On Sun, Jul 22, 2007 at 01:52:35PM -0700, Robert Howard wrote: > How about deleting confidential data from hard disks! > > The solution today is to overwrite it many times with random data. > > But modern mathematics and technology makes it possible to recover the much > of the original text given the original random sequence used to delete the > data. Given a long sequence of deleted white space (or zeros on the disk), > then it becomes possible to recover the original pseudo-random sequence (for > example, one based on linear > <http://en.wikipedia.org/wiki/Linear_congruence_theorem> congruence) - even > if a many passes are performed. > > With a true random number generator, only one pass is needed. > > I'm sure hardware random number generators based on quantum effects, which > have been around for decades, would be used instead of hitting a web site, > which compromises the who shebang. > > > > Robert Howard > > Phoenix, Arizona > >
You don't even need to do that. Entropic sources are available from considering timings on a system undergoing interrupts from external sources (eg mouse or keyboard activity). The Linux kernel performs this analysis and provides a conveniently encapsulated device called /dev/random. I used used precisely this technique to implement a disk erasing program a couple of years ago - and offered the possibility to do it multiple times for the absolutely paranoid. Note that /dev/random has rather unpredictable performance - you are advised to shake you mouse, or something like that when generating a seed for ssh for instance. To improve its performance, you use the output of /dev/random to fill a table, which is continually overwritten as new random bits become available, Then you use a conventional pseudo RNG to index into the table, so the resulting bitstream has small chunks of "correlated" numbers, but is by and large unpredictable. The state of the art for doing this is a library called Havege. Look it up if you're interested. Cheers -- ---------------------------------------------------------------------------- A/Prof Russell Standish Phone 0425 253119 (mobile) Mathematics UNSW SYDNEY 2052 [EMAIL PROTECTED] Australia http://www.hpcoders.com.au ---------------------------------------------------------------------------- ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org
