting point of the Mylar substrate. --Tim May -- ---------:---------:---------:---------:---------:---------:---------:---- Timothy C. May | Crypto Anarchy: encryption, digital money, ComSec 3DES: 831-728-0152 | anonymous networks, digital pseudonyms, zero W.A.S.T.E.: Corralitos, CA | knowledge, reputations, information markets, "Cyphernomicon" | black markets, collapse of governments.
