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. (On a related note, I did just such experiments in years past when an assertion as made that because Intel EPROMs were UV-erasable, that leaving them in the sun would erase them. We characterized the erasure in terms of UV photons per unit area, we calculated the erasure from first principles, and we did many rooftop measurements. Ditto for the claim that EPROMs and other chips could be affected by airport x-machines.) However, I plan to do some experiments over the next few days. I should have results by Saturday. [Friday night note: see results at end of this message.] Inasmuch as people leave music CDRs (and probably, now, CD-RWs) in their cars, where light leakage into CD jewel boxes is a fact of life, and inasmuch as there are not more (any?) reports of the music going away, I'm inclined to think a day in the sun is not enough to have the effect you are asserting. And there are "first principles" ways to check this claim: determining the dyes used, checking the sensitivity to solar radiation fluences, etc. The experiment is easy to do. Results of a quick experiment: a TDK data disk, one of the bluish ones, was left in the California sun for two (2) days. It had music on it. After two days in the sun, I washed it and dried it and put it in my player. No discernable loss of bits, as evidenced by no uncorrectable errors in the several minutes of music I listened to. While there may have been some bit errors, most of the bits were clearly still there. (Within the ability of the ECC system to correct.) Someone with access to BER (bit error rate) measurement programs or gear could do a more complete job (or someone could write actual data files and get some rough thresholds on number of errors). But the result is enough to satisfy me of this conclusion: "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. --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.
