I got the basics. Deleting a file simply tells the system that the sectors it occupied are now available for new data to be written on.
But if you want a more secure deleting why cannot you just overwrite everything with zeroes? If the computer system is only working at its core by manipulating zeroes and ones, why is it said that physically destroying the drive the information is stored on, is the only secure way to make sure nothing is left on it?
In: Technology
Back in the last century I built mil-spec disk storage systems. Some were used to store highly classified data, for fun customers like NSA and SAC. So I learned a lot about secure data destruction.
First, overwriting stored data with 0s is mostly adequate, unless your Bad Guy has serious technical resources. That’s because, while your computer would read it as 0, some residual traces of the earlier magnetization are still there. That’s because the “track” where the magnetic data is recorded is a bit wobbly, so the overwrite might not completely overwrite every bit. Like a bad repaving job on a country road. Reading that leftover info varies from easy to extremely difficult, depending largely on how dense the data is on the disk platter itself.
Another issue is that modern OS and storage systems often virtualize the disk in some way. This means that if you have a file that looks to The OS like it is in sector 3, it could actually be anywhere at the hardware level. Asking the OS to overwrite sector 3 might have no effect at the low level hardware. Secure erase requires low level hardware support.
Back when 240 MB on 4 8-inch wide platters was the norm, it was relatively easy to see the old data. At today’s densities it might be impossible. But, while interesting, it’s mostly irrelevant because…
All my customers who cared about data-erase specified multiple overwrites, with various bit patterns. Sometimes many many overwrites, in an effort to remove any trace Of The secret data. I wrote a data erase routine for a 3-letter agency that took 45 minutes to complete, on a disk less than 1 GB. But even that didn’t really matter, because…
They installed a thermite incendiary destruction device in the rack, which took a whole 30 seconds to work. For a different customer, I asked how erase should be done in case the disk needed warranty repair work. They said, “Don’t worry. If it breaks, we crush and shred it, then burn the scrap. Just sell us a new one. ”
Your tax dollars at work, folks.
Latest Answers