Dave Howe wrote:
Hmm. can you selectively blank areas of CD-RW?
Sure, you can. It isn't soooo much different from rewriting any other type of disk. There are various versions of getting rid of a disk file. 1) Deletion: Throwing away the pointer and putting the blocks back on the free list. This is well known to be grossly insecure. 2) Zeroizing the blocks in place (followed by deletion). This is vastly better, but still not entirely secure, because there are typically stray remnants of the pattern sitting "beside" the nominal track, and a sufficiently-determined adversary may be able to recover them. 3) Trashing the blocks, i.e. overwriting them in place with crypto-grade random numbers (followed by optional zeroizing, followed by deletion). This makes it harder for anyone to recover strays. 4) Half-track trashing. This requires wizardly disk hardware, which shifts the head half a track either side of nominal, and *then* writes random numbers. I might be persuaded that this really gets rid of strays. 5) Grinding the disk to dust. AFAIK this is the only NSA-approved method. A suitable grinder costs about $1400.00. http://cdrominc.com/product/1104.asp One drawback with this is that you have to destroy a whole disk at a time. That's a problem, because if you have a whole disk full of daily keys, you want to destroy each day's key as soon as you are through using it. There are ways around this, such as reading the disk into volatile RAM and then grinding the disk ... then you just have to make sure the RAM is neither more volatile nor less volatile than you wanted it to be. That is, you use the disk for *distribution* but not necessarily for intermediate-term storage. --------------------------------------------------------------------- The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]
